“The criterion of certitude is the sign by which certitude is perfectly distinguished from error” (p. 52). We remark, that there are criteria of truth, but not properly of certitude. Certitude is the firm adhesion of the mind to the truth made known to it, and needs no criterion, because it certifies itself by its very existence. The author says that “certitude is at the same time a state and an act of the mind. As a state, it may be defined to be a disposition by which the mind tends to adhere firmly to the known truth” (p. 50). But this is a great mistake. First, the _act_ of adhering to truth is an act of judging, not an act of certitude. Secondly, the _state_ of certitude is not a disposition by which the mind tends to adhere to truth. So long as the mind tends to adhere, there is no adhesion, and therefore no certitude. Certitude is the rest of the mind in the known truth. “Reason is a perception” (p. 62). It is superfluous to remark that reason is a faculty, and no perception is a faculty. “Consciousness cannot be deceived, although it may deceive” (p. 62). How can consciousness deceive? And if it can deceive, on what ground does the author immediately add: “Hence consciousness gives true certitude”? “The evidence of senses is that invincible propensity which induces us to refer our sensations to the bodies which, according to our conviction, have been the cause of them” (p. 63). We observe, that our propensity cannot be our evidence. Our evidence must be objective, whilst our propensity is a subjective disposition. The evidence of senses is the evident perception of an object acting on the senses. The invincible propensity is nothing but the necessity of yielding to that evidence.