other) as well as
poets works, might be contained in a nutshell.

27. When not so used, the Variation is to be explained.

But after all, the provision of words is so scanty in respect to that
infinite variety of thoughts, that men, wanting terms to suit their
precise notions, will, notwithstanding their utmost caution, be forced
often to use the same word in somewhat different senses. And though in
the continuation of a discourse, or the pursuit of an argument, there
can be hardly room to digress into a particular definition, as often
as a man varies the signification of any term; yet the import of the
discourse will, for the most part, if there be no designed fallacy,
sufficiently lead candid and intelligent readers into the true meaning
of it; but where there is not sufficient to guide the reader, there it
concerns the writer to explain his meaning, and show in what sense he
there uses that term.

BOOK IV

OF KNOWLEDGE AND PROBABILITY SYNOPSIS OF THE FOURTH BOOK.

Locke's review of the different sorts of ideas, or appearances of what
exists, that can be entertained in a human understanding, and of their
relations to words, leads, in the Fourth Book, to an investigation of
the extent and validity of the Knowledge that our ideas bring within our
reach; and into the nature of faith in Probability, by which assent is
extended beyond Knowledge, for the conduct of life. He finds (ch. i, ii)
that Knowledge is either an intuitive, a demonstrative, or a sensuous
perception of absolute certainty, in regard to one or other of four
sorts of agreement or disagreement on the part of ideas:--(1) of each
idea with itself, as identical, and different from every other; (2) in
their abstract relations to one another; (3) in their necessary
connexions, as qualities and powers coexisting in concrete substances;
and (4) as revelations to us of the final realities of existence. The
unconditional certainty that constitutes Knowledge is perceptible by man
only in regard to the first, second, and fourth of these four sorts: in
all general propositions only in regard to the first and second; that is
to say, in identical propositions, and in those which express abstract
relations of simple or mixed modes, in which nominal and real essences
coincide, e. g. propositions in pure mathematics and abstract morality
(chh. iii, v-viii). The fourth sort, which express certainty as to
realities of existence, refer to any of three realities.