Socrates thought that the method of procedure in the
acquisition of science must be changed if the errors of the
Pre-Socratics were to be avoided. He sought exact defini-
tions, especially in the field of morality, which seemed to
him to deserve the main, if not the only, attention of man.
The procedural activity for the acquisition of these stable,
eternal essences of things was induction. According to
Aristotle this was, indeed, Socrates' greatest claim to pre-
eminence as a philosopher: to have seen that the important
thing in science is the essence, expressible in a definition
and that the only valid way of acquiring an understanding
of the essences of things was by the inductive procedure of
examining individual instances in variable circumstances.
For Aristotle this implied the possession by man of an
abstractive or separative function in the employment of
which he was enabled to go from the multiple individual
instances presented in experience to the universal law appli-
cable to each.

Plato strove to perfect the Socratic method and, also to
apply it to the whole of science as well as to the area of
ethical conduct. But in his attempt to universalize the
method he erred greatly, according to Aristotle, by sepa-
rating the world of essential natures from the world of
sensibly perceived realities and thus by setting up an
isolated intelligible realm of Ideal-Forms. That hypothesis,
which he nowhere proves, leads to absurdity and, as a
matter of fact, is quite useless from the scientific point of
view. Maybe Plato did not see how any other hypothesis
could explain both the mutability of sense objects and the
stability of science. But it is absurd to place the essence of
a thing outside the thing of which it is the essence. If Ideal-
Forms are required to explain the existence of the one as
regards the many, why, then, are there not Ideas of all the
universals, which are instances of the one among the many?
Why are there not Ideas of accidents, of negations, of priva-

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