Domain of discourse

In a universe of discourse is understood in logic and philosophy of language, all of the items on the statements of how " are all objects ... " ( universal statement ) or " there are no items that are ... " refer (negative existential proposition ). Such statements are only useful if the meaning of " object " to a certain area, the universe of discourse is limited. Extent and type of restriction will depend on the content and the context of the statements. There is therefore not only a universe of discourse, but various discourse universes.

The English expression Universe of Discourse is also used in German- logic and computer science literature. It goes back to Augustus De Morgan ( 1847) and indicates the range of objects (in the broadest sense), about to be spoken at all.

Misunderstandings and disputes arising in logic as in everyday life often caused by people " past each other " talk of different things. Someone says, for example, that there is no winged horses. His opponent rejects this by pointing to the Pegasus. Both mentally move in different worlds. Their argument can be simple if they agree on a common universe of discourse, that is, to negotiate what is being discussed ( the discourse ) should be, if only by physically existing horses and of mythical creatures.

Also the use of negative ( complementary ) terms the universe of discourse is important. Expressions such as " non-swimmer ", " non-expert ", " non-voters " can be useful only applied to people. The non-voters together form the restricted persons entitled to vote on the universe of discourse with the voters. The limitation occurs in the use of such terms automatically. If the automatic put out of operation by means a disused chimney as Non smoking, for example, creates a pun. In general, for each term: he is associated with the negative concept combined ( more precisely, their extensions are combined ), both together constitute the universe of discourse or range of applications of the positive specific complementary concept:

In set theory, the universe of discourse corresponds to the basic amount, the amounts equivalent to those, the complements of sets of the negation of terms. In predicate logic, the universe of discourse corresponds to the area defined quantity, the object variable of a quantified statement can go through.

The Universe of Discourse is in the logic usually abbreviated as U, in the computer science with UoD.

The U is usually a subset of all existing objects and in particular in the predicate logic of fixed or presupposed in the use of object quantifiers range.