_4. Perception of a priori[A] Principles:_ Again there are a priori principles, which the mind can perceive to be incontrovertible and of universal application, by mere reflection upon the signification of the principles and without going into the applications.[B] Such for example as that one and one make two. That two and one make three. Also, to continue the illustration above, borrowed from the late Professor Wm. James, for some time Professor of Psychology in Harvard University.--"White differs less from gray than it does from black; that when the cause begins to act the effect also commences. Such propositions hold of all possible 'ones,' of all conceivable 'whites' and 'grays' and 'causes.' The objects here are mental objects. Their relations are perceptually obvious at a glance, and no sense-verification is necessary. Moreover, once true, always true, of those same mental objects. Truth here has an 'eternal' character. If you can find a concrete thing anywhere that is 'one' or 'white' or 'gray' or an 'effect' then your principles will everlastingly apply to it. It is but a case of ascertaining the kind, and then applying the law of its kind to the particular object. You are sure to get truth if you can name the kind rightly, for your mental relations hold good of everything of that kind without exception."[C] [Footnote A: A priori, from something prior or going before, hence from antecedent to consequent; from cause to effect. See illustrations in the text quoted from James.] [Footnote B: "Truth of Thought," p. 41.] [Footnote C: "Pragmatism"--James--(1908), pp. 209, 210.]