Bach on Grice on "therefore"

From online essay by Bach, "The myth of conventional implicature"

Bach writes:

"Grice makes a similar point about ‘therefore’."

Bach quotes from WoW:

Grice:

"If I say (smugly), He is an Englishman; he is, therefore, brave, I have certainly committed myself, by virtue of the meaning of my words, to its being the case that his being brave is a consequence of (follows from) his being an Englishman. But while I have said that he is an Englishman, and said that he is brave, I do not want to say that I have said (in the favored sense) that it follows from his being an Englishman that he is brave, though I have certainly indicated, and so implicated, that this is so. I do not want to say that my utterance of this sentence would be, strictly speaking, false should the consequence in question fail to hold. (Grice 1989, p. 25)

---

Bach comments:

"‘Therefore’ is not the most convincing example, for
it seems that the truth of the utterance does require
that the second proposition be a consequence
of the first. More plausible is Grice’s earlier example involving ‘but’,
[She is poor but she is honest] where the putative contrast between being poor and being honest is, he claims, “implied as distinct from being stated” (Grice 1961, p. 127)."

Ah well. I'd need to analyse Bach's 'seem'

"it seems that the truth of the utterance DOES
require..."

It strikes me as lovely that "it seems ..." is all doubt, but the emphatic "does" (in "the utterance does require") is all about NO doubt!

So, this may be idiosyncratic to Bach's use?