on his
part, the various facts would get together in new combinations and
suggest explanations that neither he nor any one else had ever thought
of before. Third, our would-be scientific investigator may lack the
clear, steady vision to see the consequences of his hypothesis; and,
fourth, he may lack the enterprise to go out and look for the facts
that his hypothesis tells him should be found.

Psychology and Logic

Psychology is not the only science that studies reasoning; that is the
subject-matter of logic as well, and logic was in the field long
before psychology. Psychology studies the _process_ of reasoning,
while logic checks up the result and shows whether it is valid or not.
Logic cares nothing about the exploratory process that culminates in
inference, but limits itself to inference alone.

Inference, in logical terminology, consists in drawing a conclusion
from two given premises. The two premises are the "two facts" which,
acting together, arouse the {476} perceptive response called
inference, and the "third fact" thus perceived is the conclusion.
[Footnote: The "two facts" or premises need not be true; either or
both may be assumed or hypothetical, and still they may lead to a
valid conclusion, i.e., a conclusion implicated in the assumed
premises.] Logic cares nothing as to how the premises were found, nor
as to the motive that led to the search for them, nor as to the time
and effort required, nor the difficulty encountered; these matters all
pertain to psychology.

Logic sets forth the premises and conclusion in the form of the
"syllogism", as in the old stand-by:

Major premise: All men are mortal
Minor premise: Socrates is a man
Conclusion: Therefore, Socrates is mortal

The syllogism includes three "terms", which in the above instance are
"Socrates", "mortal", and "man" or "men". Logic employs the letters,
S, P, and M to symbolize these three terms in general. S is the
"subject" (or, we might say, the "object" or the "situation") about
which something is inferred. P is the "predicate", or what is inferred
about S; and M is the "middle term" which corresponds to our
"yardstick" or "point of reference", as we used those words at the
beginning of the chapter. S is compared with P through the medium of
M; or, S and P are both known to be related to M, and therefore (when
the relations are of the right sort) they are related to each other.
It is part of the business of logic to examine