## 1. Life



John Buridan was born around 1300 in or near the town of
Bethune in Picardy, France. He was educated in Paris, first at
the College Lemoine, where he was awarded a benefice or stipend
for needy students, and then at the University of Paris, where he
received his Master of Arts degree and formal license to teach by the
mid-1320s. He enjoyed a long and illustrious career as an arts master
at Paris, serving twice (in 1328 and 1340) as university rector and
supporting himself with numerous benefices. He last appears alive and
well in a document of 1358, where he is mentioned among a group of
masters adjudicating a territorial dispute between the English and
Picard nations (the Parisian student body at the time was organized
according to one's place of origin). He must have died shortly
thereafter because in 1361, one of his benefices was awarded to
another
 person.[1]



Such is the historical record--a handful of relatively minor
 details.[2]
 Buridan's fame as a teacher and philosopher, however, quickly
turned his life into the stuff of legend. There are stories that he
met his end when the King of France had him thrown into the Seine
River in a sack because of a scandalous affair with the Queen, that he
went on to found the University of Vienna after being expelled from
Paris for his nominalist teachings, and that he even hit the future
Pope Clement VI over the head with a shoe while competing for the
affections of the wife of a German shoemaker (the blow apparently
created the prodigious memory for which Clement was widely known). But
none of these stories can be independently verified, and most are
inconsistent with what we do know about
 him.[3]
 Nevertheless, they illustrate what the French scholar Edmond Faral
called the "*bruits de ville*" or
'buzz' surrounding Buridan's name in Parisian
circles, which continued for some time after his death (Faral 1950,
16).



Buridan's academic career was unusual in two respects, both of
which help to explain his philosophical outlook. First, he appears to
have spent his entire career in the faculty of arts, without moving on
to study for a doctoral degree in one of the more prestigious
faculties of law, medicine, or theology, which would have been the
more typical career path of a bright, literate, and upwardly-mobile
person in fourteenth-century Paris. Most of the figures we think of
today as medieval philosophers were in fact trained as theologians,
including Thomas Aquinas, Duns Scotus, and even William of Ockham
(though he did not finish his degree). Since university statutes
forbade arts masters from teaching or writing about theology, Buridan
produced no theological works and no commentary on the
*Sentences* of Peter Lombard, the principal genre of
philosophical writing in the fourteenth century.



Why did Buridan remain in the faculty of arts? It is unlikely that
someone of his obvious philosophical ability would have gone
unnoticed. Nor does the reason appear to have been a lack of means,
for despite his impoverished background he did receive a number of
bursaries and stipends, and is even listed in a document of 1349 as
being among those masters capable of supporting themselves without
financial assistance from the University. One possible
answer--though in the absence of concrete evidence that he never
studied theology, it must remain speculative--is that he
deliberately chose to remain among the 'artists
[*artistae*]'. What little he does say about philosophy
very clearly ties the philosophical enterprise to his office as an
arts master, not to whatever it was theologians took themselves to be
doing. Rejecting the traditional picture of theological learning as
the perfection or completion of philosophical wisdom, Buridan seems to
articulate, sometimes in spite of himself, a new vision of philosophy
as a secular enterprise based on what is evident to the senses and
intellect, in contrast to theology, which begins from non-evident
truths revealed in scripture and
 doctrine.[4]
 Perhaps most tellingly, Buridan never refers to theology as
constituting a '*scientia*', or body of
knowledge--an assumption theologians took great pains to defend
in their commentaries on the
 *Sentences*.[5]



Buridan is also different in that he remained for his entire life a
secular cleric rather than joining a religious order such as the
Dominicans or Franciscans. A papal letter of 1329 refers to him as
simply, "a cleric from the Diocese of Arras and Master of Arts
[*clericus Atrebatensis diocoesis, magister in artibus*]"
(Faral 1950, 11). By contrast, the best-known figures from the later
Middle Ages all had religious and intellectual affiliations beyond the
university: Thomas Aquinas was a Dominican friar, Duns Scotus and
William of Ockham were Franciscans, Gregory of Rimini was a member of
the Augustinian Order, and so on. Because he was religiously
unaffiliated, Buridan was free from the obligation to enter into the
doctrinal disputes that were arising with greater frequency and
intensity between theologians from different religious orders, as well
as between religious orders and the church hierarchy--e.g., the
dispute between the papacy and the Franciscans over apostolic poverty.
Thus, whereas Ockham spent his entire later career on political
crusades, away from philosophy, and was finally excommunicated for his
troubles, Buridan was bound only by the intellectual traditions and
pedagogical practices of his university. His confessional independence
also meant that he could occasionally help himself to philosophical
insights from a variety of sources. This emerges in the sometimes
eclectic character of his work, as we shall see below.


## 2. Writings



Most of Buridan's works are in the form of commentaries on
Aristotle. He wrote both *expositiones* (expositions), or
literal commentaries consisting of detailed, line-by-line explanations
of the meaning of Aristotle's words, and *quaestiones*
(questions), or longer, critical studies of the philosophical issues
raised by them, usually centered on a specific lemma from the text.
Both genres originated in the classroom, a fact which becomes clear in
occasional references to student queries and student concerns which
survive in the written versions. Like teachers in our own day, Buridan
lectured more than once on the same text over the course of his
career, with the result that there are sometimes different versions of
his commentary on the same work. For example, there are three versions
of his *Quaestiones* on Aristotle's *De anima*,
the last of which identifies itself as the "third or final
lecture [*tertia sive ultima lectura*]". Where there are
multiple versions of the same commentary, their relationship is
generally one of increasing length and sophistication over time.



Buridan commented on virtually all of the major works of Aristotle. In
addition to the entire *Organon*, there are commentaries on
Aristotle's *Physics*, *On the Heavens*, *On
Generation and Corruption*, *De Anima*, *Parva
Naturalia*, *Metaphysics*, *Nicomachean Ethics*, and
 *Rhetoric*.[6]
 He also wrote a number of shorter, independent treatises on
philosophical topics that were controversial in his day, such as the
*Tractatus de relationibus* [Treatise on Relations],
*Tractatus de universalibus* [Treatise on Universals],
*Tractatus de consequentiis* [Treatise on Consequences], and
*Quaestio de puncto* [Question on <the Nature of>
Points]. He was a very prolific author.



But Buridan's masterwork is the *Summulae de dialectica*
[Compendium of Dialectic], a comprehensive logic textbook which
started out as a commentary on the *Summulae logicales* or
logical compendium of the thirteenth-century dialectician, Peter of
 Spain,[7]
 but soon evolved into an independent work of astonishing breadth and
originality. In it, Buridan renovates the older medieval tradition of
Aristotelian logic through the *via moderna* [modern
way]--i.e., the newer, terminist logic which had gradually
replaced it. Because the work was accessible to master and student
alike, it became extremely popular at Paris and in newly-founded
universities at Heidelberg, Prague, Vienna, and across northern
Italy.



Buridan's other works were almost as widely read as the
*Summulae*. Handwritten copies and early printed editions were
carried by his students and followers throughout Europe, where they
were often used as primary texts in university courses on logic and
Aristotelian philosophy, meaning that arts masters would teach the
required books of Aristotle by reading and explaining Buridan's
commentary to the class. As a result, the *via Buridani*
continued to shape European thought well into the Renaissance.



Like many other medieval philosophers, Buridan's thought has not
been fully appreciated because of the lack of modern editions and
translations of his work (see
 bibliography).
 This situation began to improve with the appearance in 2001 of Gyula
Klima's mammoth translation of the entire *Summulae* from
the (now virtually complete) Latin critical edition of this text. More
recently, an edition of Buridan's commentary *On Generation
and Corruption* has appeared (Streijger, Bakker, & Thijssen
2010), along with editions of the first four books of his commentary
on the *Physics* (ed. Streijger & Bakker 2015, 2016), as
well as of his interesting commentary on pseudo-Albertus-Magnus'
treatise *De secretis mulierum* [On the Secrets of Women] (ed.
Beneduce 2017). We also now have an excellent English translation of
his groundbreaking *Treatise on Consequences* (tr. Read 2015),
as well as an edition and translation of his influential commentary on
Aristotle's *De Anima* (ed. & tr. Klima, Sobol,
Hartman, and Zupko 2023). Other editions and translations are being
planned or are currently in progress.



Thanks to the increasing availability of modern editions of not just
Buridan's writings but other fourteenth-century thinkers as
well, we are beginning to get a better picture of who influenced
Buridan. We know he had access to the *Summa Logicae* of
William of Ockham (Dewender 2016), although he never mentions Ockham
by name and his own *Summulae de Dialectica*, while certainly
inspired by Ockham's nominalist *via moderna*, frames its
teachings more traditionally in terms of the logic curriculum
presented in the *Summulae Logicales* of Peter of Spain.
Likewise, Book I, q. 8 of Buridan's *Physics* commentary
makes his opposition to the Ockhamist denial of quantitative forms
explicit, but there are almost certainly other authors in the mix
whose arguments Buridan is targeting, such as those of his Parisian
contemporary, Albert of Saxony (QP I.8; ed. Streijger and Bakker 2015:
79-92). Another author influencing Buridan's natural
philosophy is the English logician Walter Burley, who is mentioned by
name on several occasions. Buridan seems to have become acquainted
with the controversy on the intension and remission of forms via
Burley, though his own treatment of the problem in his commentaries on
the *Physics* and *On Generation and Corruption* appears
to be aimed at another Parisian contemporary, Nicole Oresme, who
adopted a modified version of Burley's view (Biard 2002; Caroti
2004). A surprising source for Buridan's lengthy
*Quaestiones* on the *Nicomachean Ethics* is the
*Nicomachean Ethics* commentary of Gerald of Odo, a Franciscan
theologian known for his opposition to Ockham (Walsh 1975; Dewender
2016). Buridan's *Nicomachean Ethics* commentary also makes
use of another surprising source, the Stoic teachings of Seneca the
Elder, which Buridan insists should be read not not as opposed to
Aristotelian ethics but as perfective of it (Walsh 1966; Zupko
2013).



Buridan was not just influenced by other philosophers. His writings on
physiology and psychology show that he was familiar with medical
texts, whose arguments he took seriously even though he is always
careful to distinguish medicine and philosophy as disciplines
(Beneduce 2023). Still, Buridan viewed medical learning as a way of
enhancing natural philosophy, so that philosophers and physicians
should be understood as talking about the same living phenomena.


## 3. Language



In the medieval university, arts masters provided students with their
basic education in grammar, logic or dialectic, and Aristotelian
philosophy, subjects that embodied the ideals of literacy and learning
in the Middle Ages. What they taught is perhaps best understood as a
specialized language of rational inquiry, which became the foundation
for further study in the faculties of law, medicine, and theology.
Students were required to learn, in ascending order, the exposition
and interpretation of authoritative texts (grammar), the structure and
modes of argumentative discourse (logic), and finally, the systematic
analysis and investigation of the order of nature (Aristotelian
philosophy). Although he did not write grammatical
 treatises,[8]
 Buridan asserts in the very first section of the *Summulae*
that "positive grammar [*grammatica positiva*] has to be
learned first, by means of which the master is able to communicate
with the disciple, whether it be in Latin, French, Greek, or Hebrew,
or whatever else" (S 1.1.1: 6). The disciple's knowledge
of logic and Aristotelian philosophy is built upon this grammatical
foundation.



The importance of language in Buridan's philosophy emerges on
many levels, all of which are driven by his pedagogical aims. In
logic, grammatical rules are explicitly subsumed as necessary
conditions of the science (*scientia*) of logic, so that
although the logician's notion of truth and the
grammarian's notion of congruence are separable in theory, in
practice the complete significance of a piece of discourse cannot be
determined without both. Context is crucial to interpretation:



> 
> We should also note that some might ask whether it is the composite or
> the divided sense that is properly expressed by 'Every man or
> (a) donkey runs', that is to say, whether only the term
> 'man' or the whole subject is distributed. And I say that
> we have to respond differently, in accordance with the different
> manners of speaking and writing. For if immediately after
> 'man' there is a sign of division, namely, a pause or a
> period, then the proposition will be called divided, and only
> 'man' will be distributed, but if not, then it will be
> called 'composite', and the whole subject will be
> distributed. (S 4.2.6: 250; cf. S 9.4, 15th sophism:
> 912-13).
> 



Accordingly, logic is not about some conceptually ideal or canonical
language but the practical art of interpreting human discourse:



> 
> an utterance [*vox*] does not have any proper import
> [*virtus propria*] in signifying and suppositing, except from
> ourselves. So by an agreement of the disputing parties, as in
> obligational disputes, we can impose on it a new signification and not
> use it according to its common signification. We can also speak
> figuratively [*transsumptive*] and ironically, according to a
> different signification. But we call a locution 'proper'
> when we use it according to the signification commonly and principally
> given to it, and we call a locution 'improper' when we use
> it otherwise, although we can legitimately use it otherwise. So it is
> absurd to say that a proposition of an author is false, absolutely
> speaking, if he puts it forth incorporating an improper locution,
> according to which it is true. Instead, we ought to say that it is
> true, since it is enunciated according to the sense in which it is
> true ... So it absolutely seems to me that wherever it is evident
> that an author puts forward a proposition in a true sense, although
> not as a proper locution, then to deny that proposition without
> qualification would be cantankerous and insolent [*dyscolum et
> protervum*]. But to avoid error, it should be properly pointed out
> that the proposition is not true in the proper sense, or by virtue of
> its proper meaning, and then it has to be shown in which sense it is
> true. (S 4.3.2: 256; cf. QIP 5: 144-145, ll. 800-829)
> 



In Buridan's view, the logician cannot expound the meaning of a
proposition without carefully attending to its internal features,
i.e., the sense of the particular locutions incorporated in it, as
well as to its external features, i.e., the discourse conditions that
surround it (see Zupko 2015).



This willingness to take human language as it is found, with all of
its ambiguities and rough edges, marks an important difference between
Buridan and Ockham, the fourteenth-century philosopher with whom he is
most often compared. Both make the traditional assumption that
propositions, be they spoken, written, or mental, are the bearers of
truth and falsity. Ockham, however, tends to see mental propositions
as logically ideal or, in modern parlance,
 'canonical'.[9]
 The problem with spoken and written propositions is that because they
depend on the meaning conventions of fallible users, they fail to be
universal and logically perspicuous. Thankfully, these shortcomings
can be filtered out metalinguistically once we realize that the
meanings of their constituent terms depend on their corresponding
mental concepts, which naturally signify the same for everyone. So in
Ockham's logic, the semantic relation between these concepts and
what they signify outside the mind is of paramount importance; spoken
and written terms have semantic properties too, of course, but in an
entirely derivative way. By contrast, Buridan never privileges
conceptual discourse or suggests that the logician might use it
systematically to reform spoken or written language. He holds that
spoken and written utterances--sometimes he uses the term
'utterance [*vox*]' where Ockham has 'term
[*terminus*]'--signify concepts primarily:
"the capability of speaking was given to us in order that we
could signify our concepts to others and also the capacity of hearing
was given to us in order that the concepts of speakers could be
signified to us" (S 4.1.2: 222). Accordingly, "utterances
are imposed to signify things only through the mediation of the
concepts by which those things are conceived" (QC 1: 4, ll.
45-6). Concepts are just the medium of signification for
Buridan, the cognitive or psychological aspect of the signification of
a word.



This difference helps to explain why Buridan uses paradoxes of
self-reference to test the functionality of his logic, whereas Ockham
avoids them by claiming that a term--or at least a term in those
circumstances--cannot refer to
 itself.[10]
 Buridan takes seriously the fact that people can and do utter
self-referential propositions, and thinks logicians should say what is
going on when they do. This is really a difference of perspective. As
Joel Biard has pointed out, we can divide medieval logicians into
those who try to restrict the possibilities of human discourse in the
direction of what is logically ideal, and those who are willing to
accept a proposition because it is grammatical and because the person
who utters it intends to signify something by it. Ockham, William of
Sherwood, and Walter Burley belong to the former group; Buridan and
Thomas Bradwardine to the
 latter.[11]
 It also explains why Buridan tells us that it is not possible to
analyze contradictory propositions unless they "have the same
subject and predicate in utterance and also in intention" (S
9.7, 2nd sophism: 943), and his reminding us that, when
testing a proposition for contradictoriness, "it is [sometimes]
necessary to add other utterances when contradicting it.... For
one should primarily attend to the intention, for we use words only to
express the intention" (S 9.8, 11th sophism: 979).
The logician must above all be a skilled interpreter of human
discourse.



For Buridan, linguistic confusion is the source of many of the
traditional problems of metaphysics and natural philosophy. His
approach is broadly nominalistic, but Buridan's nominalism is
more of a parsimonious way of doing philosophy than a doctrine about
the ontological or metaphysical status of universals. For example,
when a cause is understood as being actual rather than merely
potential, does our conception of it *qua* cause change in any
way? Aristotle leaves this ambiguous in *Metaphysics* V.2, but
some medieval philosophers thought it necessary to posit an additional
state of affairs to explain the dynamic aspect of causality, i.e., the
fact that a contingent state of affairs needs to be brought about by
some agent. Thus, if we think of God as the cause of Socrates, there
must be something else, God's-being-the-cause-of-Socrates
(*deum esse causam Sortis*), distinct from both God and
Socrates, to account for his existence. This 'something
else' then becomes not only what is signified by the proposition
'God is the cause of Socrates' (*complexe
significabile*), but also the proper object of our knowledge that
God is the cause of Socrates. Buridan replies by arguing that
philosophers who think this way do not know how to interpret human
discourse. They take everything too literally. But we should not be
misled by what a proposition literally says, or seems to say, into
thinking that there must be some new kind of entity corresponding to
God's being the cause of Socrates, especially since such
reifying moves do not help us to understand what is happening when a
cause actually causes (QM V.7-8: 30va-33ra).



The same sensitivity to questions of interpretation is evident in his
treatment of propositions in natural philosophy, where he argues that
we can meaningfully use propositions containing terms such as
'infinite [*infinitum*]' and 'point
[*punctum*]' to express actual states of affairs without
committing ourselves to the existence of infinite magnitudes or
indivisible points. The key is to realize that propositions do not
always wear their meanings on their sleeves. Their component terms can
be differently construed (e.g., categorematically or
syncategorematically), and can even perform different modal functions,
which, depending on how the proposition is read (e.g., in a composite
or divided sense) can change its truth
 conditions.[12]
 There will be ambiguities, of course, but Buridan is steadfast in his
assumption that the rational inquirer will always be able to sort them
out, given the right dialectical tools.


## 4. Logic



Following Aristotle and Porphyry, Buridan's logic is based on
two distinct, but complementary, conceptions of its purpose:
theoretical or pedagogical (*logica docens*) and practical
(*logica
 utens*).[13]
 The former, he says, is so called because "it teaches
[*docet*] us how, and from what [materials], arguments should
be constructed, whether those arguments be demonstrative, dialectical,
or of some other kind". The latter takes its name from the fact
that "it uses [*utitur*] arguments in order to prove
whether some conclusion is evident, regardless of the subject matter
of the conclusion" (QIP 1: 126-7, ll.176-80). But
since the teaching of logic is ordained to its use, Buridan holds that
logic is ultimately a practical rather than a speculative
discipline.



Historians of logic usually classify Buridan among the terminists or
'moderns', a diverse group of thirteenth and
fourteenth-century logicians who regarded the semantic properties of
terms (literally, the 'ends [*termini*]', or
subjects and predicates, of propositions) as the primary unit of
logical analysis. As we saw above, in addition to commenting on
Aristotle's *Organon*, he wrote a logical compendium, the
*Summulae de dialectica*, ostensibly as a commentary on Peter
of Spain's *Summulae logicales*, an influential terminist
textbook written a century earlier. But Buridan's
*Summulae* was essentially a new work, more that ten times
longer than the original and featuring many new and completely
rewritten sections. In it, Buridan leads his students and readers
through an orderly progression of teachings, beginning with
propositions (Treatise I), shifting down to the signification and
referential function of their component terms (II-IV), then back up to
terms and propositions insofar as they figure in more complex patterns
of reasoning: syllogisms (V), topics (VI), fallacies (VII), and
finally, demonstrations (VIII). The work concludes with a kind of
exercise book on paradoxical and otherwise puzzling propositions,
showing how they can be resolved using the techniques of the previous
eight treatises.



No encyclopedia article can do justice to the richness and variety of
Buridan's logic; it was interest in logic that first revived the
study of his work fifty years ago, and logic remains the one area in
which Buridan can speak directly to modern philosophical audiences.
The main reason for this is that Buridan's project of developing
a token-based semantics to ground his nominalist ontology is shared by
many philosophers of language today; likewise, the method of his
*Treatise on Consequences* has been rightly described by Hubert
Hubien as "very modern: we have here what is without doubt the
first attempt, albeit very imperfect, at an axiomatic exposition of
logic on the basis of the propositional
 calculus."[14]
 Nevertheless, this section will have the more modest aim of showing
showing how Buridan practiced the dialectical art and influenced logic
and semantics well into the sixteenth century.



First, Buridan did much to streamline and better articulate the
methods of terminist logic. The most important analytical tool in the
*Summulae* is the doctrine of *suppositio*
[supposition], which had been a feature of terminist logic for several
generations by the time Buridan arrived in Paris. Terms were thought
to possess two general semantic properties: signification, or what a
term 'makes known' in the mind of the person who sees it
or hears it or conceives of it, whether mediately or immediately
(thus, the written term 'Socrates' brings to mind the
concept of Socrates, which in turn signifies the actual person); and
supposition, which refers to the capacity of certain substantive terms
to stand for or 'pick out' something in a particular
context, such as in a proposition. Although the analogy is not
perfect, supposition performs many of the same functions as what we
would now call the theory of
 reference.[15]
 Traditional accounts divided supposition into proper supposition,
where a term is used with its typical or standard meaning, and
improper supposition, where a term is used in some metaphorical or
figurative sense. Most logicians went on to distinguish three kinds of
proper supposition: personal, where a term stands for what it
signifies (e.g., 'Socrates' in 'Socrates is a
man'); material, where it stands for itself (e.g.,
'man' in 'Man has three letters'); and simple,
where it stands for a common nature or concept (e.g.,
'man' in 'Man is a species'). Simple
supposition appears to have been a vestige of early terminist
 logic,[16]
 whose realist practitioners needed to distinguish between referring
to a universal thing and referring to a particular thing. But by the
fourteenth century, the whole notion of universals had become more
controversial, and nominalist logicians in particular were not about
to accept any special device for referring to them through common
terms such as 'man'. So simple supposition was readapted
to model reference to common concepts or intentions. Thus, Ockham
holds that a term exhibits simple supposition when it supposits
"for a concept in the mind [*pro conceptu
mentis*]," and is not being used
 significatively.[17]
 What united Ockham and his terminist predecessors was their
realization that if the proposition 'Man is a species' is
to be true, then the term 'man' cannot supposit personally
for any of the individual men it ultimately signifies, since it cannot
be said of any of them that he is a species (Socrates is a man, not a
species). Accordingly, the reference of 'man' must be to a
common nature or concept.



But Buridan contends that there are only two ways a term can stand for
something in a proposition, personally and materially:



> 
> Of the first [section on the divisions of supposition], we should
> realize that some people have posited also a third member, which they
> call 'simple supposition'. For they [e.g., Peter of Spain]
> held that universal natures are distinct from the singulars outside of
> the soul. And so they said that a term supposits personally when it
> supposits for the singulars themselves, that it supposits simply when
> it supposits for that material nature, and materially when it
> supposits for itself. But I hold that Aristotle correctly refuted that
> opinion in the seventh book of the *Metaphysics*
> [VII.3.1038b1-1039a23] and so this kind of supposition has to be
> eliminated, at least according to this interpretation. In another
> manner, others [e.g., Ockham] call supposition 'simple'
> when an utterance supposits for the concept according to which it is
> imposed and material when it supposits for itself or another similar
> to itself. And this can be permitted, but I do not care [about this
> usage], for I call both 'material supposition'. (S 4.3.2:
> 253)
> 



Buridan sees that it is misleading to assign a special logical sense
to terms being used to refer to themselves or to the concepts they
express, as if this were any different from figurative or metaphorical
usage, since only terms that refer to things existing *per se*
are being used in their proper sense. Thus, terms can stand either for
the things they ordinarily signify, in which case they supposit
personally, or for something else, in which case they supposit
materially. Material supposition applies whenever a term is used in
some way that departs from the meaning imposed upon it by the
linguistic community:



> 
> an utterance does not have any proper import [*virtus propria*]
> in signifying and suppositing, except from ourselves. So by an
> agreement of the disputing parties, as in obligational disputes, we
> can impose on it a new signification, and not use it according to its
> common signification. We can also speak figuratively
> [*transsumptive*] and ironically, according to a different
> signification. But we call a locution 'proper' when we use
> it according to the signification properly and principally given to
> it, and we call a locution 'improper' when we use it
> otherwise, although we legitimately can use it otherwise. So it is
> absurd to say that a proposition of an author is false, absolutely
> speaking, if he puts it forth incorporating an improper locution,
> according to which it is true. Instead, we ought to say that it is
> true, since it is enunciated according to the sense in which it is
> true. (S 4.3.2: 256)
> 



Notice that the default interpretation of a term is its proper sense,
defined as "the signification properly and principally given to
it". The proper signification of a term must be based on the
fact that "utterances were primarily and principally imposed to
signify so as to stand for their ultimate *significata*, and
not for themselves" (S 4.3.2:
 256);[18]
 that is to say, just as concepts (at least in the first instance)
naturally signify those extra-mental things that just as naturally
give rise to them, so spoken and written terms (at least in the first
instance) are imposed to signify, via their corresponding concepts,
the same ultimate
 *significata*.[19]
 For Buridan, this capacity is natural to us as creatures endowed with
the power of cognition. It is why he insists that determining the
nature of concepts pertains not to logic but to psychology or
metaphysics, speculative sciences whose conclusions cannot be
otherwise (QDI I.3:6, ll.
 4-10).[20]
 So even if we say that the proposition, 'Man is a
species' is true insofar as it is put forward in the context of
Aristotle's *Categories*, it is not literally true, or
true according to "the signification properly and principally
given to it", because of no *per se* existing man is it
true to say that he is a species. What happens is that when we work on
the *Categories*, we follow Aristotle's lead and depart
from conventional usage in such a way that the term 'man'
supposits not for individual men but for the universal concept
according to which it was imposed to signify, in which case the
proposition is true because "species and genera are universals
according to predication" (S 4.3.2: 254). So it can be true that
man is a species without it being *literally* true that man is
a species.



The second way in which Buridan changed the dialectical landscape was
to extend the range of traditional logic. There are numerous examples
of this, not all of which are uncontroversial because it is often hard
to tell what Buridan intended to achieve by a given innovation (this
goes for other medieval logicians as
 well).[21]
 But a fairly uncontroversial example can be found in his use of
supposition to examine the structure of certain complex terms that
would remain unanalyzed on the traditional account of syllogistic
inferences. Of particular importance here is the doctrine of
ampliation. Thus, although the syllogism, 'Nothing dead is an
animal, some man is dead; therefore, some man is not an animal',
is an acceptable fourth-mode syllogism of the first figure
(*Ferio*), Buridan denies that the consequence is
"formally valid". The reason is that in this syllogism,
'man' is an ampliative term, and "from an ampliated
nondistributed term the same term does not follow nonampliated"
that is, "in the minor proposition the term 'man'
was ampliated to past [things], whereas in the conclusion it was not
ampliated," making the premises true but the conclusion false (S
5.3.2: 326; cf. QAnPr I.14). Similarly, terms referring to the divine
persons sometimes generate counterexamples to the traditionally
accepted modes. Thus, "the following syllogism in
*Barbara* is invalid: 'Every God is the son, every divine
Father is God; therefore every divine Father is the Son", for
the transitivity of identity fails in cases "where the most
simple unity is a trinity of really distinct persons" (S 5.3.2:
327). Buridan also urges the reader to be wary of modal contexts
introduced by verbs of knowing and believing because "the verb
'know' ampliates the subject to supposit not only for
present things, but also for future and past ones". This means
that without suitable qualification, "although I know that every
man is an animal, nevertheless, it does not follow that every man is
known by me to be an animal; for then it would follow that every man,
whether alive or dead or yet to be born, would be known by me to be an
animal, which is false" (S 5.6.8: 348). What is noteworthy in
these and other examples is Buridan's use of the doctrine of
supposition to extend the range of 'truth-makers' for
modal inferences, e.g., in his assumption that "the presence of
a modal copula--*any* modal copula--in a proposition
ampliates the subject to stand for not only the actual things but also
the possible things that fall under that
 term".[22]
 Because it makes merely possible objects relevant to the evaluation
of modal inferences, ampliation can be seen as a kind of Buridanian
equivalent of possible worlds semantics, though it would be a mistake
to regard it as a remarkable anticipation of that twentieth-century
doctrine. Buridan's remarks on its theoretical significance are
 few,[23]
 and, despite the degree of technical sophistication involved, he
probably did not see it as a radical innovation, but as part of his
ongoing effort to make existing schemes for checking inferences more
practicable.



Third, and finally, Buridan made major contributions to certain forms
of logical inquiry that originated in the medieval period. Most modern
logicians know of his solutions to alethic paradoxes such as the Liar,
addressed in the eighth and final chapter of ninth treatise of the
*Summulae*, which belongs to the medieval literature of
*sophismata* or
 *insolubilia*.[24]
 The 7th sophism Buridan considers is 'Every
proposition is false'. The case posits "that all true
propositions are annihilated while the false ones remain [in
existence], and then Socrates propounds only this [proposition]:
'Every proposition is false'" (S 9.8, 7th
sophism: 965). The question is then asked whether Socrates's
proposition is true or false. The arguments on each side of the
question illustrate the difficulties one faces if 'true'
and 'false' are interpreted strictly. The argument that it
is false assumes that "it is impossible for the same proposition
to be true and false when propounded in the same language and
understood in the same way by everyone hearing it", and proceeds
to argue that the sophism is false because any proposition which
entails its own contradictory is impossible, and therefore false. The
opposite side begins by focusing on the logical form of the sophism as
a universal affirmative that has no counter-instance in the case at
hand, which stated that all true propositions have been annihilated
with only the false ones remaining. Second, the sophism must be true
because the subject and predicate terms supposit for the same things:
if every proposition is false, then each and every propositional
significate of the term 'every proposition' must be false,
as it indeed is, according to the case. Finally, the sophism must be
true because "it signifies only that every proposition is false;
and this is how things are [*ita est*]", according to the
case (S 9.8, 7th sophism: 965).



Buridan writes as if this particular sophism enjoyed some notoriety
among logic teachers at Paris, although all but one of the alternative
solutions he mentions were discussed and criticized from the very
beginning of the *insolubilia* literature. These involve
various *ad hoc* proposals that either build new assumptions
into the case or else make up new rules about how the terms of the
sophism are to be
 interpreted.[25]
 Into the first category falls a solution known as the
'*transcasus*', which involves the bizarre
suggestion that the time Socrates utters his proposition and the time
referred to by the verb of the proposition are not the same. This
would allow us to say that if there are no true propositions during
the first hour of a certain day, Socrates could utter his proposition
at the end of this hour and it would be true, where he is understood
as referring "not to the time at which he speaks but to the time
of that first hour". But this is of no help if we stick to the
case and assume that the times are the same. Alternatively, in a
solution advocated by the '*restringentes*
[restrictors]'--so-called because they avoided
self-reference by restricting what a term can supposit for--we
could make the proposition non-reflexive by stipulating that
"terms that are apt to supposit for propositions are not put in
propositions to supposit for the propositions in which they are put,
but for others". But Buridan rightly rejects this second
strategy as failing to take seriously our conventional understanding
of terms, for when one uses the term 'proposition', he
says, "one understands indifferently all propositions, indeed,
present, past, and future ones, his own as well as those of another
person". A moment's reflection should make it obvious that
"this solution is worth nothing: for what one understands, of
that he can speak [*quod aliquis intelligit, de hoc potest
loqui*]" (S 9.8, 7th sophism:
 966).[26]



Buridan's quick answer to the sophism is that Socrates's
proposition is false in the case at hand. But before moving on to his
final answer, he first discusses a solution described as being held by
some people, including
 himself.[27]
 This is that there is another condition, in addition to the
requirement that its terms stand for the same thing or things, which a
proposition must meet if it is to be true. A proposition must also
signify or *assert* itself to be true (S 9.8, 7th
sophism:
 967).[28]
 In her detailed analysis of this sophism, Fabienne Pironet has shown
that the text in which Buridan defends this earlier view is his
question commentary on Aristotle's *Posterior Analytics*,
where it is expressed in terms of the traditional formula that
"howsoever [a proposition] signifies, so it is
[*qualitercumque significat, ita est*]" (QAnPo
 I.10).[29]
 Now Buridan holds that all propositions satisfy this condition
trivially: "every proposition by its form signifies or asserts
itself to be true" (S 9.8, 7th sophism: 967). The
problem with self-referential paradoxes is that they also seem to
signify that they are false. Thus, although the proposition 'I
say what is false [*ego dico falsum*]' "signifies
itself to be true in some fashion, nevertheless this is not so
entirely, or howsoever it signifies [*licet aliqualiter sic
significat, non tamen totaliter vel qualitercumque ita est*].
Therefore it is false" (QAnPo I.10).



Unfortunately, this looks no less *ad hoc* than the
*transcasus* and restriction solutions he has just criticized.
Why shouldn't other propositions, besides the paradoxical ones,
be able to signify that they are false? Buridan does not say in his
commentary on the *Posterior Analytics*, and in the
*Summulae* he rejects his earlier view for the rather different
reason that it is false "that every proposition signifies or
asserts itself to be true" (S 9.8, 7th sophism: 968).
His argument is not exactly clear, but the problem appears to be
semantic: he cannot find an interpretation of the phrase 'itself
to be true [*se esse veram*]' in the supplementary
condition that will permit it to function as a general principle.
Consider the proposition 'A man is an animal [*homo est
animal*]'. If we understand it materially, i.e., as standing
for a proposition, then it will signify 'The proposition
"A man is an animal" is true', which is false
because it refers to second intentions (concepts or signs by means of
which we conceive of other concepts or signs as such), and the
original proposition refers to things (human beings and animals), not
concepts. But what if we say that a proposition signifies itself to be
true if it is taken significatively for the things or first
intentions, rather than materially? This will not work either, argues
Buridan, because then the affirmative proposition 'A man is a
donkey [*homo est asinus*]' would signify that a man is a
donkey, which is false because the subject term 'man' does
not supposit for anything (no human beings are
 donkeys).[30]
 Accordingly, we cannot base our solution to self-referential
paradoxes on the idea that every proposition signifies or asserts
itself to be
 true.[31]



The solution Buridan finally settles on receives the somewhat tepid
endorsement of being "closer to the truth" than the
previous solution--a reflection, perhaps, of his awareness of the
imperfectability of any formal system that tries to stick close to the
facts of human language. Here, the idea that a proposition formally
signifies itself to be true is replaced by the notion of implication
from the doctrine of consequences. "Every proposition," he
says, "virtually implies another proposition in which the
predicate 'true' is affirmed of the subject that supposits
for [the original proposition]" (S 9.8, 7th sophism:
 969).[32]
 Unlike the old solution, in which the second proposition is signified
by the first and hence part of its meaning, the new solution assumes
only that the second proposition follows logically from the first, so
that its meaning can be expounded separately. In this way, for the
truth of any proposition *P*, it is required not only (1) that
the subject and predicate terms of *P* stand for the same thing
or
 things,[33]
 but also (2) that *P* implies another proposition,
'*P* is true', which must also be true. Otherwise,
we would have a true antecedent and a false consequent, violating
Buridan's fifth theorem regarding assertoric consequences, which
states, "it is impossible for what is false to follow from what
is true [*impossibile est ex veris sequi falsum*]" (TC
I.8: 34, l. 97; Read (tr.) 2015: 77-78). Applying this to the
7th sophism, the constituent terms in the proposition
uttered by Socrates--'Every proposition' and
'false'--stand for the same things, since in the
posited case, "all true propositions are annihilated and the
false ones remain, and then Socrates propounds only this: 'Every
proposition is false'". So the first condition is
satisfied. But the implied proposition, '*P* is
true' (where *P* is the name of 'Every proposition
is false'), is false because its constituent terms, 'Every
proposition is false' and 'true', do not stand for
the same thing, since *ex hypothesi*, *P* stands for the
antecedent proposition 'Every proposition is false', not
for things that are true. But this gives us a true antecedent and a
false consequent, and so the consequence does not hold. Therefore, the
sophism is false.


## 5. Metaphysics



Buridan's metaphysics is thoroughly informed by his logic. He
tries wherever possible to apply the *Summulae*'s
analytical techniques to solve problems in speculative philosophy. His
approach is critical in the sense that he tends to view traditional
problems in metaphysics as based on confusions of logic or language.
For the same reason, his solutions are not original in the modern
sense of being without precedent, although they have few equals in
terms of their elegance and economy of expression. Where philosophical
argumentation is concerned, Buridan is a master craftsman.



Like most arts masters in fourteenth-century Paris, Buridan is careful
to dissociate the metaphysical questions he asks as a philosopher from
similar questions that might be asked by a theologian. Jurisdictional
disputes forced Parisian arts masters to be quite clear about how they
were approaching a
 problem,[34]
 although what we now identify as medieval philosophy was practiced by
both sides. As far as Buridan is concerned, much of the confusion over
the proper domains of metaphysics and theology stems from Aristotle
himself, who identifies three kinds of speculative science: physics,
mathematics, and theology (Aristotle, *Metaphysics*
VI.1.1026a18; XI.7.1064b1). In his question commentary on the
*Metaphysics*, he provides the standard medieval interpretation
of this passage, reading 'theology' as
'metaphysics' and differentiating the three sciences in
terms of how they treat their respective subjects: whereas the natural
philosopher considers things insofar as they are qualified by motion,
and the mathematician insofar as they are quantified by number, the
metaphysician considers them only insofar as they pertain to the
"concept of being [*ad rationem essendi*]" (QM
VI.2:
 34ra).[35]
 For the difference between metaphysics and theology, however, we need
to go to the very beginning of the commentary, where he offers the
following gloss of Aristotle's remarks:



> 
> It should also be noted that [when we ask whether metaphysics is the
> same as wisdom,] we are not comparing metaphysics to theology, which
> proceeds from beliefs that are not known, because although these
> beliefs are not known *per se* and most evidently, we hold
> without doubt that theology is the more principal discipline and that
> it is wisdom most properly speaking. In this question, however, we are
> merely asking about intellectual habits based on human reason, [i.e.,]
> those discovered by the process of reasoning, which are deduced from
> what is evident to us. For it is in this sense that Aristotle calls
> metaphysics 'theology' and 'the divine
> science'. Accordingly, metaphysics differs from theology in the
> fact that although each considers God and those things that pertain to
> divinity, metaphysics only considers them as regards what can be
> proved and implied, or inductively inferred, by demonstrative reason.
> But theology has for its principles articles [of faith], which are
> believed quite apart from their evidentness, and further, considers
> whatever can be deduced from articles of this sort. (QM I.2: 4ra-rb)
> 



The difference is that theologians take their principles
('*principia*' = (lit.) 'starting
points') from articles of faith rather than from what is evident
to the senses and intellect, as philosophers do. So it is possible for
the same question--e.g., about the limits of divine
omnipotence--to be raised in both domains, though it will have a
more creaturely orientation for the
 philosopher.[36]
 Buridan concedes *de jure* place of privilege to theology
because of its subject matter, but treats philosophy and theology as
*de facto* equivalent in the speculative realm. Metaphysics, or
philosophical wisdom, cannot be ordained by theology because its
methods, which are rooted in its principles, are different. Philosophy
is accordingly not inferior to theology, just
 different.[37]



With regard to the problem of
 universals,[38]
 Buridan does not so much create a new theory as show how our
theoretical commitments can be expressed with a minimum of ambiguity
and fuss. Like Ockham, he is a nominalist, although this term must be
used with caution in later medieval philosophy because of the modern
tendency to identify it with the denial of real universals. It must be
remembered that most fourteenth-century philosophers were nominalists
in this sense because they associated real universals with Plato,
whose views they knew only secondarily and took to be fully
discredited by Aristotle in Book I of the
 *Metaphysics*.[39]
 But medieval nominalism involved much more than rejecting Platonic
universals. Its history can be traced to twelfth-century disputes over
the reading of sacred texts, in which the techniques of logicians such
as Abelard were pitted against those of grammarians such as Peter
 Helias.[40]
 As these disputes evolved and matured, nominalism was gradually
absorbed into the teaching of philosophers working in the faculty of
arts, so that by Buridan's time, it is better to think of
nominalism as a practice, or way of doing philosophy, than a piece of
doctrine.



When Buridan considers questions such as "whether universals
actually exist outside the soul" (TDUI: 137), his remarks are
almost always aimed at clarifying the meaning of the term
'universal' with respect to other terms such as
'individual', 'particular', and
'singular'. His rejection of realism is expressed in the
claim that universal terms have no ultimate significate, i.e., nothing
outside the soul they can 'make known' as
 such.[41]
 Hence, an account is needed of what such terms mean. Here, it is
almost as if Buridan thinks there is something incomplete about
propositions where the term 'universal' occurs in the
subject position, for when confronted with them his first move is
always to tell us how the term 'universal' is properly
understood (QIP 3: 136, ll.
 477-488).[42]
 He argues further that the primary signification of
'universal' is 'predicable of many', which
makes it a term of second intention, or a term of terms, since only
terms are predicable (QIP 3: 135-136; 4: 139; TDUI:
 148).[43]
 The second-intentional status of the term 'universal' is
also evident in propositions, where it does not signify a
'what' but a 'how', i.e., how we conceive of
something--in this case how the term so designated is
"indifferent to many supposits," or individuals (TDUI: 59;
see Zupko
 2013b).[44]
 As we saw above, logic is the study of terms such as
'proposition' taken materially, signifying actual tokens
of the type (QDI I.1: 6). Moving from propositions to arguments,
Buridan insists that terms in the premises and conclusions of
demonstrative arguments must be taken as standing materially, i.e.,
for themselves in the particular discourse conditions which surround
them, rather than personally, for their extra-mental significates (QIP
1: 128, ll. 223-237). Likewise, the proximate object of
scientific knowledge is the actual demonstrated or demonstrable
conclusion rather than the state of affairs it signifies, although
Buridan is willing to concede that "the terms of those
demonstrable conclusions, or even the things signified by those
conclusions" might be considered "remote", or
secondary, objects of knowledge (QIP 1: 127, l.
 208-209).[45]
 Careful and systematic analysis is the best antidote for metaphysical
perplexity because the trouble usually begins with untutored persons
who use some word or concept without knowing what it actually
means.



On the question of universals, Buridan's main contribution is to
develop what Gyula Klima has nicely termed an "essentialist
nominalism", arguing for the reality of the natures underlying
our simple substance concepts. Ockham understood universality in terms
of the indifference involved in our act of cognizing universals, so
that despite our having had different particular experiences of
horses, say, we are able to form complex concepts that count as
universal provided they are able to represent all horses; crucially,
there is nothing of the substantial nature of a horse that is conveyed
via the senses to the intellect on Ockham's theory. Against
this, Buridan argues that substantial concepts cannot merely be
collections of complex, connotative concepts, because then we would
have the absurd conclusion that substantial terms are not substantial
terms, for the concepts according to which they were imposed to
signify would not be simple substance concepts:



> 
> Again, if the substantial concept of man were complex, then let us
> posit that it consists of three simple ones, namely, **a**,
> **b**, and **c**. Then, if no concept of substance is simple,
> **a** can only be a concept of accident, and the same goes for
> **b** and **c**; therefore, the whole combined from them would
> also be only a concept of accident, and not one of substance, for a
> whole is nothing over and above its parts. But this is absurd, namely,
> that the substantial concept of man should be nothing but a concept of
> accidents; therefore, etc. [QP I.4, ed. Streijger & Bakker: 36,
> ll. 3-9; tr. Klima 2009: 95]
> 



Buridan proceeds to identify four ways in which one can obtain one
simple cognition from another directly, or without any inference [QP
I.4, ed. Streijger & Bakker:
 36-37].[46]
 The details need not detain us here, but suffice it to say that the
"empiricist" side of Buridan's nominalism is always
leavened by Aristotelian naturalism, which he felt was needed to
combat skeptical arguments about scientific knowledge, and indeed,
about the very existence of substances--arguments Ockham never
had to confront.



It should be noted as well that Buridan's methods do not always
produce parsimonious results. To Ockham's basic ontology of
substances and qualities he adds quantities, and he is much more
willing than Ockham to talk about modes or ways of being when
confronted with recalcitrant phenomena. Thus, he argues that we must
treat the question of *how* something is distinctly from
*what* it is if we are to have a coherent understanding of
motion, especially since the Ockhamist view is forced to posit an
infinite succession of spatial qualities (QM V.9: 32va; QP II.3, ed.
Streijger & Bakker, 256-263; QP IV.11, ed. Streijger &
Bakker,
 299-305).[47]
 Likewise, in a famous passage, Buridan is driven by his own
experience to reject Ockham's explanation of condensation and
rarefaction as kinds of locomotion. Why, he asks, does he find himself
unable to compress further the air in a bellows which has been stopped
up at one end? Not because of its matter, since more matter could
exist in a much smaller space; nor because of the substantial form of
the air, which would fill a much smaller space once it has been
cooled; nor even because of the heat it possesses, since more heat
could exist in a much smaller space, such as at the end of a red-hot
poker. No, the air must have a distinct quantitative form or magnitude
preventing it from being moved. Against those who would do away with
this distinction, Buridan argues that "a distinct magnitude of
this sort has not been posited in vain, for we have been forced to
posit it by compelling arguments that make it seem as useful or even
more useful to natural philosophy than [the qualities of] whiteness or
blackness" (QP I.8, ed. Streijger & Bakker, 92, ll.
 3-6).[48]


## 6. Natural Philosophy



Later medieval natural philosophy included both the rich commentary
tradition on Aristotle's *Physics*, as well as treatises
and commentaries on Aristotle's other writings about the natural
world: *On the Heavens*, *On Generation and Corruption*,
*De anima*, his short treatises on animate powers known as the
'*Parva Naturalia*', and his works on the history,
parts, and generation of animals. Buridan wrote commentaries on nearly
all of these texts. Like his contemporaries, he understood the
speculative sub-disciplines of physics as an orderly progression of
teachings. Thus, demonstration in psychology was thought to borrow its
principles or starting points from physics, the higher science to
which it is subordinated, with its conclusions in turn supplying
principles for demonstrations in the more specialized studies of
sensation and animal locomotion. The ordering metaphor is never far
from Buridan's mind. He remarks to readers of his commentary on
Aristotle's *De motibus animalium* that in this book,
"we descend to the different species of motion in particular,
e.g., to the fact that some animals fly, others swim, and so on"
(DMA I: 535)



Besides logic, Buridan has also enjoyed modern recognition in the
history of natural science or natural philosophy . This is largely due
to the efforts of the pioneering historians of science Pierre Duhem
and Anneliese Maier, who explored Buridan's role in the demise
of the Aristotelian view of the
 cosmos.[49]
 Buridan's major contribution here was to develop and popularize
the theory of impetus, or impressed force, to explain projectile
motion. Rejecting the discredited Aristotelian idea of antiperistasis,
according to which the tendency of a thrown projectile to continue
moving is due to a proximate but external moving cause (i.e. the rush
of air surrounding
 it),[50]
 he argues that only an internal motive force, transmitted from the
mover to the projectile, can properly explain its continued motion.
The theory of impetus probably did not originate with
 Buridan,[51]
 but his account appears to be unique in that he entertains the
possibility that it might not be self-dissipating: "after
leaving the arm of the thrower, the projectile would be moved by an
impetus given to it by the thrower," he says, "and would
continue to be moved as long as the impetus remains stronger than the
resistance, and would be of infinite duration were it not diminished
and corrupted by some contrary force resisting it or by something
inclining it to a contrary motion" (QM XII.9: 73ra). He also
contends that impetus is a variable quality whose force is determined
by the speed and quantity of the matter in the subject, so that the
acceleration of a falling body can be understood in terms of its
gradual accumulation of units of impetus. But despite its
revolutionary implications, Buridan did not use the concept of impetus
to transform the science of mechanics. It is too much to claim, as
Duhem did, that he was a forerunner of Galileo, for he remained
unapologetically Aristotelian in many other respects, continuing to
hold that motion and rest are contrary states of bodies and that the
world is finite in extent. Buridan seems to have been a philosopher
who, though well aware of the shortcomings of the Aristotelian natural
philosophy, tried to reshape as much of it as he could in the face of
a rapidly mechanizing
 worldview.[52]
 His contribution was in transforming certain details. The big,
decisive break was left to his successors.



Buridan's account of motion is in keeping with his approach to
natural science, which is empirical in the sense that it emphasizes
the evidentness of appearances, the reliability of a posteriori modes
of reasoning, and the application of naturalistic tropes or models of
explanation, such as the concept of impetus, to a variety of
phenomena. He is inclined to dismiss purely theological assumptions as
irrelevant to the practice of philosophy, as we see in the following
tongue-in-cheek remark: "one might assume that there are many
more separate substances than there are celestial spheres and
celestial motions, viz., great legions of angels [*magnae legiones
angelorum*], but this cannot be proved by demonstrative arguments
originating from sense perception" (QM II.9:
 73ra).[53]
 But there are some theological considerations that must be taken
seriously. He concedes that divine omnipotence is such that it is
always possible for God to deceive us in ways we could never detect,
although this is tempered by his confidence, for which he cites
empirical evidence, that our ordinary powers of perception and
inductive inference are sufficiently reliable to make "the
comprehension of truth with certitude possible for us" (QM II.1:
9ra). He has little patience for skeptical arguments questioning the
possibility of scientific knowledge, such as those he believed to have
been advanced by Nicholas of Autrecourt, arguing that it is absurd to
demand that all knowledge be demonstrable by reduction to the
principle of non-contradiction. Natural science is about what happens
for the most part, i.e., assuming the common course of nature (Zupko
2003, chs. 12-13). For the same reason, explanatory models in
one special science can be usually applied to others in a way that
enhances our understanding of the phenomena. Thus, the concept of
impetus recurs in Buridan's psychology to explain the difference
between occurrent and dispositional thinking, as well as in his
ethics, to account for the relative ease with which virtuous persons
are able to do the right thing: because they have acquired, or
cultivated within themselves, an impetus to act virtuously.



In psychology, the study of moving beings *qua* animate,
Buridan changed the Aristotelian paradigm in important ways. In
contrast with Thomas Aquinas, who wanted to attribute metaphysically
more robust qualities, such as *per se* subsistence, to the
human soul, Buridan does not think that psychology is in a position to
reveal anything about the inherent nature of its subject, and so he
refuses to speculate about it (Zupko 2007a). He sees the science of
psychology as concerned not with some quidditative concept of the soul
arrived at by *a priori* reasoning, but with specifying the
relation between animate qualities and the soul as their proper
subject: "the natural scientist considers substances only in
relation their motion and operations. Because material forms require
for their operations some matter made appropriate through qualitative
or quantitative dispositions, it is necessary for the natural
philosopher to define forms by means of the matter that is proper to
them. Therefore, the soul certainly has to be defined as a physical,
organic body in the definition provided by natural philosophy"
(QDA II.3, par. 10). This led to an even more attenuated conception of
the soul in the *De anima* commentaries of Buridan's
Parisian successors, Nicole Oresme and Peter of Ailly, for whom the
soul functions as a kind of placeholder whose nature is not even
relevant to psychology (see Zupko 2007b and 2017b). Consideration of
the soul's ultimate nature migrated to the faculty of theology,
where it was considered along with the same Augustinian dreaming
arguments that influenced Descartes (See Zupko 1999 and 2003, chs.
10-11).


## 7. Ethics



Buridan's commentary on Aristotle's *Nicomachean
Ethics* is one of his most influential works, though it is today
perhaps the least studied (Zupko 2013a). It contains significant
discussions of the structure of the will and its relation to the
intellect, the nature of human freedom, the phenomenon of
*akrasia* or weakness of will, practical reason, and the unity
of the
 virtues.[54]



In moral psychology, Buridan appears to effect a compromise between
two rival views on the relation between the will and the intellect:
the intellectualist or naturalist tradition associated with Aristotle
and Thomas Aquinas, according to which the will is always subordinate
to the intellect, and the voluntarist tradition of Augustine and
Franciscan thinkers such as Duns Scotus and William of Ockham, which
held that the will is sometimes capable of acting autonomously.
Buridan's compromise is to argue (with the intellectualists)
that human happiness ultimately consists in an intellectual act,
"the perfect apprehension of God", rather than in a
volitional act such as perfectly willing or perfectly loving God (QNE
X.5: 213rb), although he emphasizes (with the voluntarists) the role
of the will as a self-determining power in achieving that end. The
compromise turns on Buridan's innovative conception of free
choice, which develops Albert the Great's notion that certainty
admits of degrees (see Saarinen 1993, 161-93). The idea is that
even if the will lacks the power to choose evil as such, it is still
able to defer its choice and do nothing if the goodness of one of the
alternatives presented to it is unclear or uncertain. Of course, given
our poor epistemic position in this life, it almost always has this
power because it is almost always possible to doubt the goodness of a
proposed course of action. The compromise is only apparent, however,
because it turns out that the will's act of deferment is
possible only if "the intellect would judge it to be good to
consider the matter further" (QNE III.5:
 44va).[55]
 This claim, together with his assumptions that the will can only
choose non-optimally through ignorance or impediment (QNE
III.3-5; 9), places deferment squarely within the jurisdiction
of the intellect, which must weigh the relative goodness of different
possible courses of action, including deferment. It is not the case
that the will can choose to defer regardless of what the intellect
decides, or that the will can choose to defer even if the intellect
has judged deferment to be less good than some other course of action.
Accordingly, if this is a compromise between the intellectualists and
the voluntarists, it is a disingenuous one. It is more likely that
Buridan simply appropriated voluntarist terminology to express what is
otherwise a straightforwardly intellectualist account of the will,
perhaps to dispel the cloud of heterodoxy which had surrounded
intellectualist moral psychology since the Condemnation of
 1277.[56]



It is also in Buridan's moral psychology that we find the most
plausible explanation of the example which has come down to us known
as 'Buridan's Ass', in which a donkey starves to
death because it has no reason to choose between two equidistant and
equally tempting piles of hay. This particular example is nowhere to
be found in Buridan's writings, although there are versions of
it going back at least to Aristotle (see *De Caelo*
 295b32).[57]
 The best explanation of its association with Buridan is that it
originated as a parody of his account of free choice by later critics,
who found absurd the idea that the will's freedom could consist
in *in*action, i.e., its ability to defer or 'send
back' for further consideration any practical judgment which is
not absolutely certain, leaving the donkey free, but dead.