‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ I have one step farther to make:—let the proposition to which the assent is given be as absolutely true as the reflex act pronounces it to be, that is, objectively true as well as subjectively:—then the assent may be called a _perception_, the conviction a _certitude_, the proposition or truth a _certainty_, or thing known, or a matter of _knowledge_, and to assent to it is to _know_. Of course, in thus speaking, I open the all-important question, what is truth, and what apparent truth? what is genuine knowledge, and what is its counterfeit? what are the tests for discriminating certitude from mere persuasion or delusion? Whatever a man holds to be true, he will say he holds for certain; and for the present I must allow him in his assumption, hoping in one way or another, as I proceed, to lessen the difficulties which lie in the way of calling him to account for so doing. And I have the less scruple in taking this course, as believing that, among fairly prudent and circumspect men, there are far fewer instances of false certitude than at first sight might be supposed. Men are often doubtful about propositions which are really true; they are not commonly certain of such as are simply false. What they judge to be a certainty is in matter of fact for the most part a truth. Not that there is not a great deal of rash talking even among the educated portion of the community, and many a man makes professions of certitude, for which he has no warrant; but that such off-hand, confident language is no token how these persons will express themselves when brought to book. No one will with justice consider himself certain of any matter, unless he has sufficient reasons for so considering; and it is rare that what is not true should be so free from every circumstance and token of falsity as to create no suspicion in his mind to its disadvantage, no reason for suspense of judgment. However, I shall have to remark on this difficulty by and by; here I will mention two conditions of certitude, in close connexion with that necessary preliminary of investigation and proof of which I have been speaking, which will throw some light upon it. The one, which is _à priori_, or from the nature of the case, will tell us what is not certitude; the other, which is _à posteriori_, or from experience, will tell us in a measure what certitude is. 1. Certitude, as I have said, is the perception of a truth with the perception that it is a truth, or the consciousness of knowing, as expressed in the phrase, “I know that I know,” or “I know that I know that I know,”—or simply “I know;” for one reflex assertion of the mind about self sums up the series of self-consciousnesses without the need of any actual evolution of them.