Two and two is

two and two is (or are ) four : As an abstract proposition or statement, is is undoubtedly correct; for four is two added to two, or twice two; but when two specific things are added to two others, the verb must be in the plural. In the former case we are saying that a certain single and definite result is attained or total given by the combination of two numbers; in the latter we say that in a given body or number of things are so many single or individual things. Two men and two are undoubtedly four; that is, four men are (constituted of) two and two. Beyond doubt, twice one is two; for it can not be that two (as a single and specific number) are twice one.