EPITROPE

An epitrope is defined as, “a figure of rhetoric that consists in conceding something disputable, in order to lend more authority to one’ argument” (Littré, Epitrope), see concession.

Under ordinary conditions, as described by Grice’s principles, the arguer refutes everything possible, and concedes everything else. Therefore, “Peter concedes P” pragmatically implies that Peter is unable to refute P.
If the arguer concedes a doubtful proposition, he is considered a poor arguer; if he concedes something that is obviously refutable the speech is interpreted as ironic.

P is obviously wrong:
S — P, okay, but / nevertheless Q

Embedding P in a concessive structure, assigns P to the opponent, whether he  wants to endorse it.

Regarding a writer whose stylistic qualities were just discussed negatively:
I’m prepared to consider him a good stylist, but he doesn’t know what a plot is.

Irony can also arise from exaggerating the position granted:

I may have visions, but I also have some hard evidence.

See autophagy.