— 576 —
When mental Propositions contain real Truth, and when verbal.
      §6. Every one’s Experience will satisfie him, that the Mind,
either by perceiving or supposing the Agreement or Disagreement
of any of its Ideas, does tacitly within it self put them into a kind
of Proposition affirmative or negative, which I have endeavoured to
express by the terms Putting together and Separating. But this Action
of the Mind, which is so familiar to every thinking and reasoning
Man, is easier to be conceived by reflecting on what passes in us,
when we affirm or deny, than to be explained by Words. When a
Man has in his Mind the Idea of two Lines, viz. the Side and Diagonal
of a Square, whereof the Diagonal is an Inch long, he may have the
Idea also of the division of that Line, into a certain number of equal
parts; v.g. into Five, Ten, an Hundred, a Thousand, or any other
Number, and may have the Idea of that Inch Line, being divisible or
not divisible, into such equal parts, as a certain number of them will
be equal to the Side-line. Now whenever he perceives, believes, or
supposes such a kind of Divisibility to agree or disagree to his Idea
of that Line, he, as it were, joins or separates those two Ideas, viz. the
Idea of that Line, and the Idea of that kind of Divisibility, and so
makes a mental Proposition, which is true or false, according as such
a kind of Divisibility, a Divisibility into such aliquot parts, does
really agree to that Line, or no. When Ideas are so put together, or
separated in the Mind, as they, or the Things they stand for do
agree, or not, that is, as I may call it, mental Truth. But Truth of
Words is something more, and that is the affirming or denying of
Words one of another, as the Ideas they stand for agree or disagree:
And this again is twofold. Either purely Verbal, and trifling, which
I shall speak of, Chap. 10. or Real and instructive; which is the Object
of that real Knowledge, which we have spoken of already.
Locke Hum IV, 5, §6, p. 576