How can Present Perfective and Past Perfect differ?

[Chengjiang]

Well, yes, and although I don't have a exhaustive range of experience with diverse verb systems I rather suspect languages generally won't have a dedicated present perfective for this narrow range of purposes. zompist is correct in saying that technically there are exceptions to the "no semantic present perfectives" principle I stated above.

I remarked this because Russian does have what is formally a perfective present tense, which it also uses for gnomic purposes, as in proverbs (as I said before, its main use is as a future tense). So I think the fact that Russian could use the perfective present for such uses but doesn't is significant.

Yes. It's morphologically present (or non-past) perfective, but it's clearly not treated as having a present perfective meaning.

[hwhatting]

Yes. It's morphologically present (or non-past) perfective, but it's clearly not treated as having a present perfective meaning.

Gnomic uses don't count for you?

[Chengjiang]

Yes. It's morphologically present (or non-past) perfective, but it's clearly not treated as having a present perfective meaning.

Gnomic uses don't count for you?

Er, sorry, that was a mistake. Looking back it seems like I missed that part of what you were saying and just noticed the bit about it not being used for performative or narrative purposes.