Let us put aside the word “infallibility;” let us understand by certitude, as I have explained it, nothing more than a relation of the mind towards given propositions:—still, it may be urged, it involves a sense of security and of repose, at least as regards these in particular. Now how can this security be mine,—without which certitude is not,—if I know, as I know too well, that before now I have thought myself certain, when I was certain after all of an untruth? Is not the very possibility of certitude lost to me for ever by that one mistake? What happened once, may happen again. All my certitudes before and after are henceforth destroyed by the introduction of a reasonable doubt, underlying them all. _Ipso facto_ they cease to be certitudes,—they come short of unconditional assents by the measure of that counterfeit assurance. They are nothing more to me than opinions or anticipations, judgments on the verisimilitude of intellectual views, not the possession and enjoyment of truths. And who has not thus been balked by false certitudes a hundred times in the course of his experience? and how can certitude have a legitimate place in our mental constitution, when it thus manifestly ministers to error and to scepticism? This is what may be objected, and it is not, as I think, difficult to answer. Certainly, the experience of mistakes in the assents which we have made are to the prejudice of subsequent ones. There is an antecedent difficulty in our allowing ourselves to be certain of something to-day, if yesterday we had to give up our belief of something else, of which we had up to that time professed ourselves to be certain. This is true; but antecedent objections to an act are not sufficient of themselves to prohibit its exercise; they may demand of us an increased circumspection before committing ourselves to it, but may be met with reasons more than sufficient to overcome them.