(b) Judgments are physically certain, when error is impossible according to the laws of nature, the opposite of what is held by the mind being unrealizable except through intervention of another cause. Example: The judgments that he who takes poison will destroy life, that he who applies fire to a house will destroy property, are physically certain. because natural agencies, like poison and fire, act infallibly when applied to suitable matters and under suitable conditions and left to their course, unless they are overruled by superior power. (c) Judgments are morally certain, when error is impossible according to what is customary among mankind, the opposite of what is held by the mind being so unlikely that it would be imprudent to be moved by it. Examples: One is morally certain that what a reputedly truthful and competent person relates to one is true. A person is morally certain that a conclusion he has drawn about his duty in a particular instance is correct, if he believes that he has overlooked no means of reaching the truth. Testimony and inference, since they come from free and fallible agencies, may lead into error; but, when they appear to have the requisite qualities indicative of truth, they are for the most part reliable and in practical life have to be considered as such. 644. As to the certainty that is required in the judgment of conscience, the following points must be noted: (a) Metaphysical certainty is not required, since conscience does not deal with primary propositions, but with deductions about particular acts. The first moral principles, which are the object of synderesis, and at least some of the general conclusions, which are the object of moral science, are metaphysically certain (see above 145, 300), as they are based on necessary relations; but the particular conclusions, which are the object of conscience, are concerned with the contingent and the individual. (b) Physical certainty is not required for the judgment of conscience, since conscience is not concerned with the activities of natural agents, but with the activities of moral agents that act with freedom and responsibility. (c) Moral certitude, therefore, is sufficient for the conclusions drawn by conscience. That a higher kind of certitude is not necessary should not surprise us, for it would be unreasonable to expect that the same degree of assent be given to judgments that are concerned with particular and contingent cases as to those that are concerned with universal and necessary principles.