St. Thomas Aquinas’
Epistemology
• Life
– Born 1225
– Son of a Count
– Joined the then new, mendicant
religious order, the Dominicans, in
1244
– Studied in Cologne, Germany under
St. Albert the Great. Received
Doctorate in 1256.
– Taught at the Sorbonne (the University
of Paris) 1256-1259 & 1269-1272
– Taught at the University of Naples
1272-1274
– Died 1274 while on journey to a
Church council.
– Canonized 1323
• Influence
– The leading philosopher of the
Aristotelian revival in Europe during
the High Middle Ages.
– Philosopher of Common Sense.
– Sought to integrate Aristotelian
philosophy with Christianity.
– Greatest work Summa Theologica,
written 1265-1272 and left unfinished
at his death.
– Portion of the Summa dealing with
epistemology written around 1268.
– As with all his philosophy, Aquinas’
epistemology rooted in Aristotle’s.
• Locke’s First Mistake
– “[B]efore I proceed on to what I have
thought on this subject, I must here,
in the entrance, beg pardon of my
reader for the frequent use of the
word idea, which he will find in the
following treatise. It being that term
which, I think, serves best to stand for
whatsoever is the object of the
understanding . . . .”
John Locke, An Enquiry Concerning Human
Understanding (1690)
– Locke maintains that the objects of
human knowledge, i.e. what humans
know, are ideas.
– Aquinas’ anticipates Locke’s view:
• “Some have asserted that our
intellectual faculties know only the
impression made on them . . . .
According to this theory, the
intellect understands only its own
impression, namely, [its idea].”
Summa Theologica, I, 85, ii
– Locke’s view about the object of
knowledge leads to his
Representative Theory of Perception,
i.e. that, within the minds of humans,
there are ideas that are
representations, or copies, of material
objects.
– Now, when you think about it, it’s
rather strange for Locke to say that
what humans know are ideas.
– In ordinary language humans say, for
example, “I see the table.” That
statement, on the face of it, indicates the
object of sight is the table.
– On Locke’s view, however, the object of
sight is not really the table but an idea of
the table.
– Locke’s view leads to the Egocentric
Predicament, i.e. problem of not being
able to tell whether the idea of the table
accurately corresponds to the table or,
for that matter, anything else.
• “If all we knew . . . directly were our
own ideas, skepticism would be
inevitable . . . ; for, we would be like
prisoners in jail cells, seeing only
pictures of the outside world on TV
screens and never able to get out
of jail and see the real world
directly to know whether the TV
images are true or false.”
Peter Kreeft, Footnote 84 in Summa of
the Summa, p. 324
– Another problem with Locke’s view is that
it leads, inevitably, as we have seen, to
relativism.
• “[This view of the object of knowledge] is
untrue, because it would lead to the
opinion of the ancients [the Protagorians]
who maintained that “whatever seems, is
true” [Aristotle, Metaphysics. iii. 5], and
that, consequently, contradictories are
true simultaneously. For, if the faculty
knows its own [idea] only, it can judge of
that only . . . . Thus, every opinion would
be equally true . . . .”
Summa, I, 85, ii
• In this response, we see how Aquinas is a
Philosopher of Common Sense.
• He takes it to be common sense that
inconsistent claims cannot all be true, e.g.
‘John’s birthday is December 2’ and ‘John’s
birthday is December 3.’
• He does not reject the common sense
notion of truth, as the Post-Modernists do,
so that inconsistent claims can all be true.
• Rather, he rejects any premise that leads to
a conclusion contrary to common sense.
• In this case, Aquinas rejects Locke’s
premise that ideas are the objects of
knowledge.
– Since Aquinas rejects Locke’s
premise that ideas are the objects of
knowledge, what does he believe are
the objects of knowledge?
– For Aquinas, the objects of
knowledge, in the first instance, are
the external, material objects that
humans know through perception.
– As indicated before, this view
accords better with ordinary
language.
– Humans say “I see the table,” not “I
see an idea which is a copy of the
table.”
– Since Aquinas’ view accords better
with ordinary language, it, thereby,
accords better with common sense.
– Thus, in his judgment, Aquinas’ view
is superior to Locke’s
– Ideas (or, as Aquinas prefers,
phantasms) play a role in perception,
but not the role Locke assigned to
them.
– Phantasms, or ideas, are NOT what
(id quod) humans know; rather, they
are the means by which (id quo)
humans know.
– To put it metaphorically, phantasms
(ideas) are not what the human mind
knows; rather, they are the “windows”
by means of which the human mind
becomes aware of the material
objects of the external world.
– With this understanding of the role
that ideas play in perception, Aquinas
avoids Post-Modernism.
• Locke’s Second Mistake
– Recall Locke’s metaphor for the
human mind.
– It is a tabula rasa, a blank slate on
which experience “writes.”
– By this image, Locke indicates that the
human mind is entirely passive.
– In coming to know, the human mind
does NOT do anything.
– It just sits there, like a blank table,
and lets experience “write” ideas on it.
– This view of how humans come to
know is at odds with the way humans
normally speak.
– For example, humans say “I see the
table.” This indicates that I am
actively doing something rather than
just sitting passively, like a blank
tablet, while something is done to me.
– As indicated before, Aquinas
maintains that an analysis of how
humans come to know according
better with ordinary language would
be a more common sense analysis
and, therefore, a better one.
– Thus, in Aquinas’ analysis of how
humans come to know, the mind is
active, not passive.
– The Theory of Abstraction
• “The Philosopher [Aristotle] says
[De Anima iii, 4] that things are
intelligible in proportion as they are
separate from matter. Therefore,
material things must needs be
understood according as they are
abstracted from matter and from
material images, namely,
phantasms.”
Summa, I, 85, i
• As this quote indicates, Aquinas’
Theory of Abstraction is a
development of Aristotle’s.
• Recall that Aristotle maintained that
external objects are substances
and substances are composite
realities.
• Substances are the union of matter
and form.
• In reality, matter and form are never
separated.
• That is, in reality, one never finds
form with matter, nor matter without
form.
• Within the human mind, however,
the two can be separated.
• How abstraction works:
– In perception, by means of
phantasms, humans come to
know particular substances.
– The mind then abstracts from
the phantasms whatever is
common to them.
– “[T]he things which belong to the
species [form] of a material thing –
such as a stone, or a man, or a horse
– can be thought of apart from the
individualizing principle [matter] . . . .
This is what we mean by abstracting
the universal from the particular, or
the intelligible species [form] from the
phantasm; that is, by considering the
nature of the species [form] apart
from its individual qualities [matter]
[perceived by means of] the
phantasms”
Summa, I, 85, i
– “‘Appleness’ exists only in
individual apples. But, the
intellect can abstract, or focus,
on the form alone without the
matter; thus, the form as known
is universal (for matter is what
individuates form). Universality
is in the mind, not in the world.”
Peter Kreeft, Footnote 89 in
Summa of the Summa, p. 327
• It is by means of his Theory of
Abstraction, that Aquinas avoids
Hume’s skepticism.
– Since abstraction “enhances”
perception, humans can truly
know universal natures.
– By examining universal natures,
humans can come to know how
these natures necessarily relate
to one another.
– As a result, the Principle of
Universal Causation is based on
more than just the constant
conjunction of particular events.
– It is based upon the necessary
relationships that exist between
universal natures.
– For example, given its nature,
when a marker is dropped within
a gravitational field strong
enough, it will fall toward the
center of that field.
– Thus, given both the nature of the
marker and the nature of gravity,
gravity necessarily causes the pointer
to fall.
• Final Thoughts
– By rooting his analysis of human knowledge
in common sense, Aquinas avoids both
Hume’s radical skepticism and PostModernism.
– Although it is rooted in common sense,
Aquinas’ analysis goes far beyond it. Thus,
it is truly philosophical.
– What else should be expected from a
Philosopher of Common Sense?