should have done - what is the name of this grammatical structure?

iasadih It occurred to me yesterday that I have forgotten what it is called. Something with "perfect", I guess.

'(should) have done' is present perfect tense.
'He should have done it earlier.'

No other name for the above?

So what in Past is :
It could happen.

in Present Perfect is:
It could have happened.

Right?

Strange, how a change of the tense turns the meaning upside down, so to speak.

iasadih It occurred to me yesterday that I have forgotten what it is called. Something with "perfect", I guess.

This sentence is semantically incorrect becasue we can't use past time marker with present perfect tense.

Is that a semantic mistake? I associate semantics with meaning and grammar with the choice of tense.

Indeed, present perfect does not mix with past, generally.

Seem inconsequent, because it is correct to say "I said I am not going", where past is abandoned for general presence.

Presumably, you would suggest "It occurred to me I had forgotten".

iasadihSo what in Past is :It could happen.

That is not past; that is conditional present: It could happen today or tomorrow if we careless.
'Could have happened' is past conditional: I could have happened yesterday if we had been careless.

I guess there are two layers - of type of structure and function.

It could happen means different things depending on the rest of the sentence, or the context.

1. hypothetical present/future (I mean time reference)
If they both were in Warsaw today/tomorrow, they could meet. But they are not, so they can't.

2. open past
If they both were in Warsaw at that time, t

I call could have, must have, will have, ... (with a past participle) "modal perfect" tenses, and the plain could, must, will, ... (with a bare infinitive) "modal" tenses. Strictly speaking, I suppose they aren't really tenses.

I have also heard could have, must have, will have, ... (with a past participle) called "a modal verb with a perfect infinitive without to

Based on your last post, it seems to me that you have run into the "confused" state most learners have experienced at some point of the learning process.

iasadih It occurred to me yesterday that I have forgotten what it is called. Something with "perfect", I guess.

This senten

grammarfreakiasadih It occurred to me yesterday that I have forgotten what it is called. Something with "perfect", I guess.This sentence is semantically incorrect becasue we can't use past time marker with present perfect tense.

That sentence is fine.! A thought occurred to me yesterday. The thought was 'I have forgotten what it was called'."

The spea

Looks like we have two threads now

@fivejedjohn
Can you support this exlanation with a quotation of some trustworthy o