Universe of Discourse: In
logic, all of the things one's
arguments are about, and no others.
There always is some Universe of Discourse, even if it is wholly
unspecified and tacit, but sometimes making explicit what is the
Universe of Discourse prevents fallacies or unclarities. For example,
when one is discoursing about numbers, it makes little sense to consider
persons, and when one is discoursing about mythical or possibly
mythical entities it is well to lay this down clearly.
How the Universe of Discourse is dealt with, if at all, depends much
on the type of logical argumentation one is involved with, and on one's
clarity of mind. In mathematical logic, the domain of
model is the standard Universe of Discourse.
It should be noted that by restricting or extending one's Universe of
Discourse one may alter the truth-values of one's
statements about it.