## 1. Life and Works


### 1.1 Life




Al-Kindi was a member of the Arab tribe of Kinda, which had played an
important role in the early history of Islam. His lineage earned him
the title "philosopher of the Arabs" among later writers.
We know that al-Kindi died after 866 CE, and his death date is usually
put in the early 870s. His birth date is harder to pin down, but he
is said to have served as a scholar under the caliph al-Ma'mun,
whose reign ended in 833, and he was certainly associated with the
court of the next caliph, al-Mu'tasim (reigned
833-842). He is thus usually reckoned to have been born around
800 CE. He was born in Basra and educated in Baghdad. His
philosophical career peaked under al-Mu'tasim, to whom al-Kindi
dedicated his most famous work, *On First Philosophy*, and
whose son Ahmad was tutored by al-Kindi.




Al-Kindi's philosophical activities centered around the
translation movement that had been initiated and supported by the
'Abbasid caliphs since prior to al-Kindi's birth (on this
see Endress 1987/1992, Gutas 1998). Al-Kindi oversaw one of the two
main groups of translators in the ninth century (the other group was
led by Hunayn ibn Ishaq). The "Kindi circle" (see Endress
1997) translated numerous works of philosophy and science from Greek
into Arabic. (On the output of the circle see below, 2.1.) Al-Kindi
seems to have been a mediator between the patrons of these translators
and the scholars who actually did the translating, many of whom were
Syrian Christians or of Syrian extraction. His own writings might be
thought of as a sustained public relations campaign intended to display
and advertise the value of Greek thought for a contemporary ninth
century Muslim audience.


### 1.2 Works




We are fortunate in having a list of titles of works ascribed to
al-Kindi, which is found in the *Fihrist* of the tenth century
bookseller Ibn al-Nadim. Thanks to Ibn al-Nadim we know that al-Kindi
wrote hundreds of treatises on a very wide variety of scientific and
philosophical disciplines. Indeed the scientific and mathematical
titles far outnumber the philosophical titles. Many of the latter would
now be lost if not for a single manuscript, held in Istanbul, which
contains most of al-Kindi's extant philosophical writings (edited
in Abu Rida 1950 and 1953; several important texts are edited and
translated in Rashed and Jolivet 1998). This includes the work for
which he is best known, *On First Philosophy*. Our version of
this treatise is incomplete, comprising only the first part, which is
divided into four sections. The first section is essentially an
exhortation to the reader to honor Greek philosophical wisdom. The
second contains al-Kindi's celebrated discussion of the eternity
of the world. The third and fourth establish the existence of a
"true One," i.e. God, which is the source of unity in all
other things, and consider the inapplicability of language to this true
One.




The Istanbul manuscript also includes one of the few copies of
al-Kindi's *On the Intellect* to survive in Arabic (it is
also preserved in Latin translation). This is the first treatise in the
Arabic tradition to give a taxonomy of the types of intellect, such as
will become familiar in al-Farabi, Avicenna and Averroes. Other works
shed further light on al-Kindi's psychology (i.e. theory of
soul): the *Discourse on the Soul* consists of supposed
quotations from Greek philosophers, *That There are Separate
Substances* uses Aristotle's *Categories* to prove
that the soul is immaterial, and *On Sleep and Dream* gives an
account of prophetic dreams in terms of Aristotle's theory of the
imagination. Related to al-Kindi's psychological theories is his
only significant surviving work on ethics, *On Dispelling
Sorrows*. (He also composed a collection of ethical anecdotes and
sayings ascribed to Socrates, for which see Fakhry 1963.)




Al-Kindi sets out his cosmological theories in two further texts
found in the same manuscript, *On the Proximate Agent Cause of
Generation and Corruption* and *On the Prostration of the
Outermost Sphere*. Also relevant here are numerous works on
meteorology and weather forecasting. These apply the same cosmological
ideas to show how heavenly motion produces rain and other
meteorological phenomena in the lower world where we live. While these
works are influenced by Aristotle, al-Kindi also draws on other Greek
sources, such as Ptolemy. His knowledge of the Greek scientific
tradition was in fact extensive. For instance, he uses Euclid and ideas
that can be traced to Ptolemy in a well-known work on optics, *On
Perspectives*, which is preserved only in Latin. Al-Kindi's
extant scientific corpus is sizable and includes treatises on the
manufacture of drugs, music, astrology, and mathematics (see further
Rosenthal 1942). But the focus here will be on al-Kindi's
philosophical views.


## 2. Influences on al-Kindi


### 2.1 Greek influences




As one would expect given his prominent role in the translation
movement, al-Kindi's works are suffused with ideas from Greek
thought. His philosophical works are indebted in part to the
mathematical and scientific authors translated by his day, for
instance Nicomachus of Gerasa; Euclid influenced his methodology as
well as his mathematics (cf. Gutas 2004). But the most important
influence on his philosophy was from Aristotle, whose corpus al-Kindi
surveys in a treatise called *On the Quantity of Aristotle's
Books* (Abu Rida 1950, 363-84; also Guidi and Walzer 1940,
Cortabarria Beitia 1972, Jolivet 2004, Ighbariah 2012). This work provides a fairly
thorough overview of Aristotle's corpus, though al-Kindi clearly has
not read some of the treatises he discusses. When al-Kindi comes to
mention the contents of the *Metaphysics* he gives the
following, rather surprising, summary:



> 
> 
> His purpose in his book called *Metaphysics* is to explain
> things that subsist without matter and, though they may exist together
> with what does have matter, are neither connected nor united to matter;
> to affirm the oneness of God, the great and exalted, to explain His
> beautiful names, and that He is the agent cause of the universe, which
> perfects [all things], the God of the universe who governs through His
> perfect providence and complete wisdom.




While this may not look like an accurate description of Aristotle's
*Metaphysics*, it is a wholly accurate description of
al-Kindi's own conception of the science of metaphysics. That he
conflates metaphysics with theology is clear from the opening of
*On First Philosophy*, which says that since philosophy in
general is the study of truth, "first philosophy" is
"the knowledge of the first truth who is the cause of all
truth." And indeed Aristotle's *Metaphysics* is a major
influence on this work. However, as is typical of al-Kindi's
philosophical writings, *On First Philosophy* also makes
extensive use of ideas from translations of Neoplatonic writings. The
proof for the existence of a "true One" is based in part
on Proclus (as shown in Jolivet 1979), and one can detect influences
from the Arabic version of Plotinus produced in al-Kindi's circle, the
so-called *Theology of Aristotle*. Perhaps the most important
single influence, however, is an attack on Aristotle by the
Neoplatonist Christian thinker John Philoponus, over the issue of the
world's eternity.



*On First Philosophy*, then, is a particularly good example of
how al-Kindi combines Neoplatonic and Aristotelian ideas in his vision
of a coherent philosophy derived from the Greeks. The way for this
synoptic conception of the Greek inheritance had actually been prepared
by the Neoplatonists themselves, whose commentaries on Aristotle
presage the harmonizing tendencies obvious in al-Kindi. But as a
promoter of Greek wisdom, al-Kindi would in any case have been eager to
deemphasize any tensions between Greek philosophers, or any failings on
the part of Greek thinkers. For example he gives no sign that his
position on the eternity of the world departs from that of Aristotle.
(Interestingly he is more willing to recognize shortcomings on the part
of Greek scientific thinkers, for instance in Euclid's optics,
though even here he emphasizes the need for a charitable approach.)
Later in the first section of *On First Philosophy*, al-Kindi
unleashes a torrent of abuse against unnamed contemporaries who
criticize the use of Greek ideas:



> 
> 
> We must not be ashamed to admire the truth or to acquire it, from
> wherever it comes. Even if it should come from far-flung nations and
> foreign peoples, there is for the student of truth nothing more
> important than the truth, nor is the truth demeaned or diminished by
> the one who states or conveys it; no one is demeaned by the truth,
> rather all are ennobled by it.




Although al-Kindi was unyielding in his support for the ideas
disseminated in the translation project, he was inevitably influenced
by the intellectual currents of his day. This comes out most clearly
when al-Kindi uses Greek ideas to engage with the problems of his time,
especially in the arena of theology.


### 2.2 Contemporary influences




Two examples of this engagement, to be discussed in more detail in
the next section, are al-Kindi's treatment of divine attributes,
and his views on creation. As we will see al-Kindi held an austere view
on the question of attributes, on the basis that predication invariably
implies multiplicity, whereas God is unrestrictedly one. This has been
compared (Ivry 1974, Adamson 2003) to the position of the
Mu'tazilites, who were the main contemporary theologians of the
ninth century. Mu'tazilite influence may also be present in
al-Kindi's theory that creation is a "bringing to be of
being from non-being," and especially in his denial that creation
can be eternal. (This may be related to the Mu'tazilite claim
that the Koran is created and not eternal; see Adamson 2007, ch.4.)




Al-Kindi uses philosophy to defend and explicate Islam in several
works. He wrote a short treatise attacking the Christian doctrine of
the Trinity, using concepts drawn from the *Isagoge* of Porphyry
(al-Kindi's refutation was the subject of a counter-refutation by
the tenth century Christian philosopher, Yahya ibn 'Adi; see
Perier 1920). While this is the only extant work that engages in
theological controversy, we know from the *Fihrist* that he
wrote other treatises on similar themes. The extant corpus also
contains passages in which al-Kindi expounds the meaning of passages
from the Koran. Most striking, perhaps, is his discussion of creation
*ex nihilo* in the midst of *On the Quantity of
Aristotle's Books*. This passage is a commentary on Koran
36: 79-82. Al-Kindi mentions the same Koranic passage, and discusses the
special nature of prophetic knowledge, in a meteorological work
entitled *On Why the Higher Atmosphere is Cold* (see Abu Rida
1953, 92-93). The cosmological work *On the Prostration of the
Outermost Sphere*, meanwhile, is entirely devoted to explaining the
Koranic verse "the stars and the trees prostrate
themselves" (55: 6) in terms of al-Kindi's account of
heavenly influence on the sublunary world. Al-Kindi's remarks
here show his interest in the contemporary disciplines of grammar and
Koranic exegesis.




A desire to integrate Greek ideas into his own culture is shown in a
different way by *On Definitions*, a list of technical
philosophical terms with definitions (see Abu Rida 1950, 165-79;
also Allard 1972, Klein-Franke 1982). This work is ascribed to
al-Kindi, and though its authenticity has been doubted it is almost
certainly at least a production of al-Kindi's circle. Most of the
defined terms correspond to Greek technical terms, and thus build up
an Arabic philosophical terminology which is intended to be equivalent
to that of the Greeks. It is striking that, so early in the Arabic
philosophical tradition, there was already a perceived need for a
novel technical language for communicating philosophical ideas in a
different setting (and of course for translating Greek into
Arabic). Some, though certainly not all, of the terms listed in *On
Definitions* will indeed become standard in the later
philosophical tradition.


## 3. Metaphysics


### 3.1 Divine simplicity




Al-Kindi's most significant work, *On First Philosophy*
(for which see Abu Rida 1950, 97-162, Ivry 1974, Rashed and Jolivet
1998, 9-99), is devoted to "first philosophy" or
metaphysics, a science al-Kindi immediately identifies with the study
of God. Since all philosophy is an inquiry into truth, first philosophy
is the knowledge of God, who is "the first truth and the cause of
all truth." While this may not sound like it has much to do with
Aristotle's understanding of first philosophy as the science of
being, al-Kindi closely associates being with truth ("everything
that has being has truth"). For him, to say that God is the cause
of all truth is tantamount to saying that God is the cause of all
being, a point made more explicit at the end of what remains to us of
*On First Philosophy* (see further below, 3.2).




The central concept in the theology of *On First Philosophy*,
however, is neither truth nor being, but oneness. Indeed al-Kindi
argues for a first cause of being precisely by arguing for a first
cause of oneness, and asserting that "bringing something to
be" means imposing unity of a certain kind. Al-Kindi's
philosophical theology thus has two main aspects: a proof that there
must be some "true One" that is the cause of the unity in
all things, and a discussion of the nature of this true One. These
aspects are treated, respectively, in the third and fourth sections
of *On First Philosophy*.




In the third section, al-Kindi first proves that nothing can be its
own cause, a point that is not used explicitly in what follows, but
may be intended to show that nothing can be the cause of its own
unity. He then undertakes an exhaustive survey of the various types of
"utterance (*lafz*)." Following Porphyry's
*Isagoge*, he classifies all predicates or terms
(*maqulat*) into genus, species, difference, individual, proper
accident, and common accident. Taking them in turn, al-Kindi argues
that each type of predicate implies both unity and multiplicity. For
example, *animal* is one genus, but it is made up of a
multiplicity of species; *human* is one species but is made up
of many individuals; and a single human is one individual but made up
of many bodily parts. Finally, al-Kindi seeks an explanation for the
association of unity and multiplicity in all these things. He argues
that the association cannot be merely the product of chance; nor can
it be caused by any part of the set of things that are both one and
many. So there must be some external cause for the association of
unity and multiplicity. This cause will be exclusively one, entirely
free of multiplicity: al-Kindi expresses this by saying that it is
"essentially" one, whereas the other things are
"accidentally" one. He also speaks of it as "one in
truth," whereas other things are one
"metaphorically." In short, the cause in question is the
"true One," or God.




Now, since we have already seen that every sort of term or
expression implies multiplicity as well as unity, it is no surprise
that in section four of *One First Philosophy* al-Kindi goes on
to argue that the various sorts of predicate are inapplicable to the
true One. He sums up his conclusion as follows (Rashed and Jolivet
1998, 95):



> 
> 
> Thus the true One possesses no matter, form, quantity, quality, or
> relation. And is not described by any of the other terms: it has no
> genus, no specific difference, no individual, no proper accident, and
> no common accident. It does not move, and is not described through
> anything that is denied to be one in truth. It is therefore only pure
> unity, I mean nothing other than unity. And every unity other than it
> is multiple.




As mentioned above, this conclusion has been compared to the view of
those contemporary theologians referred to as Mu'tazilites. They
similarly took a strict view on the question of divine attributes,
arguing that God's simplicity ruled out the acceptance of any
attributes distinct from God's essence. However it is Greek
antecedents that are clearly the main influence on al-Kindi here. His
"true One" bears a strong resemblance to the first
principle of the Neoplatonists. Indeed we might be reminded of Plato
himself, insofar as al-Kindi's God seems to function like a
Platonic Form. Just as the Form of Equal is entirely equal and not at
all unequal, and serves to explain equality in other things, so God is
entirely one, not at all multiple, and explains the unity in other
things.


### 3.2 Creation




This is, however, only a part of al-Kindi's view on divine
causation. Because, as we have seen, al-Kindi thinks that to be a thing
of a certain kind is to be one in a certain way, he infers that the
true One is the cause of being as well as unity (see further Adamson
2002b). In particular, he believes that God is an "agent"
or efficient cause. This view is expressed in a succinct text (possibly
a fragment from a longer, lost work) headed with the title *On the
True, First, Complete Agent and the Deficient Agent that is
Metaphorically* [*an Agent*] (Abu Rida 1950, 182-4). The
text begins as follows:



> 
> 
> We say that the true, first act is the bringing-to-be of beings from
> non-being. It is clear that this act is proper to God, the exalted, who
> is the end of every cause. For the bringing-to-be of beings from
> non-being belongs to no other. And this act is a proper characteristic
> [called] by the name "origination."




Al-Kindi goes on to explain that whereas God is a "true"
agent, since He is a cause of being and acts without being acted upon,
all other agents are only "metaphorically" agents, because
they both act and are acted upon. The force of the term
"metaphorical" here is the same as it was in *On First
Philosophy*: just as created things are both many and one, and thus
not "truly" one, so they are both passive and active, and
thus not "truly" agents.




This short text raises two interesting questions about how al-Kindi
conceived of divine action. First, what does he have in mind when he
describes God's agency as being mediated by the action of
"metaphorical agents" (God "is the proximate cause
for the first effect, and a cause through an intermediary for His
effects that are after the first effect")? Second, what is
involved in "bringing being to be from non-being"?




Regarding the first question, one might suppose that al-Kindi is
following Neoplatonic texts, and that he has in mind a mediated
emanation of effects from the first principle. If this is right, then
the "first effect" will be the "world of the
intellect" mentioned in other Kindian texts (e.g. the
*Discourse on the Soul*, repeating this phrase from the
*Theology of Aristotle*). This is supported by a non-committal
remark in *On First Philosophy* that "one might think the
intellect is the first multiple" (Rashed and Jolivet 1998, 87).
But it seems at least as likely that the "first effect"
mentioned here is the world of the heavens: by creating the heavens and
setting them in motion, God indirectly brings about things in the
sublunary world (see further below, 5.2). This would be a more
Aristotelian version of the idea that divine causation is mediated.




Regarding the second question, the idea that God is an *agent*
*cause of being* may likewise seem at first to be a departure
from Aristotle. But in fact Neoplatonist authors like Ammonius had
explicitly argued that Aristotle's God was an efficient cause of
being, not just a final cause of motion. And a passage in *On the
Quantity of Aristotle's Books* -- the aforementioned
discussion of Koran 36: 79-82 -- understands creation on the
model of Aristotelian change, in which something passes from one
contrary to another. In the case of creation, one contrary is
"non-being" and the other "being." Al-Kindi's
discussion of this has parallels in ninth century theological
discussions of creation (see Adamson 2003). But his main source,
surprisingly, is Ammonius' student John Philoponus, a Christian
Neoplatonist who had also spoken of creation as bringing something to
be "from non-being." What separates al-Kindi and
Philoponus from Aristotle is their idea that this kind of
"change" from non-being to being requires no subject. For
example, for there to be a change from non-white to white, there must
be some subject or substrate for both the privation of the whiteness
and the whiteness itself (for instance the fence that goes from being
non-white to being white when it is painted). God, by contrast, can
bring about being *ex nihilo*, with no subject for the change.
Al-Kindi emphasizes also that God's creative act requires no time to
be realized.


### 3.3 Eternity of the world




These two points bring us to a more extensive use of Philoponus by
al-Kindi, in the latter's well-known argument that the world is
not eternal (for which see Davidson 1969 and 1987, and Staley 1987).
Most Greek philosophers followed Aristotle in holding that the world is
eternal, meaning not only that it will never cease to exist, but that
it has always existed. This was the doctrine of Aristotle and the
Stoics, and also of orthodox Neoplatonists, who interpreted
Plato's *Timaeus* as likewise committed to the past
eternity of the world. Philoponus was an exception to this rule. In a
work rebutting the Neoplatonist Proclus' arguments in favor of
the world's eternity, he argued at great length that
Plato's *Timaeus* rightly envisions a world with a
beginning in time. And in another work directed against Aristotle,
Philoponus tried to undermine the arguments of the *De Caelo*
and *Physics* by which Aristotle had shown that the world is
eternal.




In section two of *On First Philosophy*, and several other
short works that repeat the same arguments found in this section,
al-Kindi follows arguments that derive from Philoponus. (Exactly which
text or texts by Philoponus he used is unclear, but it would seem that
he at least knew parts of *Against Aristotle*.) Interestingly,
al-Kindi completely ignores a major aspect of Philoponus'
polemic: in the *De Caelo*, Aristotle had argued that the
heavens must be eternal, because they have perfect, circular motion and
are therefore not made out of any of the corruptible four elements of
our lower world. Whereas Philoponus attacks this cosmology with a
lengthy and detailed refutation, al-Kindi simply accepts that the
heavens are made out of an ungenerable and indestructible fifth element
- but blithely adds that they are nonetheless originally brought
into being by God with a beginning in time. (For this see the treatise
*That the Nature of the Celestial Sphere is Different from the
Natures of the Four Elements*, edited at Abu Rida 1953, 40-6.)




When al-Kindi comes to argue explicitly against the eternity of the
world, he uses Philoponus' strategy of using Aristotle against
himself. Aristotle famously held that there can be no such thing as an
actual infinite. Thus, for instance, the body of the world cannot be
infinitely large. Because the cosmos is finite in spatial magnitude,
argues al-Kindi, nothing predicated of the body of the cosmos can be
infinite. Since time is one of the things predicated of this body, time
must be finite; therefore the world is not eternal.




This argument seems to be a poor one. Even if Aristotle admits that
nothing infinite can be predicated of a finite body, he will want to
say that al-Kindi's argument fails to take full account of the
distinction between *actual* and merely *potential*
infinities. An actual infinity is an infinity which is simultaneously
present in its entirety - for example, an infinitely large body,
or in general any set with an infinite number of members existing at
the same time. A potential infinity is when a finite magnitude can be
extended or multiplied indefinitely. For example, Aristotle thinks
that any finite magnitude of space or time is potentially infinite, in
that it can in principle be divided into as many parts as one wishes,
with smaller divisions still possible. The body of the cosmos, as
al-Kindi admits himself, is also potentially infinite, in the sense
that there is nothing conceptually impossible about increasing its
size indefinitely. Notice, though, that in either case the actual
result of such a process will be finite: any determinate addition to
the size of a body will still yield a body of finite size. Likewise,
no matter how finely I divide a body, any particular act of division
will yield a finite number of parts.




Now, Aristotle believes that the eternity of the world commits him
only to a *potential* infinity. This is because saying that the
world has always existed does not imply that any infinity is
*presently* actual. Rather, it implies only that "the
world has already existed for *N* years" will be true for
any value of N. One can, so to speak, go as far as one wishes into the
past, positing increasingly large (but still finite) periods of past
time, just as one can divide a body as finely as one wishes. And it is
far from clear that this sort of *potential* infinity is
inapplicable to a finite magnitude. Does al-Kindi have any response to
this?




He does, though his response comes only at the end of his treatment
of the world's eternity. The response, found also in Philoponus,
is that even to reach the present moment, an actually infinite number
of moments must already have elapsed. In other words, there is
currently an actually infinite number of moments (or years, or
whatever) that have elapsed "since the world began." And,
as Aristotle himself says, the infinite cannot be traversed. Whether
this argument is successful is unclear. It seems to presuppose that we
select an infinitely distant point in past time, and then reckon the
number of years that have elapsed since then. But Aristotle will
presumably want to block the initial move of selecting an infinitely
distant point in past time, insisting that any *particular*
point we choose in the past will be removed from the present by a
merely finite number of years.


## 4. Psychology


### 4.1 The human soul




We have two works by al-Kindi devoted to the ontology of the human
soul: *That There are Incorporeal Substances* and *Discourse
on the Soul*. The two depend on very different Greek sources, and
are very different in rhetorical presentation. But the doctrine that
emerges from them is not necessarily inconsistent.



*That There are Incorporeal Substances* (Abu Rida 1950,
265-69, Adamson and Pormann 2009) is a creative application of
ideas from Aristotle's
*Categories* to the problem of showing that the human soul is
an immaterial substance. Al-Kindi takes up this task in stages, first
proving that the soul is a substance, then showing that it is
immaterial. He argues that the soul is a substance by drawing on the
opening chapters of the *Categories* to claim that the essence
of something shares a name and definition with that thing. Since the
soul is the essence of the living being, and the living being is a
substance, the soul is also a substance. Furthermore, it is an
immaterial substance: for the soul is "the intellectual form of
the living thing," and an intellectual form is a species. But
species, al-Kindi argues, are immaterial; therefore the soul is
immaterial. Among the problematic moves in this train of argument is
the identification of the human soul with the species of human. This
would seem to be al-Kindi's attempt to bring together the idea of
species, which is a "secondary substance" in the
*Categories*, with the doctrine of form found in such works as
the *De Anima* and *Metaphysics*. Al-Kindi simply
conflates the two, without argument - he does not address the
obvious question of how there can be many human souls, all of which
are identical with the single species *human*.




Apart from brief opening and closing remarks, *Discourse on the
Soul* (Abu Rida 1950, 272-80; also D'Ancona 1996,
Genequand 1987, Jolivet 1996) consists entirely of supposed quotes
from Greek authorities - Plato, Pythagoras, and Aristotle
- about the nature of the soul. The actual sources used are
unclear, though the *Republic* is the ultimate source for a
section describing Plato's tripartite soul. The section on Aristotle
is a fable about a Greek king, and has nothing to do with any extant
Aristotelian work. The tenor of these remarks is hortatory, ascetic
and even visionary: our task is to cleanse our souls from the
"stains" that adhere to it from the body, and to ascend
through the heavenly spheres, ultimately to the "world of the
intellect" where it will reside in "the light of the
Creator." The soul in question here would seem to be the
rational soul: the lower parts of Plato's tripartite soul (the
irascible and concupiscent parts) are described as faculties seated in
the body. The point of this psychological doxography is not unlike
that of *Incorporeal Substances*: the soul is a "simple
substance," separate from body. Indeed this is presented as the
overall message of the treatise in al-Kindi's closing remarks.


### 4.2 Epistemology




This rigorously dualist psychology has far-reaching effects in
al-Kindi's epistemology and ethics. It is clear from the
*Discourse* that when al-Kindi speaks of the soul as separate
from body, even during our worldly life, he is referring only to the
intellective or rational soul. While this does not by itself rule out
that intellection and reason are somehow grounded in bodily experience,
al-Kindi does not pursue an empiricist program in contexts where he
addresses epistemological issues.




The most important text on epistemology is al-Kindi's
best-known work apart from *On First Philosophy*, namely *On
the Intellect* (Abu Rida 1950, 353-8; also McCarthy 1964,
Ruffinengo 1997). This treatise has received an unusual amount of
attention, despite its brevity and compressed argument, because it is
the first Arabic work to show the influence of Greek taxonomies of the
intellect into levels or types. (See especially Jolivet 1971, with
Endress 1980.) These taxonomies, with various versions put forward by
Alexander, Themistius, Philoponus and other commentators, were in turn
attempts to systematize Aristotle's remarks on intellect in
*De Anima* book 3 and elsewhere.




Far from grounding intellect in sensation, al-Kindi argues in *On
the Intellect* that the human intellect has a parallel, but
separate, function to human sense-perception. (For a similar contrast
see also *On First Philosophy*, section 2.) Just like sensation,
the human intellect in itself begins in a state of potentiality. This
is the first type of intellect, the potential intellect, which is
merely an ability to grasp intellectual forms. Once it grasps a form
and is actually thinking, it becomes "actual intellect." We
are then able to think about these forms at will. Our ability to do so
is what al-Kindi calls the "acquired intellect" (not to be
confused with "acquired intellect" in al-Farabi, who means
by this a comprehensive attainment of the many intellectual forms).
Notice that these types of intellect are really only the same, human
intellect in three different states: wholly potential, wholly actual,
and temporarily potential but able to actualize at will.




But how in the first place do we get from potential intellect to
actual intellection? It is here that al-Kindi might have told some sort
of empiricist story, perhaps involving abstraction; such a story plays
at least some role in al-Kindi's successors al-Farabi and
Avicenna. But instead al-Kindi gives a thoroughly intellectualist
account of how we come to think, one which is parallel to, but distinct
from, his account of sensation. Just as sensation is actualized by an
external sensible form, so intellect is actualized by an external
intelligible form. This form will reside in the final type of
intellect, the "first intellect," which is al-Kindi's
version of the infamous "maker intellect" in
Aristotle's *De Anima* 3.5. While it is unclear what
position this first intellect is meant to have in al-Kindi's
ontology, it is clear that it is distinct from human intellect. The
first intellect is "always in act," which means that it can
serve as an external source for intelligible forms, just as sensible
object serves as an external source for a sensible form.




We get some sense of how al-Kindi might have applied this highly
intellectualist epistemology in specific contexts from works on
recollection and on dreams. His *On Recollection* (for which see
Endress 1986 and 1994) argues explicitly that we *cannot* derive
intelligible forms from sense-perception. Thus we do not
"learn" these forms, but simply "remember" them
from before the soul entered into the body. Here al-Kindi is of course
broadly following the account of recollection given by Plato in the
*Meno* or *Phaedo*, though how he might have known of
this account remains obscure. (Most likely it is from an Arabic
version, perhaps in summary, of the *Phaedo*.)




A longer and more detailed text is *On Sleep and Dream* (Abu
Rida 1950, 293-311; also Ruffinengo 1997), which gives a naturalistic
account of why prophetic dreams occur, and how they may be interpreted.
Here al-Kindi's chief source was Aristotle's *Parva
Naturalia*, which include the works *On Sleep*, *On
Dreams*, and *On Prophecy in Sleep*. The extant Arabic
version of these texts, which may well be related to the version used
by al-Kindi, is importantly different from the Greek version, in that
it admits that genuinely prophetic dreams can be sent from God (cf.
Pines 1974). If al-Kindi knew this version then he follows it only in
part: he embraces the idea of prophetic dreams, but does not claim that
they come to us from God. To explain dreams al-Kindi invokes a faculty
we have not yet discussed, namely imagination or *phantasia*.
Following Aristotle, al-Kindi says that dreams occur when we are
sleeping because the senses are no longer active, and the imagination
has free rein to conjure up forms on its own. We are also given a
physiological account of sleep, which departs from Aristotle by placing
the imaginative faculty in the brain. Whereas Aristotle has some
difficulty explaining, and is in fact rather skeptical about, the
phenomenon of prophetic dreams, al-Kindi is enthusiastic about them. He
even explains the various types of dream, with their accuracy
determined by the physical state of the brain. But despite the
physiological aspects of al-Kindi's account, the fundamental
explanatory work is done by the incorporeal soul, which
"announces" its visions of the future to the imagination.
Again, the rational soul grasps its objects by itself. Tellingly,
al-Kindi thinks that sensation hinders this power of the soul, rather
than contributing anything to it.


### 4.3 Application to ethics




Given that al-Kindi sharply divides the rational soul from the body
and the lower psychological faculties, and that he sees the rational
soul as our true "self" or "essence" and as the
only part of us that survives the death of the body, it is no surprise
that his ethical thought is likewise highly intellectualist.
Unfortunately, the numerous works on ethical and political topics
ascribed to him in the *Fihrist* are almost all lost. The most
significant remaining text is *On Dispelling Sadness* (Ritter
and Walzer 1938, also Butterworth 1992, Druart 1993, Jayyusi-Lehn 2002,
Mestiri and Dye 2004). This is also the work of al-Kindi that will be
most often cited by subsequent thinkers, for example by Miskawayh in
his *Tahdhib al-Akhlaq* (*The Refinement of
Character*).



*On Dispelling Sadness*, as its title indicates, is a work in
the genre of philosophical consolation. Much of the text consists in
practical advice, maxims and anecdotes that one may bear in mind when
one finds oneself affected by sorrow. One particularly striking passage
allegorizes our earthly life as a temporary landfall during a sea
voyage; this image derives ultimately from Epictetus. The philosophical
foundations of the treatise, though, are laid in the early sections,
where al-Kindi gives a principled argument against placing value on
physical objects. By their very nature, he says, wealth and other
physical goods are vulnerable and transitory. No one can be sure that
their possessions will not be taken from them - they may
"be seized by any power." And more crucially, the very fact
that they are physical means that they are subject to generation and
corruption, and are therefore fleeting. Instead, we should value and
pursue things that are stable and enduring, and that cannot be taken
from us: these will be the things in the now familiar "world of
the intellect." To the extent that one's desires are
directed solely towards intelligible things, one will be invulnerable
to sadness. This argument, then, shows that sadness is always needless.
The anecdotes and more practical "remedies" offered in the
rest of the treatise are intended to make it easier for us to accept
and live in accordance with this conclusion.


## 5. Science


### 5.1 The use of mathematics




Despite the anti-empiricist character of al-Kindi's epistemology noted
above, he devoted enormous energy to various branches of the physical
sciences. Particularly well represented in the extant corpus are his
work on optics and medicine, especially the compounding of drugs (for
optics see Rashed 1997; for medicine see Gauthier 1939, Klein-Franke
1975, Celentano 1979; for these aspects of al-Kindi's thought
generally see Adamson 2007, ch.7). What is characteristic about
al-Kindi's approach to such topics is the use of mathematics. It has
been persuasively argued that mathematics was fundamental to
al-Kindi's own philosophical method (Gutas 2004, cf. Endress 2003); a
good example is his mathematical approach to Aristotle's categories,
which makes quantity and quality fundamental for Aristotelian logic
(Ighbariah 2012). Certainly he missed no opportunity to apply
mathematical techniques to what we would now think of as
"scientific" topics. In addition, he wrote numerous works
on music (edited in Zakariyya' 1962), which for the ancients and
al-Kindi himself was a branch of the mathematical sciences. He also
wrote extensively on more recognizably mathematical topics, as is
attested by the *Fihrist*, though again much of this material
is lost.




A good example of how al-Kindi applied mathematics to other fields
is his use of geometry in optics (see further Lindberg 1971, Rashed
1997, Adamson 2006). On this subject al-Kindi followed the tradition
inaugurated by Euclid, and carried on by Ptolemy and others, in which
geometrical constructions were used to explain phenomena such as visual
perspective, shadows, refraction, reflection, and burning mirrors. This
procedure implies that light and vision can be formalized as
geometrical lines, an implication that al-Kindi and his sources embrace
by claiming that vision occurs when "rays" emitted from the
eyes along straight lines strike a visual object. Likewise, objects are
illuminated when a light source emits light rays that strike the
objects' surfaces. Aspects of al-Kindi's account anticipate
that of Ibn al-Haytham, who some decades later would be the first to
explain vision accurately.




Now, this account based on "rays" also seems to underlie
al-Kindi's most ambitious work on the physical sciences: a
lengthy treatise entitled *On Rays* (*de Radiis*, for
which see D'Alverny and Hudry 1974) and preserved only in Latin.
There is some question as to its authenticity, but it seems plausible
that *On Rays* represents al-Kindi's attempt to explain
all physical interaction - from heating and cooling, to vision,
to astral influence, to magical incantations - in terms of a
fundamentally geometrical mechanism. (For connections to the optical
works, see Travaglia 1999.)


### 5.2 Cosmology




A central part of *On Rays* explains that the stars and
planets bring about events in the sublunary world by means of rays
emitted from the heavenly bodies to points on the earth's
surface. This differs from an account found in several other
cosmological treatises by al-Kindi, where he follows Alexander of
Aphrodisias in holding that the heavenly bodies literally heat up the
lower world by means of friction as they pass over it. In either case,
however, the account given is intended to explain the efficacy of the
science of astrology. Al-Kindi wrote numerous works on this subject,
and his associate Abu Ma'shar was the greatest figure in Arabic
astrology. Both of them saw astrology as a rational science,
undergirded by a well-worked out theory of physical causes (see further
Burnett 1993, Adamson 2002a).




Al-Kindi's corpus includes several treatises on cosmology,
explaining and defending a picture of the cosmos as four concentric
circles of elements, which are mixed together by the outer, heavenly
spheres to yield complex compound substances like minerals, plants, and
animals. Though al-Kindi's main influences are works of Aristotle
and his commentators, especially Alexander, he also knows something of
the *Timaeus*, as is shown by a treatise explaining why Plato
associated the elements and heavens with the Platonic solids (Abu Rida
1953, 54-63; also Rescher 1968).




One respect in which al-Kindi follows Alexander is his conviction that
the heavenly spheres are the means by which God exercises providence
over the sublunary world (see Fazzo and Wiesner 1993). Al-Kindi's
bold claims for astrology already commit him to the idea that a wide
range of specific events can be predicted on the basis of astral
causation. His doctrine of providence goes further by implying that
*all* events in the lower world are caused by the stars,
which are carrying out the benign "command" of God. This
doctrine is set out in *On the Prostration of the Outermost
Sphere* (Abu Rida 1950, 244-261, Rashed and Jolivet 1998, 177-99)
and *On the Proximate Agent Cause of Generation and Corruption*
(Abu Rida 1950, 214-237). The former explains that the heavens are
possessed of souls, and freely follow God's command so as to move in
such a way that the providentially intended sublunary things and
events will come about. This, according to al-Kindi, is what the Koran
refers to when it says that the stars "prostrate"
themselves before God. In *Proximate Agent Cause*, meanwhile,
al-Kindi gives a more detailed account of the means by which the
heavens cause things in the lower world (here he invokes friction, not
rays). The most obvious effect of the stars on our world is of course
the seasons, because the sun (due to its size and proximity) is the
heavenly body with the most powerful effect. If there were no such
heavenly causation, according to al-Kindi, the elements would never
have combined at all, and the lower realm would consist of four
spheres of unmixed earth, water, air and fire.




Al-Kindi's account of astral causation and providence is a very good
example of his philosophical method: combining and building on ideas
taken from Aristotle, later Greek philosophers, and
"scientific" authors like Ptolemy, he gives a rational
account of a central concept in Islam. *Prostration* shows that
he is even willing to use such an account to expound the Koran itself.
Al-Kindi is confident that, once exposed to judicious presentations of
Greek wisdom, his more enlightened contemporaries and sponsors will
agree that these foreign texts can be used -- jointly with
autochthonous "Arabic" disciplines like grammar -- in
the service of a deeper understanding of Islam itself.


## 6. Legacy




Al-Kindi's optimism on this score was not necessarily borne
out in subsequent generations. But among thinkers influenced by
al-Kindi, one can discern a continuing tendency to harmonize
"foreign" philosophy with the "indigenous"
developments of Muslim culture. This is one feature of what might be
called the "Kindian tradition," an intellectual current
that runs up through the tenth century, which is most obviously
represented by first and second generation students of
al-Kindi's. Particularly prominent among these figures is
al-'Amiri, a well-known Neoplatonist thinker who was a second
generation student of al-Kindi's (the link was al-Kindi's
student Abu Zayd al-Balkhi). Also influenced by al-Kindi were the
Jewish thinker Isaac Israeli (on whom see Altmann and Stern 1958) and
the aforementioned tenth century polymath Miskawayh.




While al-Kindi is only rarely cited by authors writing in Arabic
later than the tenth century, he was a significant figure for Latin
medieval authors. Most influential were his works on astrology (see
Burnett 1999); but works like *On the Intellect* were also
translated, and as noted above there are works in the Kindian corpus
that are extant only in Latin. One of these, *On Rays*, was the
target of a polemic composed by Giles of Rome.




To this we might add that philosophy in the Islamic world was itself
a broader legacy of al-Kindi's, and this in two respects.
Firstly, the translations produced in the Kindi circle would become
standard philosophical texts for centuries to come - particularly
influential would be their translations of certain Aristotelian works
(such as the *Metaphysics*) and of Plotinus, in the *Theology
of Aristotle*. Secondly, though authors like al-Farabi and Averroes
hardly mention al-Kindi by name (al-Farabi never does so, and Averroes
does so only to criticize his pharmacological theory), they are
carrying on his philhellenic project, in which the practice of
philosophy is defined by an engagement with Greek philosophical
works.