60 ARISTOTLE
by which we come to know them
(the latter being the fundamental
quesion of “epistemology”, or the
theory of knowledge). And it was
this difference of opinion on how
we arrive at universal truths that
later divided philosophers into two
separate camps: the rationalists
(including René Descartes,
Immanuel Kant, and Gottfried
Leibniz), who believe in a priori,
or innate, knowledge; and the
empiricists (including John Locke,
George Berkeley, and David Hume),
who claim that all knowledge
comes from experience.Biological classification
The manner in which Plato and
Aristotle arrive at their theories tells
us much about their temperaments.
Plato’s theory of Forms is grand and
otherworldly, which is reflected in
the way he argues his case, using
highly imaginative fictionalized
dialogues between Socrates and
his contemporaries. By contrast,
Aristotle’s theory is much more
down to earth, and is presented in
more prosaic, academic language.
Indeed, so convinced was Aristotlethat the truth of the world is to be
found here on Earth, and not in
some higher dimension, that he set
about collecting specimens of flora
and fauna, and classified them
according to their characteristics.
For this biological classification,
Aristotle devised a hierarchical
system—the first of its kind, and so
beautifully constructed that it forms
the basis of the taxonomy still in
use today. First, he divides the
natural world into living and
nonliving things, then he turns his
attention to classifying the living
world. His next division is between
plants and animals, which involves
the same kind of thinking that
underpins his theory of universal
qualities: we may be able to
distinguish between a plant and
an animal almost without thinking,
but how do we know how to make
that distinction? The answer, for
Aristotle, is in the shared features
of either category. All plants share
the form “plant”, and all animals
share the form “animal.” And once
we understand the nature of those
forms, we can then recognize them
in each and every instance.
This fact becomes more apparent
the more Aristotle subdivides the
natural world. In order to classify a
specimen as a fish, for example, we
have to recognize what it is that
makes a fish a fish—which, again,
can be known through experience
and requires no innate knowledge
at all. As Aristotle builds up a
complete classification of all living
things, from the simplest organisms
to human beings, this fact is
confirmed again and again.Teleological explanation
Another fact that became obvious
to Aristotle as he classified the
natural world is that the “form”
of a creature is not just a matter
of its physical characteristics, suchAll men by nature
desire to know.
AristotleBy studying particular things,
therefore, we can gain insight into
their universal, immutable nature.
What is true of examples in the
natural world, Aristotle reasons,
is also true of concepts relating
to human beings. Notions such
as “virtue”, “justice”, “beauty”, and
“good” can be examined in exactly
the same way. As he sees it, when
we are born our minds are like
“unscribed tablets”, and any ideas
that we gain can only be received
through our senses. At birth, we
have no innate ideas, so we can
have no idea of right or wrong. As
we encounter instances of justice
throughout our lives, however, we
learn to recognize the qualities that
these instances have in common,
and slowly build and refine our
understanding of what justice is.
In other words, the only way we
can come to know the eternal,
immutable idea of justice, is by
observing how it is manifested
in the world around us.
Aristotle departs from Plato,
then, not by denying that universal
qualities exist, but by questioning
both their nature and the means
Aristotle classified many of the
different strands of knowledge and
learning that we have today, such
as physics, logic, metaphysics, poetics,
ethics, politics, and biology.