Presupposition

A presupposition is anything that a native speaker of a language knows is part of the meaning of a sequence of that language,  even if it doesn't appear on the surface of the sequence .

Example of a Pressuposition in the context of a Verbal Attack: Consider the sentence,
 * EVen JOHN could close THAT deal! (Capital letters emphasize intonation and focus of speaker).

Can you hear the presupposition? As a native speaker of English, you know that sentence presupposes 2 additional sentences, neither of which appears anywhere on the surface: People that are not fluent speakers of English are unaware that the sentence is insulting to both John and the deal in question. How could they know? I repeat - because this is one of those situations where people are "too close to the forest to see the trees" - there is not one single negative word about either John or the deal in question. Nevertheless, because you are a native speaker you hear those negative presuppositions loud and clear.
 * 1) The deal doesn't amount to much
 * 2) John doesn't amount to much, either

(Copied from Chapter 6 of Success with the Gentle Art of Verbal Self-Defense)

Related:
 * Verbal Abuse
 * Verbal Self Defense