Domain of discourse

The domain of discourse is usually identified in the preliminaries, so that there is no need in the further treatment to specify each time the range of the relevant variables.

The concept, probably discovered independently by Boole in 1847, played a crucial role in his philosophy of logic especially in his principle of wholistic reference.

Alfred North Whitehead cited Augustus De Morgan as identifying "that limited class of things which is the special subject of discourse on any particular occasion.

"[3] Lewis Carroll expressed the need for a universe of discourse as follows: It sometimes happens that, in one or both of the Terms of a Proposition, the Name consists of Adjectives only, the Substantive being understood.

In order to express such a Proposition fully, we must supply the Name of some Class which may be regarded as a Genus of which each Term is a Species...The Genus referred to is called the Universe of Discourse...[4]In every discourse, whether of the mind conversing with its own thoughts, or of the individual in his folley with others, there is an assumed or expressed limit within which the subjects of its operation are confined.

Furthermore, this universe of discourse is in the strictest sense the ultimate subject of the discourse.The binary relation called set membership, expressed as