18.  Recapitulation.

Wherever we perceive the agreement or disagreement of any of our ideas, there is certain knowledge:  and wherever we are sure those ideas agree with the reality of things, there is certain real knowledge.  Of which agreement of our ideas with the reality of things, having here given the marks, I think, I have shown wherein it is that certainty, real certainty, consists.  Which, whatever it was to others, was, I confess, to me heretofore, one of those desiderata which I found great want of.

CHAPTER V. OF TRUTH IN GENERAL.

1.  What Truth is.

What is truth? was an inquiry many ages since; and it being that which all mankind either do, or pretend to search after, it cannot but be worth our while carefully to examine wherein it consists; and so acquaint ourselves with the nature of it, as to observe how the mind distinguishes it from falsehood.

2.  A right joining or separating of signs, i.e. either Ideas or Words.

Truth, then, seems to me, in the proper import of the word, to signify nothing but the joining or SEPERATING of signs, as the things signified by them do agree or disagree one with another.  The joining or separating of signs here meant, is what by another name we call proposition.  So that truth properly belongs only to propositions:  whereof there are two sorts, viz. mental and verbal; as there are two sorts of signs commonly made use of, viz. ideas and words.

3.  Which make mental or verbal Propositions.

To form a clear notion of truth, it is very necessary to consider truth of thought, and truth of words, distinctly one from another:  but yet it is very difficult to treat of them asunder.  Because it is unavoidable, in treating of mental propositions, to make use of words:  and then the instances given of mental propositions cease immediately to be barely mental, and become verbal.  For a mental proposition being nothing but a bare consideration of the ideas, as they are in our minds, stripped of names, they lose the nature of purely mental propositions as soon as they are put into words.

4.  Mental Propositions are very hard to be treated of.

And that which makes it yet harder to treat of mental and verbal propositions separately is, that most men, if not all, in their thinking and reasonings within themselves, make use of words instead of ideas; at least when the subject of their meditation contains in it complex ideas.  Which is a great evidence of the imperfection and uncertainty of our ideas of that kind, and may, if attentively made use of, serve for a mark to show us what are those things we have clear and perfect established ideas of, and what not.