Motte-and-bailey fallacy

The only reason for its existence is the desirability of the Bailey, which the combination of the Motte and ditch makes relatively easy to retain despite attack by marauders.

The Motte is the defensible but undesired position to which one retreats when hard pressed.Shackel's original impetus was to criticize what he considered duplicitous processes of argumentation in works of academics such as Michel Foucault, David Bloor, Jean-Francois Lyotard, Richard Rorty, and Berger and Luckmann, and in postmodernist discourses in general.

[5] In Shackel's original article, he argued that Michel Foucault employed "arbitrary redefinition"[2] of elementary but inherently equivocal terms such as "truth" and "power" in order to create the illusion of "giving a profound but subtle analysis of a taken-for-granted concept".

[2] Shackel labeled this type of strategic rhetorical conflation of the broad colloquial understanding of a term with a technical, artificially stipulated one as "Humpty Dumptying", in reference to an exchange in Through The Looking-Glass where that character says "When I use a word, it means just what I choose it to mean—neither more nor less.

"[2] In Shackel's description, a motte-and-bailey doctrine relies on overawing outsiders with pseudo-profundity,[2] similarly to what Daniel Dennett called a deepity.

the strategy is, as in Foucault's "Truth and power", to first make use of the word in its redefined sense, then present the redefinition as if it had already been established as the deeper content of the concept.