What is the difference between "couldn't come" and "couldn't have come"?
When we compare the below two example sentences:
She couldn't come to the party.
and
She couldn't have come to the party.
Is there any difference in their nuance and meaning?
Best Answer
The two could's do not mean the same thing.
In She couldn't come, the could is an alethic modal, which refers to ability. So it means 'She was not able to come', which entails that she did not come.
In She couldn't have come, however, the could is an epistemic modal, which refers to possibility. This is Logical possibility, which is based on evidence and logical conclusions from it. Consequently, it means 'It was not possible that she came', which entails that she did not come.
Note that both readings have the same entailment; this is not uncommon.
Every modal auxiliary verb has at least two readings;
This may not be the place. This must be the place. This should be correct.
If he will agree, it's a deal. She must see him at 4pm. We should wait in that room.
She can speak ten languages, and could understand Hittite, if it were still spoken.