Medieval Philosophy – Prof. Dr. Robert C. Koons

http://www.utexas.edu/cola/depts/philosophy/faculty/koons/phl349/syllabus.htm

Lecture # 22: Theory of Knowledge: ibn Sina, ibn Rushd, Aquinas

I. Ibn Sina

On epistemology, Ibn Sina argued that the human mind can receive and catalog sense impressions and can
make the judgments necessary for practical action. However, the highest act of the intellect –- that of
abstracting universals from sense impressions of corresponding particulars –- is beyond the capacity of the
finite, embodied human mind. Instead, following a cryptic remark by Aristotle in his book on the human
soul, De Anima, Ibn Sina thought the act of abstraction occurs when the individual human mind is
illuminated by something called the “Active” or “Agent Intellect”. Our individual minds ibn Sina called
“possible” (meaning passive or receptive). The active intellect is a kind of cosmic intellect, emanating from
God, that comes to us when we recognize and reason by means of universal concepts. We’ll examine the
problem of the relationship between the Active Intellect and the individual soul in the next section, when we
turn to ibn Rushd.

II. Ibn Rushd on The Agent Intellect

The theory of the active or “agent” intellect was developed in response to three ideas from Aristotle’s
philosophy of the mind:

1. That man, unlike all other animals, possesses a capacity for rational, scientific knowledge.
2. The presence of this rational capacity cannot be explained in physical or biological terms: yet, the
individual human soul is simply the actualization of the human body’s biological capacities. Hence,
rationality must somehow enter the human soul from the outside.
3. Rational mind is immaterial and simple and, therefore, naturally indestructible. Since the rational mind
exists outside the individual human soul, the immortality of Mind does not guarantee the immortality of the
individual personality.

The crucial question that divides the al-falsafa philosophers is this: when the agent intellect illuminates the
individual human soul, does it give rise to an enduring individual intellect? Ibn Sina argues that it does, and,
on this basis, he affirmed the immortality of the individual human soul. Because the human soul is lifted
from the merely physical and biological domain by the illumination of the Agent Intellect, the individual
human soul shares in the simplicity and immateriality, and, therefore, in the immortality and
indestructibility of the Agent Intellect.

In contrast, ibn Rushd argued that, throughout the process of illumination, the individual soul remains
entirely passive and receptive. It is the Agent Intellect that engages in all rational, scientific thinking in and
through the individual human being. This activity doesn’t engender any capacity for rational thought within
the individual human being. Consequently, when a human being dies, the soul dies with him or her, just as
the animal or plant “soul” dies along with the organism. (Ibn Rushd did, however, agree with the Koran that
there would be a resurrection of the body.)

III. Aquinas on Knowledge (Epistemology) and the Soul

A. What are we doing when we philosophize about knowledge?

There are, broadly speaking, two ways of thinking about epistemology (or the philosophy of knowledge).
We could think of it as primarily concerned with skeptics and skepticism. Skeptics deny that we know
anything. Some even deny that some opinions are more reasonable than others. One could take the task of
epistemology to be the refutation of skeptics: coming up with proofs that we do know some things, proofs
that are so powerful and undeniable that the skeptic will be forced to agree.

This is the way most “modern” philosophers (from the time of Rene Descartes in the 16

th

century until the

early or mid-20

th

century) did think about epistemology. In this respect, Augustine was something of a

“modern” philosopher, because he too tried to refute the skeptic by means of an argument very similar to

Descartes’s: if I doubt (as the skeptic recommends), then at least I know that I doubt, and no amount of
further doubting can possibly deprive me of this certainty.

Descartes’s motivation for taking epistemology this way depends, I believe, on the fact that Descartes (and
other 16

th

century thinkers like Francis Bacon and Galileo) introduced a new distinction between

“philosophy” and “science”. Science was concerned with the description and explanation of physical
phenomena by means of mathematics (especially geometry). Descartes divided reality into two separate
components: souls and matter. Science tells us all there is to know about matter, and we can know all there is
to know about our souls by simple introspection. What then, is left for “philosophy” to do? Descartes’s
answer was this: science takes certain things for granted (like the reliability of our senses and of our
mathematical judgments). Science cannot defend itself against skeptics who think that all our sense data and
all our mathematical intuitions may be illusions. So, philosophy’s job is to refute the skeptic by arguments so
powerful that the skeptic simply cannot deny them. On this view, epistemology is a kind of super-science, a
science that must be completed before any other science can proceed with any confidence.

This modern epistemological project was, in my judgment and in the judgment of most (but not all)
contemporary philosophers, a total and catastrophic failure. Around the turn of the 19

th

and 20

th

centuries, a

number of philosophers (including G. E. Moore, Ludwig Wittgenstein, and the American W. V. O. Quine)
began to move back toward a more classical conception of epistemology, according to which epistemology is
just one part of our knowledge of reality. On this view, epistemology does not come “before” the other
sciences or branches of philosophy, nor do they come entirely “before” epistemology. Instead (to use Oscar
Neurath’s metaphor), we are on a raft in the middle of an ocean, the various rafts representing the various
sciences and branches of philosophy at their current stage of development. It would be crazy to jump off the
raft and to try to build a new and better one from scratch in the middle of the ocean, which is in effect what
Descartes and his modern followers tried to do. Instead, we should recognize that all our opinions are
fallible and tentative, including those of epistemology.

Aquinas’s approach to epistemology is like that of Moore, Wittgenstein and Quine, and radically unlike that
of Descartes and such other “modern” philosophers as David Hume and Immanuel Kant (of the 18

th

century). Aquinas isn’t concerned with refuting the skeptic. He takes it as obvious that we know many
things: the job of philosophy is to explain how this is possible, to describe accurately the causes and nature of
human knowledge, not to prove beyond all doubt that it actually exists.

This means that Aquinas is free to use everything he knows about human beings and the world they inhabit,
whether the source of that knowledge be the senses, the Scriptures, common sense, or scientific discovery.
The sources don’t have to be absolutely indubitable before the epistemologists can legitimately use them as
data for this theorizing.

B. Human Knowledge vs. Angelic Knowledge

Whether or not angels actually exist, we can conceive of beings who know everything they know by direct
vision of the truths as they flow from God’s essence and creative will. Such angels could know both
universal facts (like the laws of nature) and particular facts (e.g., of geography, history or biography) simply
by knowing what kind of world God has chosen to create. They wouldn’t need to go out and collect
information about these things, since they would fully understand their causes within God’s will.

Aquinas takes it as obvious that human beings (at least, this side of death) aren’t at all like that. Our
intellectual powers are far weaker: we can’t grasp God’s nature, and we have no direct access to His will. We
need information from another source. Fortunately, we do have such a source: the five senses. Following
Aristotle, Aquinas goes so far as to say that all of our understanding comes to us through the senses: apart
from sensory information, our intellect is a “blank slate” (tabula rasa). However, unlike some modern
“empiricists” (like David Hume), Aquinas did not think that our knowledge begins and ends with the senses.
Thanks to the information about particular things provided by the senses, we are able to rise eventually to
the knowledge of universal truths, such as the laws of mathematics, physics and metaphysics.

Aquinas’s epistemology is very much influenced by his attempted solution to the problem of universals. In
order to have universal knowledge, we must have knowledge of universals (of the common essences and
natures of things). However, Aquinas rejects extreme realism: he doesn’t believe that the universals are

things in their own right, existing independently of particulars. In fact, as Abelard argued, universals as such
exist only in our minds (and those of other intellectual beings, like the angels). Following Philo, Augustine
and many others, Aquinas replaces Plato’s eternal Forms or Ideas with eternal types within the mind of God.
(How is this compatible with God’s absolute simplicity? That’s a tough problem.)

So, there are universals in God’s mind and ours (particular ideas that can be predicated of many things), and
otherwise everything is particular. Nonetheless, things come with “common natures”, the essences-
considered-absolutely, which have a merely logical being, and which suffer from an extreme sort of logical
incompleteness (they are neither one nor many, neither universal nor particular, and so on).

How do these common natures move from their existence as particulars in the real world to an existence as
universals in our minds? By the following two-step process:

1. The sensible (visible, tangible, smellable, tasteable, audible) object acts upon our sense organs, producing
an image (which Aquinas calls a “phantasm”) within our bodies. The image of a red thing needn’t itself be
red (anymore than the image of a sharp thing need be sharp, or the image of a cube be cubical): instead the
phantasm represents the characteristics of the external object.

1

These representations are normally accurate,

but can be distorted in various ways (by disease, malformation or abnormal environments).

2. The active intellect “sees” or “apprehends” these phantasms within its body and extracts or “abstracts” the
essence (called the “intelligible species”), placing this intelligible species within a receptacle called the
“passive intellect”. The intelligible species are universals, present within the mind. The species make the
corresponding kind of thing into an object of knowledge: when we have the species man within our passive
intellect, we are enabled to understand what men are (i.e., the natures of the real, particular men).

Once we have universals within our minds, we can do two further things: we can make various judgments,
forming propositions that we accept as true; and we can engage in reasoning, inferring new truths from old
ones. At this point, Aquinas comes closer to Augustine’s divine-illumination model: he says that we make
these judgments by means of an inner intellectual “light”, which we have by our participation in the divine,
uncreated light of God. We are able to make mostly reliable judgments because God has made us in His
image, placing within us a kind of likeness of his own power of understanding. However, there are two
limitations imposed on us by our human nature: we depend on the senses to provide us with the intelligible
species, and we also depend on the senses to provide us with the basis for making judgments about
particular things (like ‘Socrates is sitting’).

Aquinas makes very clear (in Q85, A2) that we know real, external things by means of the intelligible species
in our minds: we don’t only, or even primarily or in the first instance, know the species within our minds.
That is, I know what men are by virtue of having the intelligible species of man within my mind. I may have,
however, no idea that such a thing as an intelligible species exists at all. It is only through philosophical
thought and reflection that I come to recognize that my mind actually contains such things. The first and
primary object of my knowledge is the “external world”, the world of sensible objects. In this way, Aquinas
avoid the slide into “idealism” that was so typical of philosophers in the 16

th

through 19

th

centuries. Idealists

think that all I can know for sure are the contents of my own mind. I have to make guesses (perhaps wild,
unsubstantiated guesses) about whether anything really exists outside my mind that these ideas represent.
For Aquinas, this is all backward. I wouldn’t even know that I had a mind or any ideas within it if I didn’t
first know many things about the real, external world by means of my five senses.

The two step-process mentioned above is Aquinas’s sketch of how it is possible for human knowledge to get
started. The sketch makes it sound as though acquiring understanding is very simple: just look around,
gather some sense experience, and –- Swoosh! –- your active intellect will swoop down and extract some
universals. In other words, we might take Aquinas as giving us a simple, two-step recipe for discovering the
true essences of things: 1. Observe. 2. Think.

1

There is some difference in interpretation on this point, but I agree with Norman Kretzmann in thinking that the most

reasonable interpretation does not require the sensible species to have in reality the form it represents. See his paper on
Aquinas’s philosophy of mind in the Cambridge Companion to Aquinas.

In fact, Aquinas does indeed recommend these two activities, and in doing so, he is providing genuine
science with its proper foundation. Many philosophers have recommended that we limit ourselves to just
observing without thinking or just thinking without observing, or, indeed, to do neither. Nonetheless,
Aquinas was under no illusions about how difficult it is to discover the true essence of a thing. He said,
famously, that no philosopher had yet understood anything so simple as a fly. (We now have some idea how
true this was.) You can stare at water all day, drink it and swim in it even, and your active intellect won’t
just pull H

2

O out of your experience with no further ado. Aquinas recognized that, before the active intellect

can act, we must accumulate enough experience, and experience of the right kind. It takes investigation,
experimentation, collation and comparison, and many other activities before we can be in a position to
abstract fully the essence of a sensible thing.

Aquinas insists that scientific knowledge is a possibility, given the right combination of experience and
analysis. In this respect, he is on the side of science (physics, chemistry and so on) and against those skeptics
who undermine the confidence needed to pursue the “dream of a final theory” (as our own Steven Weinberg
puts it).