Summary
Book Theta discusses potentiality and actuality, considering
these concepts first in regard to process or change. When one thing,
F, changes into another, G, we can say that F is G in potentiality,
while G is G in actuality. F changes into G only if some other agent,
H, acts on it. We say that H has active potentiality and F has passive
potentiality. Potentiality can be either rational or irrational,
depending on whether the change is effected by a rational agent
or happens naturally. Aristotle distinguishes rational potentiality
from irrational potentiality, saying that rational potentiality
can produce opposites. For example, the rational potentiality of
medicine can produce either health or sickness, whereas the irrational
potentiality of heating can produce only heat and not cold. All
potentialities must eventually be realized: if a potentiality never
becomes an actuality, then we do not call it a potentiality but
an impossibility. A potentiality is also determinate, meaning that
it is the potential for a particular actuality and cannot realize
some other actuality. While irrational potentialities are automatically
triggered when active and passive potentialities come together,
this is not the case with rational potentialities, as a rational
agent can choose to withhold the realization of the potentiality
even though it can be realized.
Aristotle identifies actuality with form, and hence substance, while
identifying matter with potentiality. An uncarved piece of wood,
for example, is a potential statue, and it becomes an actual statue
when it is carved and thus acquires the form of a statue. Action
is an actuality, but there are such things as incomplete actions,
which are also the potentiality for further actions. Aristotle distinguishes
between incomplete and complete actions by saying that incomplete
actions do not contain their purpose within them, while the latter
do. For example, dancing is a complete action because it is an end
in itself, whereas fetching wood for a fire is an incomplete action
because the end of fetching wood is to create a fire. If one thing
can turn into another, that first thing is always potentially the
other. That means that anything is potentially something else and
that it was something else in the past with the potential to become
what it is now. Aristotle speculates about the existence of an ultimate
matter, which is potentially anything.
Aristotle argues that actuality is more fundamental than
potentiality for three reasons. First, we cannot think of something
as a potentiality without also thinking of the actuality it can
potentially become, but we can think of an actuality without thinking
of its potentiality. Second, for something to be potentially something
else, that something else must already exist in actuality or there
would be nothing for that potentiality to become. Third, Aristotle
identifies actuality with form, which is in turn related to substance,
which is the most fundamental thing that there is.
Book Iota treats the topic of unity, which is important
to Aristotle because he has argued in book Zeta that both a substance
and its definition are unities. Unity itself, however, is not a
substance for two reasons. First, unity is a universal, not a species.
Second, unity is always a property of something else: there is one
table, one person, one chair, but never the number one by itself.
The discussion of unity leads into a discussion of contrariety, which
Aristotle defines as a maximum of difference and can only hold between
two extremes. Two species of the same genus differ from one another
in having contrariety in their forms. For example, one animal that
has wings and one that does not have wings are different species
within the genus animal. On the other hand, men and women are not
of different species because the contrariety that exists between
them is on the level of matter, not form.
Book Kappa, which some scholars doubt was even written
by Aristotle, consists mostly of repeating doctrines already enunciated in
the Physics or in earlier books of the Metaphysics.
