The Commens Dictionary
Quote from ‘Multitude and Number’
In all discourse, or reasoning, there are virtually two parties. Either there are actually two parties, as when one speaker addresses an audience of one or more persons; or else one person reasons out something with himself, and even then, the difference between his conceptions and opinions before and after a given operation of thought results in his influencing himself much as one person influences another; so that we may say that even in this case there are virtually two parties.
The discourse of these two parties must relate to something which is common to the experience of both, or else they will be quite at cross-purposes. This common experience considered as a collective whole of units, the logicians for the last half century [have] commonly called the universe of discourse.