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 interpretation or 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.