Grice's Oxford lectures on implicature

Speranza

While Sidonius had spoken of 'inplicatura' [sic] in one letter to a friend (vide my "Loeb is all you need"), Grice made the anglican expression 'implicature,' pretty common.

In "Causal Theory of Perception," he notes that examples like

A: Where is your wife?
B: Either in the garden or the kitchen.

and

A: Is he doing well at Collections?
B: He has beautiful handwriting.

should count as 'conversational implicatures' (Note in Grice, "Way of Words"). But he did not use the word THEN.

By 1965 he WAS using 'conversational implicature'.

Oddly, and fortunately, he wasn't yet wedded to a Kantian square of categories: 'quantitas,' 'qualitas,' 'relatio,' and 'modus'. Rather, he spoke of two desiderata and two principles.

Mainly they are

The desideratum of conversational clarity.
The desideratum of conversational candour.
The principle of conversational self-love
The principle of conversational benevolence.

Genius!