## 1. Intellectual Biography


### 1.1 Early life and education



Descartes was born on 31 March 1596 in his maternal
grandmother's house in La Haye, in the Touraine region of
France. His father Joachim, a lawyer who lived in Chatellerault
(22 kilometers southwest of La Haye, across the Creuse River in the
Poitou region), was away at the Parliament of Brittany in Rennes. The
town of La Haye, which lies 47 kilometers south of Tours, has
subsequently been renamed Descartes.



When Descartes was thirteen and one-half months old, his mother,
Jeanne Brochard, died in childbirth. The young Rene spent his
early years with his grandmother, Jeanne Sain Brochard, in La Haye,
together with his older brother Pierre and older sister Jeanne. It is
likely that he then moved to the house of his great uncle, Michel
Ferrand, who, like many of Rene's male relatives, was a
lawyer; he was a Counselor to the King and held the royal office of
provincial Lieutenant General in Chatellerault. When Descartes
met Isaac Beeckman in 1618, he introduced himself as
"Poitevin," or from Poitou (*10:46, 51-4*;
Rodis-Lewis 1998, 3, 26; see also *2:642*). At this time (and
now and again later on), he also signed letters as "du
Perron" and called himself "sieur du Perron" (Lord
of Perron), after a small farm in Poitou he inherited from his
mother's family (Watson 2007, 81, 230). But he did not neglect
his birthplace in La Haye: in a letter of 1649, he described himself
as "a man who was born in the gardens of Touraine"
(5:349).



In 1606 or 1607, Descartes, a Roman Catholic, entered the newly
founded Jesuit College of La Fleche, where he remained until
1614 or 1615. He followed the usual course of studies, which included
five or six years of grammar school, including Latin and Greek
grammar, classical poets, and Cicero, followed by three years of
philosophy curriculum. By rule, the Jesuit philosophy curriculum
followed Aristotle; it was divided into the then-standard topics of
logic, morals, physics, and metaphysics. The Jesuits also included
mathematics in the final three years of study.



Aristotle's philosophy was taught through textbooks and printed
commentaries on his works. Aristotle himself frequently discussed the
positions of his ancient predecessors. The most extensive commentaries
also elaborated in some detail on positions other than
Aristotle's. Within this framework, and taking into account the
reading of Cicero, Descartes would have been exposed in school to the
doctrines of the ancient atomists, Plato, and the Stoics, and he would
have heard of the skeptics. Further, important intellectual events
were celebrated at La Fleche, including Galileo's
discovery of the moons of Jupiter in 1610. Although scholastic
Aristotelian philosophy was dominant in Descartes' school years,
it was not the only philosophy that he knew.



Famously, Descartes wrote in the autobiographical portion of the
*Discourse* (1637) that, when he left school, "I found
myself beset by so many doubts and errors that I came to think I had
gained nothing from my attempts to become educated but increasing
recognition of my ignorance" (6:4). And yet, he continued, he
did not "cease to value the exercises done in the schools"
(6:5), for languages, fables, oratory, poetry, mathematics, morals,
theology, and philosophy all had their value, as did jurisprudence,
medicine, and other sciences (including engineering) that serve as
professions and which one might study after attending a school such as
La Fleche. He noted the contradiction and disagreement that
beset philosophy and so infected the higher sciences (including
medicine) "insofar as they borrow their principles from
philosophy" (6:8). A year later, in 1638, he told an inquiring
father that "nowhere on earth is philosophy taught better than
at La Fleche," where he advised his correspondent to send
his son even if he wanted him subsequently to transcend the learning
of the schools--while also suggesting that the son might study at
Utrecht with Henry le Roy, a disciple of Descartes (2:378-9).
According to the *Discourse*, it was not surprising that
philosophy as taught at La Fleche was uncertain: it had to be,
since he (Descartes) was now offering a first glimpse of the one true
philosophy, only recently discovered. Until it could be promulgated,
La Fleche, or another good school, would do.



His family wanted Descartes to be a lawyer, like his father and other
relatives. To this end, he obtained a law degree from Poitiers in
1616. But he never practiced law or entered into the governmental
service that such practice would have made possible (Rodis-Lewis 1998,
18-22). Instead, he became a gentleman soldier, moving in 1618
to Breda, to support the Protestant Prince Maurice against the
Catholic parts of the Netherlands (which later constituted Belgium),
which were controlled by Spain--a Catholic land, like France, but
at this point an enemy.


### 1.2 First results, a new mission, and method



While in Breda, Descartes met Isaac Beeckman, a Dutch mathematician
and natural philosopher. Beeckman set various problems for Descartes,
including questions about falling bodies, hydrostatics, and
mathematics. Descartes and Beeckman engaged in what they called
"physico-mathematica," or mathematical physics
(Beeckman's journal, in Descartes, *10:52*). Since
antiquity, mathematics had been applied to various physical subject
matters, in optics, astronomy, mechanics (focusing on the lever), and
hydrostatics. Beeckman and Descartes brought to this work a commitment
to atoms as the basic constituents of matter. As had ancient atomists,
they attributed not only size, shape, and motion but also weight to
those atoms (*10:68*). Descartes opened a section in his
notebook entitled "Democritica" *(10:8)*, in honor
of the ancient atomist Democritus.



Perhaps at this time, though certainly by 1628, Descartes had the
fundamental insight that makes analytic geometry possible: the
technique for describing lines of various sorts by using mathematical
equations involving ratios between lengths in relation to coordinate
lines. (Descartes did not require that the lines be perpendicular to
one another.) Descartes himself did not foresee replacing geometrical
constructions with algebraic formulas; rather, he viewed geometry as
the basic mathematical science and he considered his algebraic
techniques to provide an extension beyond compass-and-ruler
constructions. When the right-angled coordinate system of algebraic
geometry was subsequently developed, the name "Cartesian
coordinates" honored Descartes' discovery. (See Boyer
1968, Ch. 17, Shea 1991, Ch. 3, and, more generally, Domski 2022.)



Descartes left Breda in 1619 to join the Catholic army of Maximilian I
(Duke of Bavaria and ally of France). The war concerned the authority
of Ferdinand II, a Catholic, who in September had been crowned emperor
of the Holy Roman Empire (located in Central Europe and including
Austria and parts of northern Italy). Descartes attended the
coronation and was returning to the army when winter caught him in the
small town of Ulm (or perhaps Neuburg), not far from Munich. On the
night of 10 November 1619, he had three dreams that seemed to provide
him with a mission in life. The dreams themselves are interesting and
complex (see Sebba 1987). Descartes took from them the message that he
should set out to reform all knowledge. He decided to begin with
philosophy, since the principles of the other sciences must be derived
from it (*Disc*. II, 6:21-2).



Descartes was familiar with both mainstream philosophy and recent
innovators (those who, among other things, rejected aspects of
Aristotle's philosophy), from both his schooling and from
reading he undertook from 1620 on. In 1640, he recalled
(*Corr*. 3:185) having read various works in philosophy around
the year 1620, written by well-known Jesuit commentators on Aristotle:
Francisco Toledo (1532-96), Antonio Rubio (1548-1615), and
the Coimbran commentators (active ca. 1600). He also recalled an
abstract or summary of "the whole of scholastic
philosophy" by Eustace of Saint Paul (1573-1640), whose
*Summa Philosophiae* was first published in 1609. In 1638, he
recalled having read Thomas Campanella's *De Sensu Rerum*
(1620) about fifteen years before, and not being much impressed
(2:659-60). And in 1630 he was able to rattle off the names of
recent innovators in philosophy (1:158), including Campanella
(1568-1639), Bernardino Telesio (1509-88), Giordano Bruno
(1548-1600), Lucilio Vanini (1585-1619), and
Sebastien Basson (b. ca. 1573). From these sources, he would
have acquired basic philosophical concepts, such as the notion that
substances are characterized by essences that determine which
properties they must have in order to be what they are (an
Aristotelian concept). He would also have seen first attempts, among
the innovators, of reviving atomism, or of challenging the notion of
substantial forms (see Sec. 1.3).



Descartes' activities during the early 1620s are not
well-documented. He was in France part of the time, visiting Poitou to
sell some inherited properties in 1622 and visiting Paris. He also
went to Italy (1623-25). Upon his return he lived in Paris,
where he was in touch with mathematicians and natural philosophers in
the circle of his long-time friend and correspondent Marin Mersenne
(1588-1648). While in Paris, he worked on some mathematical
problems and derived the sine law of refraction, which facilitated his
work on formulating mathematically the shapes of lenses (later
published in the *Dioptrics*). His major philosophical effort
during these years was on the *Rules*.



In the *Rules*, he sought to generalize the methods of
mathematics so as to provide a route to clear knowledge of everything
that human beings can know. His methodological advice included a
suggestion that is familiar to students of elementary geometry: break
your work up into small steps that you can understand completely and
about which you have utter certainty, and check your work often. But
he also had advice for the ambitious seeker of truth, concerning where
to start and how to work up to greater things. Thus, Rule 10 reads:
"In order to acquire discernment we should exercise our
intelligence by investigating what others have already discovered, and
methodically survey even the most insignificant products of human
skill, especially those which display order" (10:403). As
examples of "simple" arts "in which order
prevails" (10:404), he offered carpet-making and embroidery, and
also number-games and arithmetic games. He went on to discuss the
roles of the "cognitive faculties" in acquiring knowledge,
which include the intellect, imagination, sense perception, and
memory. These faculties allow the seeker of knowledge to combine
simple truths in order to solve complex problems as found in optics
(10:394) or to discover how a magnet works (10:427).



By the end of 1628, Descartes abandoned work on the *Rules*,
having completed about half of the projected treatise. He moved to the
Dutch Netherlands, returning to France only infrequently prior to
moving to Sweden in 1649. While in the Netherlands, he tried to keep
his address secret and changed locations often, according to his
motto, "who lives well hidden, lives well" (1:286\*).


### 1.3 Metaphysical turn, comprehensive physics, *Discourse*



Descartes spent his first year in the Netherlands in Franeker, where
he registered at the University in April, 1629. Initially, he worked
on two topics: mathematical science and metaphysics. In Summer, 1629,
an impressive set of parhelia, or false suns, were observed near Rome.
When Descartes heard of them, he set out to find an explanation. (He
ultimately hypothesized that a large, solid ice-ring in the sky acts
as a lens to form multiple images of the sun [*Met*.
6:355].)



This work interrupted his investigations on another topic, which had
engaged him for his first nine months in the Netherlands
(1:44)--the topic of metaphysics. The metaphysical objects of his
investigation included the existence and nature of God and the soul
(1:144, 182). However, these metaphysical investigations were not
entirely divorced from problems such as the parhelia, for he claimed
that through his investigations into God and the human self, he had
been able "to discover the foundation of physics" (1:144).
His post-*Rules* emphasis on intellectual apprehension of God,
the soul, and the foundations of physics constitute Descartes'
"metaphysical turn," even if his metaphysics was not yet
fully disclosed. Subsequently, Descartes mentioned a little
metaphysical treatise in Latin--presumably an early version of
the *Meditations*--that he wrote upon first coming to the
Netherlands (1:184, 350). And he later affirmed to Mersenne that the
metaphysics of the *Meditations*, in which God and soul are
prominent, contained "all the principles of my physics"
(3:233).



While working on the parhelia, Descartes conceived the idea for a very
ambitious treatise, about which he wrote Mersenne on 16 November 1629
from his new residence in Amsterdam. He now intended to explain not
"just one phenomenon" (the parhelia), but "all the
phenomena of nature, that is to say, the whole of physics"
(1:70). This work eventually became *The World*, which was to
have three parts: on light (a general treatise on visible, or
material, nature), on man (a treatise on physiology), and on the soul.
Only the first two survive (and perhaps only they were ever written),
as the *Treatise on Light* and *Treatise on Man*. In
these works, which Descartes decided to suppress upon learning of the
condemnation of Galileo (1:270, 305), he offered a comprehensive
vision of the universe as constituted from bare matter possessing the
properties length, breadth, and depth (three-dimensional volume) and
carved up into particles with size and shape, which may be in motion
or at rest, and which interact through quantitative laws of motion
that are formulated and sustained by God (*Light*,
11:33-4). These works described the visible universe as a single
physical system in which all operations, from the formation of planets
and the transmission of light from the sun to the physiological
processes of human and nonhuman animal bodies, can be explained
through the mechanism of matter arranged into shapes and structures
and moving according to three laws of motion. In fact, his
explanations in the *World* and the subsequent
*Principles* made little use of the three laws of motion in
other than a qualitative manner. The laws sustained the notion that
matter moves regularly (in a straight line) and that upon impact bits
of matter alter their motions in regular ways--something that
happens constantly in the full universe (the "plenum")
conceived by Descartes. (At this time, Descartes received an offer of
appointment to the medical faculty in Bologna--even though he had
not yet made public any of his results--which he declined; see
Manning 2014.)



After suppressing his *World*, Descartes decided to put
forward, anonymously, a limited sample of his new philosophy, in the
*Discourse* with its attached essays. The *Discourse*
recounted Descartes' own life journey, explaining how he had
come to the position of doubting his previous knowledge and seeking to
begin afresh. It offered some initial results of his metaphysical
investigations, including mind-body dualism. It did not,
however, engage in the deep skepticism of the later
*Meditations*, nor did it claim to establish, metaphysically,
that the essence of matter is extension. This last conclusion was
presented merely as a hypothesis whose fruitfulness could be tested
and "proven," or perhaps merely confirmed (see McMullin
2008), by the results contained in the attached essays on
*Dioptrics* and *Meteorology* (the latter covering
"atmospheric" phenomena).



In his *Meteorology*, Descartes described his general
hypothesis (or supposition) about the nature of matter, before
offering accounts of vapors, salt, winds, clouds, snow, rain, hail,
lightning, the rainbow, coronas, and parhelia. His hypothesis was as
follows:



> 
> 
> that the water, earth, air, and all other such bodies that surround us
> are composed of many small parts of various shapes and sizes, which
> are never so properly disposed nor so exactly joined together that
> there do not remain many intervals around them; and that these
> intervals are not empty but are filled with that extremely subtle
> matter through the mediation of which, I have said above, the action
> of light is communicated. (6:233)
> 
> 
> 



He presented a corpuscularian basis for his physics that denied the
atoms-and-void theory of ancient atomism and affirmed that all bodies
are composed from one type of matter, which is infinitely divisible
into particles or corpuscles (6:239). He here also proclaimed that his
natural philosophy had no need for the "substantial forms"
and "real qualities" that other philosophers (i.e.,
Aristotelians) "imagine to be in bodies" (6:239). He had
taken the same position in the *Treatise on Light*, where he
said that in conceiving his new "world" (i.e., his
conception of the universe), "I do not use the qualities called
heat, cold, moistness, and dryness, as the Philosophers do"
(11:25).



In effect, he was denying the then-dominant scholastic Aristotelian
ontology, which explained all natural bodies as comprised of a
"prime matter" informed by a "substantial
form," and which explained qualities such as hot and cold as
really inhering in bodies in a way that is "similar" to
the qualities of hot and cold as we experience them tactually.
According to the Aristotelian explanation, the qualities that are
proper to each sense--color, sound, odor, tastes, and tactual
qualities--are really inherent in things, and our experienced
sensations resemble these qualities in things. As regards prime
matter, many scholastic Aristotelians held that it cannot exist on its
own; to form a substance, or something that can exist by itself, prime
matter must be "informed" by a substantial form (a form or
active principle that gives a substance its essential properties). The
four Aristotelian elements, earth, air, fire, and water, had
substantial forms that combined the basic qualities of hot, cold, wet,
and dry: earth is cold and dry; air is hot and wet; fire is hot and
dry; and water is cold and wet. These elements can themselves then
serve as "matter" to higher substantial forms, such as the
form of a mineral, or a magnet, or a living thing. Whether in the case
of earth or of a living thing, such as a rabbit, the
"form" of a thing directs its characteristic activity. For
earth, that activity is to approach the center of the universe; water
has the same tendency, but not as strongly. Accordingly, Aristotelians
explained, the planet earth exists at the center, with water on its
surface. A new rabbit is formed when a male rabbit contributes,
through its seed-matter, the "form" of rabbithood to the
seed-matter of the female rabbit. This form then organizes that matter
into the shape of a rabbit, including its various organs and
physiological processes. The newborn rabbit's behavior is guided
by its "sensitive soul," a rabbit-specific instance of the
type of substantial form possessed by all animals. Other properties of
the rabbit, such as the whiteness of its fur, are explained by the
"real quality" of white inhering in each strand of
hair.



Although in the *World* and *Meteorology* Descartes
avoided outright denial of substantial forms and real qualities, it is
clear that he intended to deny them (*Corr*. 1:324; 2:200;
3:420, 500, 648). Indeed, he claimed that he could explain these
qualities themselves through matter in motion (*Light* 11:26,
*Met*. 6:235-6). As an example, he explained color in
things as a property of surfaces that puts a spin on particles of
light, which in turn affect the nerves in the retina, which then
affect the brain, causing a sensation in the mind (via matter's
effect on the immaterial mind). The sensation of a color (such as red)
does not resemble the surface property that causes the effect on the
nerve that produces the sensation. The experienced red is an
apparently arbitrary sign or signal for a surface property in objects
(*Light* I; see also *Dioptrics* VI, 6:130, and
*Princ*. I.68-70).



Two considerations help explain Descartes' tentative language
with respect to substantial forms and real qualities. First, when he
wrote these works in the 1630s, he was not yet prepared to release his
metaphysics, which would support his hypothesis about matter and so
rule out substantial forms (1:563). Second, he was sensitive to the
prudential value of not directly attacking the scholastic Aristotelian
position (3:298), since it was the accepted position in university
education (3:577) and was strongly supported by orthodox theologians,
both Catholic and Protestant (1:85-6; 3:349).



After the *Discourse* appeared in 1637, Descartes received
letters with queries and challenges to various of the doctrines,
including: his avoidance of substantial forms and real qualities; his
argument for a distinction between mind and body; and his view that
natural philosophical hypotheses could be "proven" (or
confirmed) through the empirically observed effects they explain
(*Disc*. VI, 6:76). This correspondence merits close study, for
his further discussions of hypothesis-confirmation in science
(*Corr*. 1:422-4, 563-4, 2:142-3,
199-201), his replies to objections concerning his metaphysics
(1:350, 353), and his explanation that he had left the most radical
skeptical arguments out of this work, since it was written in French
for a wide audience, including women (1:350, 561).



In 1635, Descartes fathered a daughter named Francine. Her mother was
Descartes' housekeeper, Helena Jans. They lived with Descartes
part of the time in the latter 1630s. He was arranging for the
daughter to live with a female relative of his for the sake of her
education when he learned of her death in September 1640, which
saddened him greatly (Rodis-Lewis 1998, 140). Subsequently, in 1644,
he contributed a dowry for Helena's marriage (Watson 2007,
188).


### 1.4 The metaphysics and comprehensive physics revealed



In a letter of 13 November 1639, Descartes wrote to Mersenne that he
was "working on a discourse in which I try to clarify what I
have hitherto written" on metaphysics (2:622). This was the
*Meditations*, and presumably he was revising or recasting the
Latin treatise from 1629 and elaborating on *Discourse* IV. He
told Mersenne of his plan to provide the work to "the twenty or
thirty most learned theologians" so as to gauge their responses
before publication. Ultimately, he and Mersenne collected seven sets
of objections to the *Meditations*, which Descartes published
with the work, along with his replies (1641, 1642). Some objections
were from unnamed theologians, passed on by Mersenne; one set came
from the Dutch priest Johannes Caterus; one set was from the Jesuit
philosopher Pierre Bourdin; others were from Mersenne himself, from
the philosophers Pierre Gassendi and Thomas Hobbes, and from the
Catholic philosopher-theologian Antoine Arnauld.



Recall that Descartes considered the *Meditations* to contain
the principles of his physics. But there is no Meditation labeled
"principles of physics." The principles in question, which
are spread through the work, concern the nature of matter, the
activity of God in creating and conserving the world, the nature of
mind (that it is an unextended, thinking substance), mind-body
union and interaction, and the ontology of sensory qualities.



Once Descartes had presented his metaphysics, he felt free to move
beyond the published samples of his physics and to present the whole
of his conception of nature. But he needed first "to teach it to
speak Latin" (3:523), the lingua franca of the seventeenth
century (recall that his *World* was in French). He hatched a
scheme to publish a Latin version of his physics (the
*Principles*) accompanied by a scholastic Aristotelian work on
physics, so as to make the comparative advantages manifest. He chose
the *Summa philosophiae* of Eustace of St. Paul. That part of
his plan never came to fruition. His intent remained the same: he
wished to produce a book that could be adopted in the schools, even
Jesuit schools such as La Fleche (3:233, 523; 4:224).
Ultimately, his physics was taught in the Netherlands, France,
England, and parts of Germany. For the Catholic lands, the teaching of
his philosophy was dampened when his works were placed on the Index of
Prohibited Books in 1663, although his followers in France, such as
Jacques Rohault (1618-72) and Pierre Regis (1632-1707),
continued to promote Descartes' natural philosophy.



The *Principles* appeared in Latin in 1644, with a French
translation in 1647. Descartes added to the translation an
"Author's Letter" as a preface. The letter explained
important aspects of his attitude toward philosophy, including the
view that, in matters philosophical, one must reason through the
arguments and evaluate them for one's self (9B:3). He also
presented an image of the relations among the various parts of
philosophy, in the form of a tree:



> 
> Thus the whole of philosophy is like a tree. The roots are
> metaphysics, the trunk is physics, and the branches emerging from the
> trunk are all the other sciences, which may be reduced to three
> principal ones, namely medicine, mechanics and morals. By
> "morals" I understand the highest and most perfect moral
> system, which presupposes a complete knowledge of the other sciences
> and is the ultimate level of wisdom. (9B:14)
> 



The extant *Principles* offers metaphysics in Part I; the
general principles of physics, in the form of his matter theory and
laws of motion, as following from the metaphysics, in Part II; Part
III concerns astronomical phenomena; and Part IV covers the formation
of the earth and seeks to explain the properties of minerals, metals,
magnets, fire, and the like, to which are appended discussions of how
the senses operate and a final discussion of methodological issues in
natural philosophy. His intent had been also to explain in depth the
origins of plants and animals, human physiology, mind-body union
and interaction, and the function of the senses. (Descartes and his
followers variously included topics concerning the nature of the mind
and mind-body interaction within physics or natural philosophy,
on which, see Hatfield 2000.) In the end, he had to abandon the
discussion of plants and animals (*Princ*. IV.188), but he
included some discussion of mind-body union in his abbreviated
account of the senses.


### 1.5 Theological controversy, *Passions*, and death



From early in his correspondence with Mersenne, Descartes expressed
concern to avoid becoming embroiled in theological controversy or
earning the enmity of church authorities (1:85-6, 150, 271).
Aside from such prudential concerns, he strictly separated theological
doctrines based in faith (e.g., the trinity) from his claims about God
based solely in reason (*Corr*. 1:44, 150, 153; 4:117).
Descartes was a Roman Catholic, but it is clear that the God of his
metaphysics is nondenominational, tending toward the deistic. If
Descartes were fully consistent, he would make no claims about
God's plans or his Providential acts and there would be no
miracles in his world (*Light* VII, 11:48; *Princ*.
III.2-3; see also *Corr*. *2:558*, 3:214).



Despite his precautions, he was drawn into theological controversy
with the Jesuits over Bourdin's set of objections, which led him
to write to Father Dinet, Bourdin's superior, to allay any fears
that Descartes' philosophy caused theological difficulty
(7:581). He was also drawn into theological controversy with Calvinist
theologians in the Netherlands. In the latter 1630s, Henry le Roy
(1598-1679), or Regius, a professor of medicine in Utrecht,
taught Descartes' system of natural philosophy. Already by 1640,
Gisbertus Voetius (1589-1676), a theologian at Utrecht,
expressed his displeasure over this to Mersenne (3:230). Controversy
brewed, and Descartes included an attack on Voetius in the Letter to
Dinet. Voetius, as rector of the University, convinced the faculty
senate to condemn Descartes' (and Regius') philosophy in
1642. He and his colleagues attacked Descartes in disputations in 1642
and in a book by Martin Schoock (1643), to which Descartes responded
with a *Letter to Voetius* (1643). The controversy simmered.
Descartes eventually fell out with Regius, who published a broadsheet
manifesto that deviated from Descartes' theory of the human
mind. Descartes replied with his *Comments on a Certain
Broadsheet* (1648). In 1648 he drafted a further response to
ongoing attacks by Voetius, ultimately published in 1656 (*Querela
apologetica*).



In the mid-1640s, Descartes continued work on his physiological
system, which he had pursued throughout the 1630s. He allowed the
unpublished manuscript of the *Treatise on Man* to be copied
(4:566-7) and he began a new work (5:112), *Description of
the Human Body*, in which he sought to explain the embryonic
development of animal bodies. During this period he corresponded with
Princess Elisabeth of Bohemia (daughter of Frederick V, a Protestant,
and briefly King of Bohemia), now living in the Netherlands, at first
on metaphysical topics from the *Meditations* and then on the
passions and emotions. Eventually, he wrote the *Passions of the
Soul* (1649), a comprehensive and original theory of the passions
and emotions that presented the most extensive account of his
behavioral physiology published during his lifetime.



In 1649, Descartes accepted the invitation of Queen Christina of
Sweden to join her court. At her request, he composed the Statutes of
the Swedish Royal Academy. On the day he gave them to her, he became
ill. He never recovered, and died on 11 February 1650. (On
Descartes' intellectual biography, see Clarke 2006, Gaukroger
1995, and Rodis-Lewis 1998.)


## 2. Philosophical Development



In general, it is rare for a philosopher's positions and
arguments to remain the same across an entire life. This means that,
in reading philosophers' works and reconstructing their
arguments, one must pay attention to the place of each work in the
philosophical development of the author. Readers of Immanuel Kant are
aware of the basic distinction between his critical and precritical
periods. Readers of G. W. Leibniz are also aware of his philosophical
development, although in his case there is less agreement on a
developmental scheme.



Scholars have proposed various schemes for dividing Descartes'
life into periods. This entry adopts a relatively simple division
between the era when mathematics provided the model for his method (in
the *Rules*) and the period after the "metaphysical
turn" of 1629, when his conception of the role of the intellect
in acquiring knowledge changed to privilege purely intellectual
intuitions. At this time, he also recognized that the truth of his
special or particular hypotheses in natural philosophy was less than
certain and so was subject to confirmation through consequences (as
mentioned in Sec. 1.3, above). In effect, he adopted what is now
called a hypothetico-deductive scheme of confirmation, but with this
difference: the range of hypotheses was limited by his metaphysical
conclusions concerning the essences of mind and matter, their union,
and the role of God in creating and conserving the universe.
Consequently, some hypotheses, such as the "substantial
forms" of the scholastics, were ruled out. Argumentative
differences among the *World*, *Discourse*, and
*Meditations* and *Principles* may then be ascribed to
the fact that, in the 1630s, Descartes had not yet presented his full
metaphysics and so adopted an empirical mode of justification for even
the first principles of his physics, whereas, after 1641, he appealed
to his published metaphysics in securing those principles.



Other scholars see things differently. John Schuster (1980) finds that
the epistemology of the *Rules* lasted into the 1630s and was
superseded (unhappily, in his view) only by the metaphysical quest for
certainty of the *Meditations*. Daniel Garber (1992, 48) also
holds that Descartes abandoned his early method only after the
*Discourse*. In contrast, Peter Machamer and J. E. McGuire
(2006) believe that Descartes held natural philosophy to the standard
of absolute certainty through the *Meditations* but admitted
defeat on that score at the end of *Principles* IV, adopting a
lower standard of certainty for his particular hypotheses (such as the
explanation of magnetism by corkscrew-shaped particles). They see the
*Principles* as marking Descartes' "epistemic
turn" away from the methodological stance of realism about
intuitive knowledge of substances that they find in the
*Rules*, *Discourse*, and *Meditations*.



Some scholars who emphasize epistemology find that the main change in
Descartes' intellectual development is the introduction of
skeptical arguments in the *Discourse* and
*Meditations*. Some interpreters, perhaps inspired by Richard
Popkin (1979), believe that Descartes took the skeptical threat to
knowledge quite seriously and sought to overcome it in the
*Meditations* (e.g., Curley 1978). By contrast, in the
interpretive thread followed here, skeptical arguments were a
cognitive tool used to guide the reader of the *Meditations*
into the correct cognitive frame of mind for grasping the first truths
of metaphysics. An answer to skepticism was a side-effect of this
fundamental aim.



Other views of Descartes' development have arisen from new
attention to the biological and physiological dimensions of his
thought. A key element is Descartes' fascination with mechanical
automata and his use of the notion of a machine in characterizing
living things (*Man* 11:119-20, 130-31;
*Med*. VI, 7:84). Here again the fundamental change occurs just
after the *Rules*; it is not a "metaphysical turn"
but a turn toward automata as models for human and animal behavior.
These interpretations connect with Descartes' new theory of
perception (Ben-Yami 2015) or his investigation of ordinary objects
and living things as coherent unities (Brown and Normore 2019; see
also Des Chene 2001).


## 3. A New Metaphysics and Epistemology



Descartes presented his metaphysics first in the *Meditations*
and then, in textbook-format, in *Principles* I. His
metaphysics sought to answer such questions as: How does the human
mind acquire knowledge? What is the mark of truth? What is the actual
nature of reality? How are our mental experiences related to our
bodies and brains? Is there a benevolent God, and if so, how can we
reconcile his existence with the facts of illness, error, and immoral
actions?


### 3.1 How do our minds know?



Descartes had no doubt that human beings know some things and are
capable of discovering others, including (at least since his
metaphysical insights of 1629) fundamental truths about the basic
structure of reality. Yet he also believed that the philosophical
methods taught in the schools and used by most of his contemporaries
were deeply flawed. Accordingly, the doctrines of scholastic
Aristotelian philosophy contained a basic error about how fundamental
truths, such as those in metaphysics, are obtained. He articulated
this error in the First Meditation, by saying (not in his own voice,
but in that of the reader): "Whatever I have up till now
accepted as most true I have acquired either from the senses or
through the senses" (7:18). He then challenged the veridicality
of the senses with the skeptical arguments of the First Meditation,
including the dream argument (that we might experience sensory images
while dreaming that are indistinguishable from waking experience) and
the argument that a deceptive God or an evil deceiver is causing our
sensory experience or causes us to err even when reasoning.



In the Aristotelian scheme against which Descartes was moving, all
knowledge arises through the senses, in accordance with the slogan
"There is nothing in the intellect that was not previously in
the senses" (7:75, 267). Similarly, orthodox scholastic
Aristotelians agreed that there is "no thought without a
phantasm," or an image. Descartes explained these convictions as
the results of childhood prejudice (7:2, 17, 69, 107; *Princ*.
I.71-3). As children, we are naturally led by our senses in
seeking benefits and avoiding bodily harms. As a result, when we grow
into adults we are "immersed" in the body and the senses,
and so we accept the philosophical view that the senses reveal the
nature of reality (7:38, 75, 82-3).



Although Descartes ultimately accepted the senses as a source of some
kinds of knowledge, he denied that they reveal the natures of
substances (7:83). Rather, the human intellect perceives the nature of
reality through purely intellectual perception. This means that, in
order to procure the fundamental truths of metaphysics, we must
"withdraw the mind from the senses" (7:4, 12, 14) and turn
toward our innate ideas of the essences of things, including the
essences of mind, matter, and an infinite being (God). Descartes
constructed the *Meditations* so as to secure this process of
withdrawal from the senses in Meditation I. Meditation II discovers an
initial truth, the *cogito* (7:25), elsewhere summarized as the
argument "cogito, ergo sum," or "I think, therefore
I am" (7:140). The *cogito* result is known with
certainty because it is "clearly and distinctly" perceived
by the intellect (7:35). Clear and distinct intellectual perception,
independent of the senses, is, then, the mark of truth (7:35, 62,
73).



Descartes unfolds a sequence of clear and distinct perception in
Meditations III-VI and again in *Principles* I-II.
We consider these results in Secs. 3.3-3.5. For now, let us
examine Descartes' thoughts about the senses as a source of
knowledge, different from pure intellect.



Descartes' conclusion in Meditation VI that the senses do not
reveal the "essential nature" of external objects (7:83)
differs from his position in the *Rules*. In that work, he
allowed that some "simple natures" pertaining to corporeal
things can be known through the images of the senses (10:383, 417). In
the *Meditations*, he held that the essence of matter is
apprehended by innate ideas, independently of any sensory image
(7:64-5, 72-3). To that extent, his position
post-*Rules* agrees with the Platonic tradition in philosophy.
But Plato denigrated the senses as a source of knowledge. Descartes
was not a full-blown Platonist in that he did not totally disparage
sensory knowledge.



Descartes assigned two roles to the senses in the acquisition of human
knowledge. First, he acknowledged that the senses are usually adequate
for detecting benefits and harms for the body. Their natural function
is "to inform the mind of what is beneficial or harmful for the
composite of which the mind is a part" (7:83), that is, for the
composite of mind and body. Here, he adopted a widely held conception
of sensory function within natural philosophy, also found in the
Aristotelian and medical literatures.



Second, he acknowledged an essential role for the senses in natural
philosophy. Older interpretive literature sometimes has Descartes
claiming to derive all natural philosophical or scientific knowledge
from the pure intellect, independent of the senses. But Descartes knew
full well that he could not do that. He distinguished between the
general principles of his physics and the more particular mechanisms
by which he explained natural phenomena such as magnetism or the
properties of oil and water. He claimed to derive the general
principles "from certain seeds of truth" that are innate
in the mind (*Disc*. 6:64). These include the fundamental
doctrine that the essence of matter is extension (*Princ*.
II.3-4, IV.203). For particular phenomena, he relied on
observations to determine their properties (such as the properties of
the magnet), and he acknowledged that multiple hypotheses about
subvisible mechanisms could be constructed to account for those
phenomena. The natural philosopher must, therefore, test the various
hypotheses by their consequences, and consider empirical virtues such
as simplicity and scope (*Disc*. VI; *Princ*.
IV.201-6). Further, Descartes knew that some problems require
measurements that rely on the senses, including determining the size
of the sun (*Med*. 7:80, *Princ*. III.5-6) or the
refractive indexes of various materials (*Met*. VIII).



Although Descartes recognized an important role for the senses in
natural philosophy, he limited that role by comparison with
Aristotelian epistemology. Many scholastic Aristotelians held that all
intellectual content arises through a process of intellectual
abstraction that starts from sensory images found in the faculty of
imagination. Mathematical objects are formed by abstraction from such
images. Even metaphysics rests on knowledge derived by abstraction
from images. Of course, they held that the intellect plays a crucial
role in abstracting mathematical objects or the essences of natural
things. By contrast, Descartes affirmed that the truths of mathematics
and metaphysics are grasped by the pure intellect operating
independently of the senses and without assistance from the
imagination.



As regards knowledge, Descartes accepted that in order to know
something you must not only represent it as true (e.g., "the
essence of matter is extension"), but you must also affirm its
truth and do so with some justification. In his scheme of mental
capacities, the intellect, as the faculty of representation, offers
content for judgment. A second mental faculty, the will (*Med*.
IV, *Princ*. I.32-4), affirms or denies the truth of that
content (e.g., asserts that the essence of matter is extension).



Not all content deriving from the intellectual faculty is
"pure." Purely intellectual content arises from innate
ideas without any accompanying brain processes. Other intellectual
acts require the presence of the body: sense perception, imagination,
and corporeal (body-involving) memory. The content of these acts is
less clear and distinct than that of pure intellect, and may indeed be
obscure and confused (as in the case of color sensations).
Nonetheless, the will can affirm or deny such intellectual content.
With clear and distinct purely intellectual perceptions, the will is
justified in affirming their truth. (As discussed in the next
subsection, no error can arise in these judgments.) For lesser degrees
of clarity and distinctness, care must be taken in what the will
affirms (*Med*. IV, *Princ*. I.66-70,
IV.205-6). (See Newman 2019.)



In sum, in considering Descartes' answer to how we know, classes
of knowledge differ in the degree of expected certainty. Metaphysical
first principles as known by the intellect acting alone should attain
absolute certainty. Practical knowledge concerning immediate benefits
and harms is known by the senses. Such knowledge needn't attain
absolute certainty; even so, it is usually accurate enough. Objects of
natural science are known by a combination of pure intellect and
sensory observation: the pure intellect tells us what properties
bodies can have, and we use the senses to determine which particular
instances of those properties bodies do have. For submicroscopic
particles, we must reason from observed effects to potential cause. In
these cases, our measurements and our inferences may be subject to
error, but with care we may hope to arrive at the truth.


### 3.2 The mark of truth and the circle



At the beginning of the Third Meditation, Descartes declares "I
now seem to be able to lay it down as a general rule that whatever I
perceive very clearly and distinctly is true" (7:35). Clarity
and distinctness of intellectual perception is the mark of truth.



In the fifth set of Objections to the *Meditations*, Gassendi
suggests that there is difficulty concerning



> 
> what possible skill or method will permit us to discover that our
> understanding is so clear and distinct as to be true and to make it
> impossible that we should be mistaken. As I objected at the beginning,
> we are often deceived even though we think we know something as
> clearly and distinctly as anything can possibly be known. (7:318)
> 



Gassendi has in effect asked how it is that we should recognize clear
and distinct perceptions. If clarity and distinctness is the mark of
truth, what is the method for recognizing clarity and
distinctness?



In reply, Descartes claims that he has already supplied such a method
(7:379). What could he have in mind? It cannot be the simple belief
that one has attained clarity and distinctness, for Descartes
acknowledges that individuals can be wrong in that belief (7:35, 361).
He offers this criterion: we have a clear and distinct perception of
something if, when we consider it, we cannot doubt it (7:145). That
is, in the face of genuine clear and distinct perception, our
affirmation of it is so firm that it cannot be shaken, even by a
concerted effort to call the things thus affirmed into doubt.



As mentioned in Section 3.1, Descartes held that any act of judgment,
such as the affirmation "I think, therefore I am,"
involves both the intellect and will. The intellect perceives or
represents the content of the judgment; the will affirms or denies
that content. In the face of genuine clarity and distinctness,
"a great light in the intellect" is followed by "a
great inclination of the will" (7:59). The inclination of the
will is so strong that it amounts to compulsion; we cannot help but so
affirm. Descartes maintains that unshakable conviction provides the
criterion of genuinely clear and distinct perception. Can't
someone be unshakable in their conviction merely because they are
stubborn? Assuredly. But Descartes is talking about a conviction that
remains unshakable in face of serious and well-thought out challenges
(7:22). To be immune from doubt does not mean simply that you do not
doubt a proposition, or even that it resists a momentary attempt to
doubt; the real criterion for truth is that the content of a
proposition is so clearly perceived that the will is drawn to it in
such a way that the will's affirmation cannot be shaken even by
the systematic and sustained doubts of the *Meditations*.
Perhaps because the process for achieving knowledge of fundamental
truths requires sustained, systematic doubt, Descartes indicates that
such doubt should be undertaken only once in the course of a life
(7:18; 3:695).



Even so, problems remain. Having extracted clarity and distinctness as
the criterion of truth at the beginning of the Third Meditation,
Descartes immediately calls it into question. He re-introduces an
element of the radical doubt from the First Meditation: that a
powerful God might have created him with "a nature such that I
was deceived even in matters which seemed most evident" (7:36).
Descartes therefore launches an investigation of "whether there
is a God, and, if there is, whether he can be a deceiver"
(7:36).



In the course of the Third Meditation, Descartes constructs an
argument for the existence of God that starts from the idea of an
infinite being. The argument is intricate. It invokes the metaphysical
principle that "there must be at least as much reality in the
efficient and total cause as in the effect of that cause"
(7:40). This principle is put forward as something that is
"manifest by the natural light" (7:40), which itself is
described as a cognitive power whose results are indubitable (7:38),
like clear and distinct perception (7:144). Descartes then applies
that principle not to the mere existence of the idea of God as a state
of mind, but to the content of that idea. Descartes characterizes that
content as infinite, and he then argues that a content that represents
infinity requires an infinite being as its cause. He concludes,
therefore, that an infinite being, or God, must exist. He then equates
an infinite being with a perfect being and asks whether a perfect
being could be a deceiver. He concludes: "It is clear enough
from this that he cannot be a deceiver, since it is manifest by the
natural light that all fraud and deception depend on some
defect" (7:52). (If you are concerned by the move from infinity
to perfection, consider that in Descartes' philosophical
landscape perfect meant complete, and infinitude is the highest degree
of completeness.)



The second and fourth sets of objections drew attention to a
problematic characteristic of this argument. In the words of
Arnauld:



> 
> I have one further worry, namely how the author avoids reasoning in a
> circle when he says that we are sure that what we clearly and
> distinctly perceive is true only because God exists. But we can be
> sure that God exists only because we clearly and distinctly perceive
> this. Hence, before we can be sure that God exists, we ought to be
> able to be sure that whatever we perceive clearly and evidently is
> true. (7:214).
> 



Arnauld here raises the well-known problem of the Cartesian circle,
much discussed in recent years.



In reply to Arnauld, Descartes claims that he avoided this problem by
distinguishing between present clear and distinct perceptions and
those that are merely remembered (7:246). He is not here challenging
the reliability of memory (Frankfurt 1962). Rather, his strategy is to
suggest that the hypothesis of a deceiving God can only present itself
when we are not clearly and distinctly perceiving the infinity and
perfection of God, because when we are doing that we cannot help but
believe that God is no deceiver. It is as if this very evident
perception is to be balanced against the uncertain opinion that God
might be a deceiver (7:144). The evident perception wins out and the
doubt is removed.



Scholars have debated whether the above response is adequate. Some
have constructed other responses on Descartes' behalf or have
found them embedded in his writings. One type of response appeals to a
distinction between the natural light and clear and distinct
perception, and seeks to vindicate the natural light without appeal to
God (Jacquette 1996). Another response suggests that, in the end,
Descartes was not aiming at metaphysical certainty concerning a
mind-independent world but was merely seeking an internally coherent
set of beliefs (Frankfurt 1965). A related response suggests that
Descartes was after mere psychological certainty (Loeb 1992). The
interested reader can follow up this question by turning to the
literature just cited (as also to Carriero 2008, Doney 1987, Hatfield
2006, and Newman 2019).



Building on his claim that clear and distinct perceptions are true,
Descartes seeks to establish various results concerning the nature of
reality, including the existence of a perfect God as well as the
natures of mind and matter (discussed more fully in Sec. 3.3). Here we
must ask: What is the human mind that it can perceive the nature of
reality? Descartes has a specific answer to this question: the human
mind comes supplied with innate ideas that allow it to perceive the
main properties of God (infinity and perfection), the essence of
matter, and the essence of mind. For readers in Descartes' day,
this claim would naturally raise a further question: assuming that
these innate ideas concern "eternal truths" about God,
matter, and mind, do these truths hold independently of God, or do
they instead derive from the original contents of God's own
intellect?



Descartes rejected both alternatives. He denied, along with many of
his contemporaries, that there are eternal truths independent of the
existence of God. But he departed from many of his contemporaries in
also denying that the eternal truths are fixed in God's
intellect. Some Neoplatonist philosophers held that the eternal truths
in the human mind are copies, or ectypes, of the archetypes in the
mind of God. Some Aristotelian philosophers just prior to Descartes,
including Francisco Suarez (1548-1617), held that the
eternal truths reflect God's own understanding of his creative
power; God's power includes that, if he creates a rabbit, it
must be an animal. Eternal truths are latent in God's creative
power, and he understands this, so that if human beings understand the
eternal truths as eternal, they do so by understanding the creative
power of God, which may be something beyond human capacity (Hatfield
1993).



Descartes had a different account. He held that the eternal truths are
the free creations of God (*Corr*. 1:145, 149, 151;
*Med*. 7:380, 432), originating from him in a way that does not
distinguish among his power, will, and intellect. God decides what the
essence of a circle is, or to make 2 + 3 = 5. He might have created
other essences, but we can't conceive what they might have been.
Our conceptual capacity is limited to the innate ideas that God has
implanted in us, and these reflect the actual truths that he created.
God creates the eternal truths (concerning logic, mathematics, the
nature of the good, the essences of mind and matter), and he creates
the human mind and provisions it with innate ideas that correspond to
those truths. Even in this scheme there must be some eternal truths
not created by God: those that pertain to the essence of God himself,
including his existence and perfection (see Wells 1982).


### 3.3 The nature of reality



Descartes reveals his ontology implicitly in the six Meditations, more
formally in the Replies to Objections, and in textbook fashion in the
*Principles* (esp. I.51-65). The main metaphysical
results that describe the nature of reality assert the existence of
three substances, each characterized by an essence. The first and
primary substance is God, whose essence is supreme perfection (Med.
7:46. 52. 54. 162; *Princ*. I.54). In fact, God is the only
genuine substance, that is, the only being that is capable of existing
on its own. The other two substances, mind and matter, are created by
God and can only exist through his ongoing act of preservation or
conservation, called God's "concurrence"
(*Princ*. I.51).



Descartes' arguments to establish the essences of these
substances appeal directly to his clear and distinct perception of
those essences. God is an infinite substance and the idea of God
includes necessary existence (*Med*. III, V, *Princ*.
I.14, 19). Descartes used this idea of God to fashion an argument for
the existence of God, now called the Ontological Argument (see Nolan
2021).



The essence of matter is extension in length, breadth, and depth. One
might speak here of "spatial extension," but with this
proviso: that Descartes denied the existence of space separate from
matter. Cartesian matter does not fill a distinct spatial container;
rather, spatial extension is constituted by extended matter (there is
no void, or unfilled space). This extended substance possesses the
further "modes" of size, shape, position, and motion.
Modes are properties that exist only as modifications of the essential
or principal attributes of a substance. In addition to its essence,
extension, matter also has the general attributes of existence and
temporal duration (these are shared with mind).



The essence of mind is thought. Minds have the principal attribute of
thinking, divided into the two chief powers or faculties previously
mentioned: intellect and will. The intellectual, or perceiving power
is further divided into the modes of pure intellect, imagination, and
sense perception. As mentioned in Section 3.3, pure intellect operates
independently of the brain or body, while imagination and sense
perception require the body for their operation. The will is also
divided into various modes, including desire, aversion, assertion,
denial, and doubt. These always require some intellectual content
(whether pure, imagined, or sensory) upon which to operate. Perhaps
for that reason, Descartes describes the mind as an
"intellectual substance" (*Med*. VI, 7:78; also,
7:12). The mind essentially has a will, but the intellectual (or
perceptive, or representational) power is more basic, as the
operations of the will depend on it.



What role does consciousness play in Descartes' theory of mind?
Many scholars believe that, for Descartes, consciousness is the
defining property of mind (e.g., Rozemond 2006). There is some support
for this position in the *Meditations* (Second Replies).
Descartes defines mind as "the substance in which thought
immediately resides" (7:161), and he says that the term
"thought" extends to "everything that is within us
in such a way that we are immediately conscious of it" (7:160\*).
If mind is thinking substance and thoughts are essentially conscious,
perhaps consciousness is the essence of thought?



Perhaps not. Descartes did hold that all thoughts are, in some way,
conscious (7:226), but this did not mean that we have reflective
awareness of, or notice, every thought that we have (*Corr*.
5:220). In the Second Meditation, he describes himself as a thinking
thing by enumerating all the modes of thoughts of which he is
conscious: understanding (or intellection), willing, imagining, and
(at this point, at least seeming to have) sense perceptions (7:28). He
thus sets up consciousness as a mark of thought. But is it the
essence? Not necessarily. If perception (intellection, representation)
is the essence of thought, then all thoughts might have basic
consciousness because the character of the intellectual substance is
to represent, and any representation present in an intellectual
substance is, thereby, present in mind. An intellectual substance (a
mind) is a perceiving substance, which intrinsically perceives its own
states. Further, he held that any act of will present in an
intellectual substance is thereby available to consciousness
(*Pass*. I.19). (On consciousness and the essence of mind, see
Jorgensen 2020, 2.1).



In distinguishing between conscious thoughts and thoughts of which we
are reflectively aware, Descartes allowed for conscious thoughts that
we don't notice or remember. Indeed, his theory of the senses
(Sec. 5) allows for unnoticed sensations and mental operations.


### 3.4 Mind-body relation



In the *Discourse*, Descartes presented the following argument
to establish that mind and body are distinct substances:



> 
> Next I examined attentively what I was. I saw that while I could
> pretend that I had no body and that there was no world and no place
> for me to be in, I could not for all that pretend that I did not
> exist. I saw on the contrary that from the mere fact that I thought of
> doubting the truth of other things, it followed quite evidently and
> certainly that I existed; whereas if I had merely ceased thinking,
> even if everything else I had ever imagined had been true, I should
> have had no reason to believe that I existed. From this I knew I was a
> substance whose whole essence or nature is simply to think, and which
> does not require any place, or depend on any material thing, in order
> to exist. (6:32-3)
> 



This argument moves from the fact that he can doubt the existence of
the material world, but cannot doubt the existence of himself as a
thinking thing, to the conclusion that his thoughts belong to a
nonspatial substance that is distinct from matter.



While this argument might secure the existence of a thinker, it does
not show that the thinker is not a material thing. That conclusion
fallaciously rests on conceivability based in ignorance. There is
nothing to preclude that the thinking thing is in fact a complex
material system. Descartes has merely relied on the fact that he can
doubt the existence of matter to conclude that matter is distinct from
mind. That argument doesn't work. From the fact that the Joker
cannot, at a certain moment, doubt the existence of Batman (because he
is with him), but he can doubt the existence of Bruce Wayne (who
might, for all the Joker knows, have been killed by the Joker's
henchmen), it does not follow that Bruce Wayne is not Batman. In fact,
he is Batman. The Joker is merely ignorant of that fact.



In the *Meditations*, Descartes altered the argument. In the
Second Meditation, he again asserted that he could doubt the existence
of matter but not the existence of himself as a thinking thing. But he
explicitly refrained from concluding that his mind was distinct from
body, on the grounds that he remained ignorant of his nature (7:27).
Then, in the Sixth Meditation, having established, to his
satisfaction, the mark of truth, he used it to support a positive
argument that the essence of mind is thought and that a thinking thing
is unextended; and that the essence of matter is extension and that
extended things cannot think (7:78). He based this argument on clear
and distinct intellectual perceptions of the essences of mind and
matter, not on the fact that he could doubt the existence of one or
the other.



This conclusion asserts the well-known substance dualism of Descartes.
That dualism has problems. As Princess Elisabeth of Bohemia, among
others, asked: if mind is unextended and matter is extended, how do
they interact? This problem vexed not only Descartes, who admitted to
Elisabeth that he didn't have a good answer (3:694), but it also
vexed Descartes' followers and other metaphysicians. It seems
that, somehow, mind and body must be brought into relation, because
when we decide (a mental act) to pick up a pencil, our arm (a physical
thing) actually moves, and when light hits our eyes, we mentally
experience the visible world. But how do mind and body relate? Some of
Descartes' followers adopted the position of occasionalism,
according to which God mediates the causal relations between mind and
body; mind does not affect body and body does not affect mind, but God
gives the mind appropriate sensations given the state of the body, and
he makes the body move by putting it into the correct brain state when
we decide (mentally) to pick up the pencil (see Lee 2020). Other
philosophers adopted other solutions, including the monism of Spinoza
and the pre-established harmony of Leibniz.



In the *Meditations* and *Principles*, Descartes did not
focus on the metaphysical question of how mind and body interact.
Rather, he discussed the functional role of mind-body union in
the economy of life. Our sensations serve us well in avoiding harms
and pursuing benefits. Pain-sensations induce us toward behaviors that
usually protect our bodily integrity. Pleasure leads us toward things
that are usually good for us. Our sense perceptions are reliable
enough for distinguishing objects that need distinguishing and for
navigating as we move about. As Descartes saw it, "God or
nature" set up these relations for our benefit. They are not
perfect. Sometimes our senses present things differently than they
are, and sometimes we make judgments about sensory things that extend
beyond the appropriate use of the senses.


### 3.5 God and sensory error



In discussing the mark of truth, Descartes maintained that the human
intellect is generally reliable because God created it. In discussing
the functioning of the senses to preserve the body, he explained that
God has arranged mind-body interaction so that our sensations
generally are conducive to the good of the body. Nonetheless, errors
occur. Our judgments about sensory things may be false, just as, more
broadly, human beings may make poor moral choices even though God has
given them a will that is intrinsically drawn to the good
(*Corr*. 1:366, 5:159, *Princ*. I.42). For example, we
may form the childhood habit of judging, with respect to our color
sensations, that the color we experience "resembles"
something in objects (the Aristotelian theory). Subsequent
philosophical reflection (perhaps instigated by reading Descartes) may
lead us to conclude that these judgments are unwarranted, because
color sensations are not clear and distinct but obscure and confused
(*Princ*. I.66-70). In other cases, our sense perceptions
may represent things as being a certain way when they are not.
Sometimes we feel pain because a nerve has been damaged somewhere
along its length, and yet there is no tissue damage at the place the
pain is felt. Amputees may feel pain as located in their fingers when
they have no fingers (*Princ*. IV.196).



Descartes responded to these errors differently. He explained
cognitive (judgmental) and moral errors as resulting from human
freedom (*Med*. IV). God provides human beings with a will, and
wills are intrinsically free. But we have finite intellects. Because
we are free, we can choose to judge in cognitive or moral situations
in which we do not have clear and distinct perceptions of the true or
the good. If human beings restricted their acts of will to cases of
maximum clear and distinct perception, they would never err. If we go
wrong, Descartes contends, we are responsible, because we might have
restricted our judgments to matters about which we have the certainty
of clear and distinct perception. The applicability of this solution
to the case of color sensations and resemblance is, however, not
apparent, as we may not have made a reflective choice when, as
children, we accepted the resemblance account of color experience. In
that case, we might become culpable only after reading and accepting
Descartes' arguments that color sensations are obscure and
confused and applying this finding to our habitual assertion of
resemblance.



Matters are different for specific errors of sensory representation,
such as the mislocation of pain. The senses depend on media and sense
organs and on nerves that must run from the exterior of the body into
the brain. God sets up the mind-body relation so that our
sensations are good guides in most circumstances. But the media may be
poor (the light may not be good), circumstances may be unusual (as
when a partially submerged stick appears bent), or the nerves may be
damaged (as with the amputee). In these cases, the reports of the
senses are misleading. Since God has set up the system of
mind-body union, shouldn't God be held accountable for the
fact that the senses can misrepresent how things are? Here Descartes
does not appeal to our freedom of judgment, for in fact we must often
use the senses in suboptimal cognitive circumstances when navigating
through life, with no opportunity for reflection and reasoned choice.
Rather, he points out that God was working with the finite mechanisms
of the human body (7:88), and he suggests that God did the best that
could be done given the type of parts needed to constitute such a
machine (extended parts that might break or be unusually perturbed).
It's not God's fault that a well-made bodily machine can
occasionally create sensations that misrepresent.



Some cases of sensory misrepresentation are clear-cut cases of error.
With the amputee, the pain seems to be in fingers that are not there.
The representational content (that the fingers are damaged) does not
match the world. Similarly, a partially submerged stick may look bent.
Even if we use our intellects to interpret the illusions or sensory
misrepresentations so as to avoid error by withholding judgment or
even by judging correctly (7:438), it remains clear that sensory
misrepresentation has occurred.



In other cases, Descartes describes the senses as providing material
for error, but it remains uncertain whether such error arises from
making unwarranted judgments on obscure and confused sensations or is
due to straightforward sensory misrepresentation. In the Third
Meditation, he describes sensations that were later called
"secondary qualities" (e.g., colors, sounds, hot and cold)
as "materially false." Scholars have difficulty
interpreting this notion. Descartes initially defines material falsity
as something that "occurs in ideas, when they represent
non-things as things" (7:43). He offers the idea of cold as an
example: our senses represent cold as a positive quality of objects,
but Descartes considers that cold may instead simply be the absence of
heat and so isn't a quality of its own. Accordingly, this case
should be assimilated to sensory misrepresentation: representing
things as they are not (representing cold as a quality when it is the
absence of a quality).



Descartes also offers a different gloss on the obscurity of sensory
ideas. He allows that such ideas may be "true" in the
sense of representing something positive in things, but that they may
do so in such a way that "the reality which they represent is so
extremely slight that I cannot even distinguish it from a
non-thing" (7:44). Accordingly, sensory ideas are not
misrepresentations, they are simply so obscure and confused that we
cannot tell what their representational content might be by
considering their experienced character, such as the phenomenal
character of cold or of color. We then precipitately make an erroneous
judgment that color sensations resemble their causes in objects.
(Metaphysics and natural philosophy are needed to tell us what our
color sensations obscurely represent: properties of object-surfaces
that reflect light a certain way--see Sec. 5.) "Material
falsity" arises from representations so obscure that they allow
room for mistaken judgments (e.g., about resemblance).



The issues surrounding the notion of material falsity in Descartes are
intricate but telling of his theory of mind and sensory
representation. Entrance to the literature can be gained through Wee
(2006), Brown (2006, Ch. 4), and Hatfield (2013).


## 4. The New Science



During Descartes' school days, there were signs that the
scientific conception of the universe was changing. Recall that
Galileo's discovery of the four moons of Jupiter was celebrated
at La Fleche in 1610 (see Galileo 1610). More generally,
Copernicus had, in the previous century, argued forcefully that the
sun, not the earth, is at (or near) the center of the solar system
(Copernicus 1543). Early in the seventeenth century, Johannes Kepler
(1604) announced new results in optics, concerning the formation of
images, the theory of lenses, and the fact that the retinal image
plays a central role in vision. By the early 1630s, Descartes was
aware of William Harvey's claim that the blood circulates in the
body (*Corr*. 1:263).



Descartes contributed new results to the mathematical description of
nature, as developer of an accurate model of the rainbow
(*Met*. VIII) and as a discoverer of the sine law of
refraction. (Descartes was the first to publish the sine law, in
*Diop*. II. Previously, the law had been discovered by the
Islamic investigator Ibn Saul [10th c.], the English astronomer Thomas
Harriot [ca. 1600], and the Dutch mathematician and astronomer
Willebrord Snell [ca. 1620]. See Sabra 1967, 99-103, and Rashed
1990.) As significant as these results are, his primary contribution
to the "new science," or the "new mechanical
philosophy," lay in his general vision of a mechanistic approach
to nature, together with many details of that vision for specific
natural phenomena (such as magnetism, the formation of the solar
system, and sensory physiology), so as to provide a comprehensive
alternative to the dominant Aristotelian physics. The process of
forming a new science continued after Descartes, reaching a high point
in Newton's mechanics, including a consolidation of the
Copernican hypothesis.



In the textbooks of Aristotelian physics of Descartes' day, it
was common to divide physics into "general" and
"special." General physics pertained to the basic
Aristotelian principles for analyzing natural substances: form,
matter, privation, cause, place, time, motion. Special physics
concerned actually existing natural entities, divided into inanimate
and animate. Inanimate physics further divided into terrestrial and
celestial, in accordance with the Aristotelian belief that the earth
is at the center of the universe and differs in nature from the
heavens (including the moon, and everything beyond it). Inanimate
terrestrial physics first covered the four elements (earth, air, fire,
and water), then the "mixed" bodies composed from them,
including the various mineral kinds. Animate terrestrial physics
concerned the various powers that Aristotelians ascribed to ensouled
beings, where the soul is considered as a principle of life
(possessing vital as well as mental or cognitive powers). In the
simplest textbooks, the powers of the soul were divided into three
groups: vegetative (including nutrition, growth, and reproduction),
which pertained to both plants and animals; sensitive (including
external senses, internal senses such as memory and imagination,
appetite, and motion), which pertains only to animals, both nonhuman
and human; and rational powers, pertaining to human beings alone. All
the bodies in both inanimate and animate terrestrial physics were
governed by a "form" or active principle, as described in
Section 1.3.



Descartes' ambition was to provide replacements for all the main
parts of Aristotelian physics. In his physics, there is only one
matter and it has no active forms. He dissolved the boundary that made
celestial and terrestrial differ in kind. His one matter possesses the
properties of size, shape, position, and motion; it is infinitely
divisible and constitutes space (see Sec. 3.3). This matter is
governed by three laws of motion, including a precursor to
Newton's law of inertia (but without the notion of vector
forces) and a law of impact. Descartes' matter possessed no
"force" or active agency; the laws of motion as decreed by
God were sustained by his activity. Earth, air, fire, and water were
simply four among many natural kinds, all distinguished simply by the
characteristic sizes, shapes, positions, and motions of their
parts.



Although Descartes nominally subscribed to the biblical story of
creation, in his natural philosophy he presented the hypothesis that
the universe began as a chaotic soup of particles in motion and that
everything else was subsequently formed as a result of patterns that
developed within this moving matter (*Princ*. III.45; also
*Disc*. V, 6:45). Thus, he conceived that many suns formed,
around which planets coalesced. On these planets, mountains and seas
formed, as did metals, magnets, and atmospheric phenomena such as
clouds and rain. The planets themselves are carried around the sun in
their orbits by a fluid medium that rotates like a whirlpool or
vortex. Objects fall to earth not because of any intrinsic
"form" that directs them to the center of the universe,
and also not because of a force of attraction or other
downward-tending force. Rather, they are driven down by the whirling
particles of the surrounding ether. All cases of apparent action at a
distance, including magnetism, must be explained through the contact
of particle on particle. Magnetism is explained by corkscrew-shaped
particles that spew forth from the poles of the earth and flow from
north to south or vice versa, causing magnetized needles to align with
their flow (*Princ*. IV.133-83). To explain magnetic
polarity, Descartes posited that the particles exiting from the south
pole are threaded in one direction and those from the north are
threaded oppositely (like the oppositely threaded spindles on bicycle
pedals). (On Descartes' physics, looking back from a
post-Newtonian conception of that discipline, see Slowik 2021.)



Descartes also wanted to provide an account of the formation of plants
and animals by mechanical causes (*Disc*. V, 6:44-45),
but he did not succeed in framing an account that he was willing to
publish (so that only portions of his physiology were revealed in the
*Discourse*, *Dioptrics*, *Meditations*,
*Principles*, and *Passions*). In writings that were
published only posthumously (in 1664), including the *Treatise on
Man*, he developed an extensive physiological description of
animal bodies, in which he explained the functions of life in a purely
mechanical manner, without appeal to a soul or vital principle. (The
*Treatise on Man* was circulated in manuscript form during
Descartes' lifetime [5:112].) The *Description of the Human
Body* (1664) included his speculations on embryogenesis.



In mechanizing the concept of living thing, Descartes did not deny the
distinction between living and nonliving, but he redrew the line
between ensouled and unensouled beings. In his view, among earthly
beings, only humans have souls. He thus equated soul with mind: souls
account for intellection and volition, including conscious sensory
experiences, conscious experience of images, and consciously
experienced memories. He regarded nonhuman animals as machines, devoid
of mind and consciousness, and hence lacking in sentience. (Although
Descartes' followers understood him to have denied all feeling
to animals, some recent scholars question this interpretation; on this
controversy, see Cottingham 1998 and Hatfield 2008.) Consequently,
Descartes was required to explain all of the powers that Aristotelians
had ascribed to the vegetative and sensitive soul by means of purely
material and mechanistic processes (*Man* 11:202). These
mechanistic explanations extended not merely to nutrition, growth, and
reproduction, but also to the functions of the external and internal
senses, including the ability of nonhuman animals to respond via their
sense organs in a situationally appropriate manner: to approach things
that are beneficial to their body (including food) and to avoid danger
(as the sheep avoids the wolf).



In the *Treatise on Man* and *Passions*, Descartes
described purely mechanical processes in the sense organs, brain, and
muscles, that were to account for the functions of the sensitive soul.
These processes involved "animal spirits," or fine fluid
matter as distilled from the blood at the base of the brain and
distributed down the nerves to cause muscle motions in accordance with
current sensory stimulation. The brain structures that mediate
behavior may be innate or acquired. Descartes ascribed some things
that animals do to instinct; he explained other aspects of their
behavior through a kind of mechanistic associative memory. He regarded
human physiology as similar to nonhuman animal physiology, anent both
vegetative and (some) sensitive functions--those sensitive
functions that do not involve consciousness or intelligence:



> 
> Now a very large number of the motions occurring inside us do not
> depend in any way on the mind. These include heartbeat, digestion,
> nutrition, respiration when we are asleep, and also such waking
> actions as walking, singing, and the like, when these occur without
> the mind attending to them. When people take a fall, and stick out
> their hands so as to protect their head, it is not reason that
> instructs them to do this; it is simply that the sight of the
> impending fall reaches the brain and sends the animal spirits into the
> nerves in the manner necessary to produce this movement even without
> any mental volition, just as it would be produced in a machine.
> (Fourth Replies to Objections, *Med*. 7:229-30)
> 



Much human behavior occurs without intervention from the mind.



The fact that Descartes offered mechanistic explanations for many
features of nature does not mean that his explanations were
successful. His followers and detractors debated the success of his
proposals for nearly a century after his death. His accounts of
magnetism and gravity were challenged. Leibniz questioned the
coherence of Descartes' laws of motion and impact. Newton
offered his own laws of motion and an inverse square law of
gravitational attraction. His force-based account of orbital planetary
motions replaced Descartes' vortexes. Others struggled to make
Descartes' physiology work. There were also deeper challenges.
Some wondered whether Descartes could explain how his infinitely
divisible matter coalesces into solid bodies. Why shouldn't
collections of particles act like puffs of smoke, that separate upon
contact with larger particles? Indeed, how do particles themselves
cohere?



Such problems were real, and Descartes' physics was abandoned
over the course of the eighteenth century. Nonetheless, it provided a
conception for a comprehensive replacement of Aristotelian physics
that persisted in the Newtonian vision of a unified physics of the
celestial and terrestrial realms, and that continued in the
mechanistic vision of life as revived in the nineteenth century. (On
the rise of the new science, or what is sometimes called the
"scientific revolution," see Henry 2008 and Shapin 1996;
for a survey of Descartes' natural philosophy, see Gaukroger
2002.)


## 5. Theory of Sense Perception



As the "mechanical philosophy" of Descartes and others
replaced the Aristotelian physics, the theory of sensory qualities
required revision. This was especially true for what came to be known
as the "secondary qualities" (in the terminology of Robert
Boyle and John Locke). The secondary qualities include colors, sounds,
odors, tastes, and tactile qualities such as hot and cold. The
Aristotelians maintained that these qualities exist in objects as
"real qualities" that are like instances or samples of the
quality as experienced. A red thing possesses the quality red in just
the same way it possesses a shape: it simply is red, and we experience
that very redness when we see a red object (the "resemblance
thesis" from Sec. 3.5).



Descartes sought to replace "real qualities" with a
mechanistic account of qualities in objects. The sensory qualities of
objects would be explained by what were later called "primary
qualities" (such as size, shape, position, and motion).
Accordingly, Descartes rendered light as a property of particles and
their motions: it is a "tendency to move" as found in a
continuous medium and radiating out from a luminous body. When light
strikes an object, the particles that constitute light alter their
rotation about their axis. "Spin" is what makes light have
one color rather than another. When particles with one or another
degree of spin interact with retinal nerves, those nerves jiggle in a
certain way. In the brain, this jiggling affects the animal spirits,
which in turn affect the mind, causing it to experience one or another
color. Color in objects is thus that property of their surface that
causes light particles to spin in one way or another, and hence to
cause one sensation or another (*Diop*. I, 6:85, 91-2).
Sound arises from vibrations in sounding things, and odor from shaped
particles that differentially affect the olfactory nerves.



Descartes introduced this new theory of sensory qualities in the first
six chapters of *Light*. He defended it by arguing that his
explanation of qualities in bodies in terms of size, shape, and motion
are clearly understood by comparison with the Aristotelian qualities
(11:33). Subsequently, in the *Meditations* and
*Principles*, he supported this account by appeal to the
metaphysical result that bodies possess only geometrical modes of
extension (*Med*. V, *Princ*. I.69, II.4-5,
IV.199). Real qualities are ruled out because they are not themselves
instances of size, shape, or motion (even if patches of color have a
size and a shape, and can be moved about).



In addition to a new theory of sensory qualities, Descartes offered
theories of the way in which the spatial properties--size, shape,
distance, and position--are perceived in vision. In
Descartes' day and before, "optics" was defined as
the theory of vision, including physical, physiological, and
psychological aspects. In antiquity, Euclid and Ptolemy wrote on
optical problems. During the Middle Ages, the Arabic natural
philosopher Ibn al-Haytham produced an important new theoretical work
on vision that included an extensive account of the perception of
spatial properties.



The theoretical terrain in optics changed with Kepler's doctrine
that vision is mediated by the retinal image and that the retina is
the sensitive body in the eye. Previous theorists generally believed
that the "crystalline humor," now known as the lens, was
the sensitive body. Descartes accepted Kepler's result and
framed a new theory of spatial perception. Some of his theorizing
simply adapted Ibn al-Haytham's theories to the newly discovered
retinal image. Ibn al-Haytham held that size is perceived by combining
the visual angle that a body subtends with perception of its distance,
to arrive at a perception of the true size of the object. (Visual
angle is formed by the directions from a vantage point to a
seen-object for a given fixation, e.g., the angle formed by the
direction to the feet and to the crown of the head of a person
standing at moderate distance to us.) In Ibn al-Haytham's
scheme, visual angle is registered at the surface of the crystalline
humor. Descartes held that size is perceived by combining visual angle
with perceived distance, but he now treated visual angle as the extent
of an object's projection onto the retina. (On spatial
perception from Euclid to Descartes, see Hatfield 2020.)



In Ibn al-Haytham's account, if the size of an object is known,
distance may be perceived through an inference; for a given size, an
object's distance is inversely proportional to its visual angle.
Descartes recognized this traditional account (*Diop*. VI,
6:138-40), depending as it does on past experience of an
object's size and on an inference or rapid judgment that
combines perceived visual angle with this known or remembered size.
Descartes held that these judgments are habitual and happen so quickly
that they go unnoticed, as do the sensations that present visual
angle, being rapidly replaced by visual experiences of objects at a
distance (Sixth Replies, *Med*. 7:437-38).



Ibn al-Haytham further maintained that distance can be perceived by an
observer's being sensitive to the number of equal portions of
ground space that lie between the observer and a distant object.
Descartes did not adopt this explanation. However, Descartes used his
mechanistic physiology to frame a new account of how distance might be
perceived that drew on Kepler's results.



In the Keplerian theory of how the eye works, an image is formed on
the retina as a result of refraction by the cornea and lens. For
objects at different distances, the focal properties of the system
must be changed, just as the focal length of a camera is changed
(Kepler 1611, prop. 64). There were several theories of how this might
occur, and Descartes sometimes said merely that the shape of the eye
changes to accommodate for near and far vision (*Diop*. VI,
6:137), sometimes that specifically the shape of the lens changes
(*Man* 11:155-56, 159). He then theorized that this
change in the shape of the lens must be controlled by muscles, which
themselves are controlled by nerve processes in the brain.



Descartes realized that the central nervous state that controls
accommodation would vary directly in proportion to the physical
distances of objects. However, unlike the case of inferring distance
from known size and visual angle, Descartes did not suppose that the
mind is aware of the apparatus for controlling the accommodation of
the eye. Rather, he supposed that the central brain state that varies
with distance directly causes an idea of distance in the mind, by an
"institution of nature," which is innate (*Diop*.
VI, 6:137\*; see also *Man* 11:183). An institution of nature is
a relationship between characteristics of brain activity and a
resulting idea or sensation. In this case, the brain state controlling
accommodation causes the idea (sensation or perception) of distance.
Such institutions also link characteristic brain states with color
sensation (*Diop*. VI, 6:130; see Mantovani 2022).



When we correctly perceive the distance and combine it with visual
angle (by an unnoticed mental act), the result is a veridical
perception of a size-at-a-distance. Descartes described the resulting
perception as possessing the attributes that were labelled "size
constancy" in the twentieth century:



> 
> Concerning the manner in which we see the size and shape of objects, I
> need not say anything in particular since it is included in the way we
> see the distance and position of their parts. That is, we judge their
> size by the knowledge or opinion that we have of their distance,
> compared with the size of the images they imprint on the back of the
> eye--and not simply by the size of these images. This is
> sufficiently obvious from the fact that the images imprinted by
> objects very close to us are a hundred times bigger than those
> imprinted by objects ten times farther away, and yet they do not make
> us see the objects a hundred times larger; instead they make the
> objects look almost the same size, at least if their distance does not
> deceive us. (*Diop*. VI, 6:140)
> 



When Descartes speaks of taking into account the "size of the
images" on the retina, he need only be speaking of visual angle,
which is equivalent to retinal-image size. In saying that a nearby
object is a hundred times larger on the retina than one ten times
farther away, he is speaking of area; the nearby object would be ten
times larger in linear height. If visual angle and object distance are
correctly perceived and combined, the object's constant true
size is perceived. If we get the distance wrong, as in underperceiving
the distance to the sun and moon, we misperceive the size, in this
case, as too small (*Diop*. VI, 6:144-45).



Descartes' work on visual perception is but one instance of his
adopting a naturalistic stance toward conscious mental experience. The
*Passions* constitute another (Sec. 6). It is sometimes said
that Descartes' dualism placed the mind outside nature by
rendering it as an immaterial substance. That is a retrospective
judgment from a perspective in which immaterial substances are
automatically deemed "unnatural." For Descartes and his
followers, mind-body interaction and its laws were included
within the domain of natural philosophy or physics (in the general
meaning of the latter term, as the theory of nature). Descartes spoke
of regular relations between brain states and the resulting sensory
experiences, which his followers, such as Regis, subsequently deemed
"laws" of mind-body relation (see Hatfield 2000). In
this way, Descartes and his followers posited the existence of
psychophysical or psychophysiological laws, long before Gustav Fechner
(1801-1887) formulated a science of psychophysics in the
nineteenth century.


## 6. Passions and Emotions



The passions and emotions had been a topic of philosophical interest
since antiquity and were much discussed in Descartes' day (James
1997). His own interest intensified during the 1640s, as a result of
his correspondence with Princess Elisabeth (trans. Shapiro, 2007).
Descartes recognized two separate types of mental states that can be
classified as emotions (excitations) of the soul: purely intellectual
feelings, such as the intellectual joy of loving God, and
body-dependent affects on the mind, called "passions" (in
the etymological sense of the mind being passive in receiving them).
We will focus on the latter, which are the subject of Descartes'
final publication, the *Passions of the Soul* (1649). In the
preferatory letters to this work, Descartes acknowledged that he
approaches the passions "as a physicist" or natural
philosopher (11:326); but he in fact engaged to some extent all the
main genres of writings on the passions: medical, natural
philosophical, and moral.



Recall that Descartes attributed only two powers to the mind:
intellect and will. The intellect is the seat of ideas or perceptions,
which are representations. The will is an active power that responds
to the represented content, by affirming its truth, denying its truth,
doubting it, or desiring it to be the case. The will performs acts
such as choosing to think about mathematics or to raise one's
arm (*Princ*. I.32, *Pass*. I.17-19).



In the *Passions* (I.22-29), Descartes divided the
perceptions of the intellect that are caused by the body into three
kinds: perceptions of external objects (such as a candle or a bell);
perceptions of internal bodily states (such as hunger or thirst); and
perceptions that we refer to the soul itself, such as bodily love,
hate, and desire. These passions are "bodily" because it
is part of their definition that they have a bodily cause (as opposed
to purely intellectual emotions, which have the soul as cause,
*Pass*. I.91, 147). This third type of bodily passions can be
called the "passions proper."



Descartes defined the passions proper as "perceptions or
sensations or emotions of the soul that we refer particularly to it
and that are caused, maintained, and strengthened by some movements of
the spirits" (*Pass*. I.27). Like external sensations,
the passions are immediately caused by brain activity (animal
spirits). But they are referred to the soul, not to an external
object, even if they are in many cases triggered by an external
object. Suppose that we see a ferocious animal. The sense of vision
gives us a perception of the shape, size, and color of the animal,
according to the ways in which the nerves are affected and cause
animal spirits to flow (see Sec. 5). But the flow of animal spirits
also causes us to experience the passion of fear. Interestingly,
Descartes did not hold that we then run from the animal because we
experience the fear. Rather, the same flow of spirits that causes us
to feel fear also, at the same time, by purely mechanical processes
(see Sec. 4), affects the muscles of the legs so as to make us run.
This occurs "witout any contribution from the soul"
(*Pass*. I.38). The function of the experienced passion (the
feeling of fear) is to "move and dispose the soul to want the
things for which they prepare the body" (I.40; see also II.52),
in this case, to make us want to continue running.



The passions do not respond to all the properties that affect the
external senses. That is, "the objects which stimulate the
senses do not excite different passions in us because of all the
differences in them, but only because of the various ways in which
they may harm or benefit us, or in general have importance for
us" (*Pass*. II.52). Felt fear responds to the ferocious
animal under the aspect of potential harm. Descartes recognized six
simple or primitive passions: wonder, love, hatred, desire, joy, and
sadness (II.69), from which all the other passions are generated.
Wonder arises when we perceive something that is novel. Rare objects
affect the brain differently than objects we have seen before. The
resulting brain state causes the body to stay physically focused on
the novel object. The experienced passion of wonder then causes us to
focus mentally on the same object (II.70-78). The inclusion of
wonder as a primitive type of passion was new (or newly made
prominent) in the *Passions*.



The other five passions present objects as good or bad for us. The
passion of love makes us want to join ourselves willingly with its
object; hatred makes us want to separate ourselves. Desire is a
future-oriented feeling of wanting something it represents as good to
be the case. Joy arises from the present possession of a good thing;
sadness arises when an evil is represented as pertaining to us
(II.78-93). Again, these passions are caused by brain states
that arise in the machine of the body. States arise in the brain which
then prepare the body for behaviors and cause the felt passion. Here,
Descartes speaks of brain states as "representations";
joy, for example, "is a pleasant emotion that the soul has when
it enjoys a good that impressions in the brain represent to it as its
own" (II.91). The *Passions* relies heavily on the
mechanistic physiology in Descartes' earlier works.



Descartes' theory of the passions is complex and covers many
aspects, including the role of the brain, the role of judgment in
triggering passions, and the passions in morality. Entrance to the
literature can be found in Brown (2006), Rutherford (2021), Shapiro
(2003), and Hatfield (2007).


## 7. Reception and Legacy



The things that readers find valuable in Descartes' work have
changed across the centuries. His natural philosophy had an immediate
impact that lasted into the eighteenth century. His theory of vision
was part of that heritage, as were his results in mathematics. His
mechanistic account of the psychology of the sensitive soul and his
view that animals are like machines were revived in the nineteenth
century.



Descartes was strongly invoked in some works on the equality of the
sexes and the education of women. The seventeenth-century French
Cartesian Francois Poulain de la Barre used substance dualism
in arguing to the conclusion that "the mind has no sex"
(trans. Clarke, 157), although he was not above suggesting that female
physiology yields cognitive advantages (Schmitter 2018, 5). The early
eighteenth-century English philosopher Mary Astell used Cartesian
philosophy in her advocacy of education for women (Atherton 2001). In
contrast, Nicolas Malebranche was less favorable toward attributing
cognitive equality to women, showing that there was no single position
shared among the Cartesians concerning equality (Hamerton 2008). (For
entry into recent work on feminism and Descartes, including historical
studies, see Bordo 1999 and Schmitter 2018.)



The fortune of Descartes' metaphysics and epistemology is
complex. In his own time, he inspired a raft of followers, who sought
to develop his metaphysics, epistemology, and natural philosophy, and
to add a worked-out ethics. These authors included Geraud de
Cordemoy, Arnold Geulincx, Poulin de la Barre, Antoine Le Grand,
Malebranche, Regis, and Rohault. The British philosopher Henry More
had a long history of engaging with Descartes' mechanical
philosophy and metaphysics, toward which he at first expressed
qualified admiration, which later turned to deep hostility (More 1662,
1671; see Leech 2013). Pierre-Daniel Huet (1689) offered a scathing
critique of Descartes' philosophy. Other major philosophers,
including Benedict de Spinoza and G. W. Leibniz, were influenced by
Descartes' thought but developed their own, distinct
systems.



Descartes' project to examine the knower as a means to determine
the scope and possibilities of human knowledge had a profound effect
on early modern epistemology and metaphysics. Among his immediate
followers, Malebranche most fully developed this aspect of
Descartes' philosophy. Subsequent philosophers who were not
followers of Descartes also adopted the strategy of investigating the
knower. The epistemological works of Locke, George Berkeley, David
Hume, Thomas Reid, and Immanuel Kant pursued this investigation. These
authors came to different conclusions than had Descartes concerning
the ability of the human mind to know things as they are in
themselves. Hume and Kant especially--and each in his own
way--rejected the very notion of a metaphysics that reveals
reality as it is in itself. They did not merely deny Descartes'
particular metaphysical theories; they rejected his sort of
metaphysical project altogether. But they did so through the type of
investigation that Descartes himself had made prominent: the
investigation of the cognitive capacities of the knower.



During the twentieth century and into the twenty-first, various
aspects of Descartes' philosophy were widely invoked and perhaps
just as widely misinterpreted. The first is Descartes'
skepticism. In the early twentieth century, one response to the threat
of skepticism about our knowledge of the external world was to retreat
to the position that we can only know our own sense data, where
"sense data" are equated with the supposed contents of
immediate sensory experience: for vision, color patches having a shape
(e.g., Russell 1914). Some authors then treated Descartes'
project in the *Meditations* as that of reducing human
knowledge to immediate sense data, from which knowledge of the
external world was to be constructed. (A version of this reading is
Williams 1986.)



As a reading of Descartes, this position has little to offer. As we
have seen, in the Second and Third Meditations Descartes argues from
the indubitability of the *cogito* reasoning to the
trustworthiness of intellectual perception to the existence of a
perfect being (God). This argument does indeed seek to infer the
reality of a being external to the mind. But the inference does not
invoke sensory experience. It proceeds from a non-sensory and innate
idea of God to the existence of that God. Whatever one may think of
the quality of this argument, it has nothing to do with sense data.
Descartes used skeptical arguments as a tool to temporarily disengage
the reader from the sensory world in order to undertake metaphysical
investigations that rely on the pure intellect. But again, sense data
are not in the mix. The use of skepticism to "withdraw the mind
from the senses" (*Med*. pref., 7:9) may be read as an
instance of Descartes re-purposing, for his own philosophical ends, a
type of writing from his time: the spiritual exercise, now
reconfigured as cognitive exercises. Accordingly, Descartes'
meditator is guided by the text of *Meditations* in purging our
everyday reliance on the senses in order to uncover the pure intellect
(see Sec. 3.1). Recall that the metaphysical doubt is to be used once
in one's life in order to find the true metaphysics. The search
for absolute certainty supports this project and does not extend to
ordinary life (*Med*. I, VI, 7:22, 89-90). (On Descartes
and meditative writing, see Underkuffler 2019.)



Another line of twentieth- and twenty-first century interpretation
also focused on the isolation of the subject in the Second Meditation.
In the course of that Meditation, Descartes accepts that he knows the
contents of his mind, including putative sensory experiences, even
though he doubts the existence of his body. Some philosophers have
concluded from this that Descartes believed that human beings actually
can, in their natural state, have sensory experiences while lacking a
body. But Descartes rejected that possibility. In his metaphysics,
sense perception and imagination depend for their existence on
mind-body union. Purely intellectual perceptions do not depend
on the brain. But acts of imagination and sense perception require the
brain (*Pass*. I.19-20, 43). Descartes did allow that God
conceivably could produce sense experiences in us independent of the
brain; but because God's perfection is inconsistent with deceit,
he would never do this. In any event, in the natural case, human
sensations require a brain.



A third conception is little more than the use (or abuse) of Descartes
as a straw-man representative of a kind of over-arching "Western
rationality" that over-rationalized the human being and denied
the body and emotions. One recent version of this caricature suggests
that Descartes affirmed a "sense-represent-plan-move"
cycle in all explanations of human behavior (Wheeler 2005, Chap. 3).
As mentioned above, Descartes explained many human behaviors through
the machine of the body, without mental involvement. As he said in the
Fourth Replies, "When people take a fall, and stick out their
hands so as to protect their head, it is not reason that instructs
them to do this" (7:230); rather, the machine of the body
(material processes in the sense organs, brain, and muscles) produces
this behavior. Descartes envisioned similar purely mechanistic
explanations for many of the behaviors that arise with the passions or
emotions, in which the body acts first and the felt experience of the
passion serves to get the mind to want to do what the body is already
doing (*Pass*. I.37-40). Descartes by no means held that
all human behavior does or should arise from rational deliberation.
Which is not to say that he devalued rational deliberation when there
is time and need to undertake it. But he was under no illusion that
all effective human behavior stems from reason.



How could interpreters get Descartes so wrong? One recent explanation
suggests that many post-modern theorists have absorbed their Descartes
at second hand, and the same explanation might be extended to others
who invoke Descartes after only cursory engagement with his writings.
As the literary historian Michael Moriarty explains, leading French
theorists such as Jacques Lacan and Michel Foucault would have, in the
course of their French educations, "received a solid grounding
in philosophy, and in Descartes' works in particular"
(Moriarty 2003, 52). They then use Descartes as a stalking horse.
Moriarty suggests that many readers of Lacan and Foucault have not
received the same education in philosophy or in Descartes. Such
individuals, "who read Lacan or Foucault without, or before,
reading Descartes, thus imbibe a certain perception of Descartes, more
negative, perhaps, than the authors themselves, writing against the
grain of their own culture, may have intended to convey" (2003,
53). The implication is that Lacan and Foucault engaged Descartes from
a knowledge of his writings, whereas others who lack such knowledge
misunderstand the value of such genuine engagement and take away
misunderstood implications.



What is Descartes' legacy now? His influence on the seventeenth
century is historically permanent, including his specific
contributions in mathematics and optics, his vision for a mechanistic
physiology, and the model he offered to Newton of a unified celestial
and terrestrial physics that assigns a few basic properties to a
ubiquitous matter the motions of which are governed by a few simple
laws. In this regard, Descartes' work offers an example of
culturally engaged philosophy. Descartes had a sense for the
fundamental philosophical issues of his time, many of which concerned
the theory of nature and the attempt to found a new natural science.
He not only offered a systematic reformulation of the extant natural
philosophy, but he did so in a way that could be heard and
understood.



Beyond past historical influences, Descartes' philosophy
continues to speak to us now and to offer new insights to new
generations of philosophers who are in position to hear what he said.
This can be seen in the revival of body-first theories of the
emotions. (Ironically, some of Descartes' most vocal detractors
among scientists who study the emotions, including Damasio 1994,
espouse theories similar in many respects to Descartes' own, on
which, see Hatfield 2007.) Further, his theories of sensory qualities
have inspired new reflections (Simmons 2003), as has his account of
distance perception (see Wolf-Devine 1993 and the entries on optics
and perception in Nolan 2014). More generally, his
*Meditations* is one of the most finely crafted examples of
philosophical prose ever written. That in itself ensures its ongoing
value.



In the end, Descartes' legacy partly consists of problems he
raised, or brought into prominence, but did not solve. The
mind-body problem is a case in point. Descartes himself argued
from his ability clearly and distinctly to conceive mind and body as
distinct beings to the conclusion that they really are separate
substances. Most philosophers today accept neither the methodological
basis for his claim nor the claim itself. All the same, the
mind-body problem persists. In distinguishing the domain of the
mental from that of the physical, Descartes struck a chord. Many
philosophers accept the conceptual distinction, but remain uncertain
of the underlying metaphysics: whether mind is identical with brain;
or the mental emerges from complex processes in the brain; or
constitutes a property that is different from any purely physical
property, even while being instantiated by the brain. In this case, a
problem that Descartes made prominent has lived far beyond his
proposed solution.