Philosophy was defined by the Stoics as 'the knowledge of things
divine and human'. It was divided into three departments; logic,
ethic, and physic. This division indeed was in existence before their
time, but they have got the credit of it as of some other things
which they did not originate. Neither was it confined to them, but
was part of the common stock of thought. Even the Epicureans, who are
said to have rejected logic can hardly be counted as dissentients
from this threefold division. For what they did was to substitute for
the Stoic logic a logic of their own, dealing with the notions
derived from sense, much in the same way as Bacon substituted his
Novum Organum for the Organon of Aristotle. Cleanthes we are told
recognised six parts of philosophy, namely, dialectic, rhetoric,
ethic, politic, physic, and theology, but these are obviously the
result of subdivision of the primary ones. Of the three departments
we may say that logic deals with the form and expression of
knowledge, physic with the matter of knowledge, and ethic with the
use of knowledge. The division may also be justified in this way.
Philosophy must study either nature (including the divine nature) or
man; and, if it studies man, it must regard him either from the side
of the intellect or of the feelings, that is either as a thinking
(logic) or as an acting (ethic) being.
As to the order in which the different departments should be studied,
we have had preserved to us the actual words of Chrysippus in his
fourth book on Lives. 'First of all then it seems to me that, as has
been rightly said by the ancients, there are three heads under which
the speculations of the philosopher fall, logic, ethic, physic; next,
that of these the logical should come first, the ethical second, and
the physical third, and that of the physical the treatment of the
gods should come last, whence also they have given the name of
"completions" to the instruction delivered on this subject'. That
this order however might yield to convenience is plain from another
book on the use of reason, where he says that 'the student who takes
up logic first need not entirely abstain from the other branches of
philosophy, but should study them also as occasion offers.'
Plutarch twits Chrysippus with inconsistency, because in the face of
this declaration as to the order of treatment, he nevertheless says
that morals rest upon physics. But to this charge it may fairly be
replied that the order of exposition need not coincide with the order
of existence. Metaphysically speaking, morals may depend upon physics
and the right conduct of man be deducible from the structure of the
universe but for all that, it may be advisable to study physics
later. Physics meant the nature of God and the Universe. Our nature
may be deducible from that but it is better known to ourselves to
start with, so that it may be well to begin from the end of the stick
that we have in our hands. But that Chrysippus did teach the logical
dependence of morals on physics is plain from his own words. In his
third book on the Gods he says 'for it is not possible to find any
other origin of justice or mode of its generation save that from Zeus
and the nature of the universe for anything we have to say about good
and evil must needs derive its origin therefrom', and again in his
Physical Theses, 'for there is no other or more appropriate way of
approaching the subject of good and evil on the virtues or happiness
than from the nature of all things and the administration of the
universe--for it is to these we must attach the treatment of good and
evil inasmuch as there is no better origin to which we can refer them
and inasmuch as physical speculation is taken in solely with a view
to the distinction between good and evil.'
The last words are worth noting as showing that even with Chrysippus
who has been called the intellectual founder of Stoicism the whole
stress of the philosophy of the Porch fell upon its moral teaching.
It was a favourite metaphor with the school to compare philosophy to
a fertile vineyard or orchard. Ethic was the good fruit, physic the
tall plants, and logic the strong wall. The wall existed only to
guard the trees, and the trees only to produce the fruit. Or again
philosophy was likened to an egg of which ethic was the yolk
containing the chick, physic the white which formed its nourishment
while logic was the hard outside shell. Posidonius, a later member of
the school, objected to the metaphor from the vineyard on the ground
that the fruit and the trees and the wall were all separable whereas
the parts of philosophy were inseparable. He preferred therefore to
liken it to a living organism, logic being the bones and sinews,
physic the flesh and blood, but ethic the soul.