Full Idea
Grice's maxim of quality says one ought not to assert what one believes to be false.
Gist of Idea
Grice's maxim of quality says do not assert what you believe to be false
Source
report of H. Paul Grice (Some Models for Implicature [1967]) by Ofra Magidor - Category Mistakes 5.2
Book Reference
Magidor,Ofra: 'Category Mistakes' [OUP 2013], p.112
A Reaction
The obvious exception is irony, where are truth is asserted, but the listener is supposed to spot that you are not really asserting it.