Ignoratio Elenchi

Ignoratio elenchi (also known as irrelevant conclusion or irrelevant thesis) is the informal fallacy of presenting an argument that may in itself be valid, but does not address the issue in question. "Ignoratio elenchi" can be roughly translated by ignorance of refutation, that is, ignorance of what a refutation is; "elenchi" is from the Greek έλεγχος, meaning an argument of disproof or refutation. (Some sources give by ignorance of the issues or even by ignoring the issues as a translation of ignoratio elenchi.)

Aristotle believed that an ignoratio elenchi is a mistake made by a questioner while attempting to refute a respondent's argument. He called it an ignorance of what makes for a refutation. For Aristotle, then, ignoratio elenchi amounts to ignorance of logic. In fact, Aristotle goes so far as to say that all logical fallacies can be reduced to what he calls ignoratio elenchi.

Modern use limits this term much more narrowly to the kind of mistake described in the first paragraph above.