Full Idea
Gricean theories of metaphor …assume that conversational implicatures are generated via literal contents, and hence that a sentence cannot generate an implicature without being literally meaningful.
Gist of Idea
Gricean theories of metaphor involve conversational implicatures based on literal meanings
Source
Ofra Magidor (Category Mistakes [2013], 3.5)
Book Reference
Magidor,Ofra: 'Category Mistakes' [OUP 2013], p.72
A Reaction
Magidor gives not details of such theories, but presumably the metaphor is all in the speaker's intention, which is parasitic on the wayward literal meaning, as in cases of irony.