Summary
The Categories, traditionally interpreted
as an introduction to Aristotle’s logical work, divides all of being
into ten categories. These ten categories are as follows:
Substance, which in this context means what something
is essentially (e.g., human, rock)
- Quantity (e.g., ten feet, five liters)
- Quality (e.g., blue, obvious)
- Relation (e.g., double, to the right of)
- Location (e.g., New York, home plate)
- Time (e.g., yesterday, four o’clock)
- Position (e.g., sitting, standing)
- Possession (e.g., wearing shoes, has a blue coat)
- Doing (e.g., running, smiling)
- Undergoing (e.g., being run into, being smiled at)
Of the ten, Aristotle considers substance to be primary,
because we can conceive of a substance without, for example, any
given qualities but we cannot conceive of a quality except as it
pertains to a particular substance. One important conclusion from
this division into categories is that we can make no general statements
about being as a whole because there are ten very different ways
in which something can have being. There is no common ground between
the kind of being that a rock has and the kind of being that the
color blue has.
Aristotle’s emphasis on the syllogism leads him to conceive
of knowledge as hierarchically structured, a claim that he fleshes
out in the Posterior Analytics. To have knowledge
of a fact, it is not enough simply to be able to repeat the fact.
We must also be able to give the reasons why that fact is true,
a process that Aristotle calls demonstration. Demonstration
is essentially a matter of showing that the fact in question is
the conclusion to a valid syllogism. If some truths are premises
that can be used to prove other truths, those first truths are logically
prior to the truths that follow from them. Ultimately, there must
be one or several “first principles,” from which all other truths
follow and which do not themselves follow from anything. However,
if these first principles do not follow from anything, they cannot
count as knowledge because there are no reasons or premises we can
give to prove that they are true. Aristotle suggests that these first
principles are a kind of intuition of the universals we recognize in
experience.
Aristotle believes that the objects of knowledge are also
structured hierarchically and conceives of definition as largely
a process of division. For example, suppose we want to define human.
First, we note that humans are animals, which is the genus to which
they belong. We can then take note of various differentia, which
distinguish humans from other animals. For example, humans walk
on two legs, unlike tigers, and they lack feathers, unlike birds.
Given any term, if we can identify its genus and then identify the
differentia that distinguish it from other things within its genus,
we have given a definition of that term, which amounts to giving
an account of its nature, or essence. Ultimately, Aristotle identifies
five kinds of relationships a predicate can have with its subject:
a genus relationship (“humans are animals”); a differentia relationship
(“humans have two legs”); a unique property relationship (“humans
are the only animals that can cry”); a definition, which is a unique
property that explains the nature or essence of the subject; and
an accident relationship, such as “some humans have blue eyes,”
where the relationship does not hold necessarily.
While true knowledge is all descended from knowledge of
first principles, actual argument and debate is much less pristine.
When two people argue, they need not go back to first principles
to ground every claim but must simply find premises they both agree
on. The trick to debate is to find premises your opponent will agree
to and then show that conclusions contrary to your opponent’s position follow
necessarily from these premises. The Topics devotes
a great deal of attention to classifying the kinds of conclusions
that can be drawn from different kinds of premises, whereas the Sophistical Refutations explores
various logical tricks used to deceive people into accepting a faulty
line of reasoning.
