In Aristotelian logic a proposition is a particular kind of sentence, one which affirms or denies a predicate of a subject, and thus asserts something true or false. Propositions fall unto three classes. Universal propositions, such as "all men are mortal" affirm or deny the predicate mortal of the "whole of" their subject, i.e. the entire class of things that the subject applies to. Particular propositionss, such as "some men are mortal" affirm or deny the predicate of only part of the subject. Singular propositions, such as "Socrates is a man" present a difficulty. Usually they were regarded as a universal proposition, since they can only be true of a single object, and thus true of all the objects (one) they possibly can be true of. On the other hand, "they are in truth the most limited kind of particular propositions".
See also: symbolic logic