ABSTRACT
Sometimes, in a language such as English, there are special words or phrases which serve to indicate a particular universe of discourse. Words such as ‘everyone’, ‘someone’ and ‘no one’ commonly make it clear that the universe of discourse is human beings. The most usual way of specifying a class which is to be our universe of discourse is by means of some descriptive word or phrase; e.g. ‘human beings’, ‘integers’, ‘animals’, ‘citizens of Canada’ and so forth. A class which has no members, such as (presumably) the class of unicorns, is said to be an empty class, and one which has members – however many or however few – is said to be a non-empty class. So when such classes form our universes of discourse, we speak of empty and non-empty universes of discourse respectively. We refer to those universes of discourse which have no members at all, i.e. to empty universes of discourse.
