1. So the necklace on his desk had to be the real diamond necklace.

Question

2. So the necklace on his desk must have been the real diamond necklace.

(Does #1 mean #2? What is the difference between them?)

3. He must be strong.
4. He has to be strong.

(Are both grammatical and the same in meaning?)

Answer 1

Both 1 and 2 mean the same thing.

3 and 4 are the same in meaning, too, and are grammatically correct.

=)