DICTUM DE OMNI ET NULLO. This is the name of the alleged Aristotelian principle of deductive inference. There are various formulations of it. That given by Crackenthorpe is per haps as near to Aristotle's meaning as any : Quidquid affirmatur (sive negatur) universaliter de aliquo, idem affirmatur (sive nega tur) etiam de ornni de quo illud praedicatur. The more usual and concise form is, Quod de aliquo omni praedicatur, praedicatur etiam de qualibet eius parte—"What is predicated of any whole is predicated of any part of it." If "whole" be taken to mean "a kind" (or "class" in the sense of a "kind" or "type," see CLASS), then the dictum may be said to express the principle, that is, the form or spirit, of deductive inference. It is invariably treated as formulating the principle of syllogistic inference ; but this is not quite correct, as it does not apply to syllogisms composed of singu lar terms, and, on the other hand, it applies to the immediate in ference of a particular or singular proposition from a general proposition as much as to deductive syllogisms.
See H. W. B. Joseph, Introduction to Logic (1916) ; A. Wolf, Essen tials of Logic (1926) .