Usage of Not

[Justin_Huang]

1. Not all horses are black.
2. It is not that all horses are black.
3. It is not correct to say that all horses are black.

Is there any slight difference among these sentences?

[Dozy]

#1 is a plain statement of fact. #3 may be just a more verbose version of #1, or it may be contradicting something said.

#2 has a different flavour from the other two. It presupposes a context in which people might be expecting the fact that all horses are black to be some kind of explanation or reason for something.

[Justin_Huang]

Thank you so much, Dozy.
Now I understand well.