Moral certitude is that with which judgments are formed concerning human character and conduct; for the laws of human nature are not quite universal, but subject to occasional exceptions. It is moral certitude which we generally attain in the conduct of life, concerning, for example, the friendship of others, the fidelity of a wife or a husband, the form of government under which we live, or the occurrence of certain historical events, such as the Protestant Reformation or the French Revolution. Though almost any detail in these events may be made a subject of dispute, especially when we enter the region of motives and try to trace cause and effect, and though almost any one of the witnesses may be shown to have made some mistake or misrepresentation, yet the occurrence of the events, taken in the mass, is certain.

Father John Rickaby (First Principles of Knowledge) observes that certitude is not necessarily exclusive of all misgiving whatsoever (such as the thought of the bare possibility that we may be mistaken, for we are not infallible), but of all solid, reasonable misgivings. The term moral certitude is used by some philosophers in a wider sense, to include an assent in matters of conduct, given not on purely intellectual grounds of evidence, but through the virtue of prudence and the influence of the will over the intellect, because we judge that doubt would not be wise. In such a case, we know that an opinion or a course of action would be right as a rule, let us say, in nine cases out of ten, though we cannot shut our eyes to the possibility that the particular case which we are considering may be the exceptional case in which such a judgment would be wrong. Other philosophers say that in such a case we are not certain, but only judge it wise to act as if we were certain, and put doubts aside because useless. But it seems clear that in such a case we are certain of something, whether that something be described as the truth of a proposition or the wisdom of a course of action. This certitude might perhaps better be called Practical certitude, since it mainly concerns action. Hence, it is said that in cases in which it is necessary to act, in which great issues are involved, and yet the evidence, when logically set forth, would seem to amount to no more than a higher probability for one course than for another, the standard of judgment, or criterion, is the judicium prudentis viri, the judgment of a wise man, whose mind is unclouded by passion or prejudice, and who has some knowledge derived from experience of similar cases. Such a judgment is totally different from the spirit of the gambler's throw, which is reckless not only of certainty but even of probability.