as middle in universal importance and they are preceded
and followed by two pairs of ancillary treatises, the Cate-
gories and On Interpretation as major extremes and the
Topics and Sophistical Refutations as minor extremes.

To understand the prior and posterior resolution of scien-
tific argumentation back to its ultimate constituents certain
concepts and terms must be familiar and the proper com-
bination of them into judgments expressed in propositions
must be known. Once we grasp the overall picture of what
science involves, then we are able to see the reason for a
preliminary discussion of concepts-terms and judgments-
propositions. One could not understand the formal pattern
of correct reasoning nor the ingredients of science, in the
strict sense, unless he be aware of the implications of certain
simple, univocal terms predicable of a subject and indi-
cating basic and irreducible scientific categories of classi-
fication. The distinction of the categories must be clear as
regards their essence, properties and applicabilities since
they are the ingredients of science. Moreover, there is a
fundamental opposition between science and opinion, the
subject-matter of the Topics, which cannot be understood
if the nature and types of opposition are not known. The
premises of a syllogism are prior to the conclusion in one
sense and, yet, science is simultaneous with the premises,
in another. What do we mean by 'prior'? What do we
mean by 'simultaneous'? Science is a quality of mind ac-
quired by an alteration which is a kind of movement. How
does this type of movement differ from the other five
varieties? Again, one may be said to have or to possess
science. In what way does one have a habit of conclusions?
Certainly, not in the way in which one is said to have a
wife or a coat or a ring on his finger.

Of the fifteen chapters compiled together as The Cate-
gories six (4-9) take up and explain the categories proper
and one each is devoted to the following: the way terms
are related to things, the two forms of speech and the dis-
tinctions between to be present in and predicable of some-

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