Conventional Implicature arise, not from the interplay or what is said with the conversational maxims, but from the conventional meanings of words that are used to say it. Grice gives the following example.
“He is an Englishman and he is brave,” which does not implicate that one follows from the other.
In the following, we will identify Grice’s notion of what is actually said with the logical form of the sentence that was uttered. To say that the two sentences cited above have the same logical form is to say that they translate to equivalent formulas in some model-theoretically logic, which in turn means that they express the same proposition.