How did the compound 莫 + 非 semantically shift to mean "can it be/is it possible + that"?

Question

ABC Chinese–English Comprehensive Dictionary (2003), p 628. I can't access the "slightly revised through July 2005" ed. 莫非 - Wiktionary appears correct.

1. Am I correct that 莫 here means 3 below?

1. none; nothing; not anything

2. (literary or dialectal Mandarin, dialectal Cantonese, Gan, Hakka, Min Dong) do not; don't; must not

3. particle indicating a rhetorical question

4. A surname​.

2. I don't know which meaning fits 非?

1. not be; is not; not
2. (logic) NOT
3. wrong; incorrect
4. to reproach; to blame
5. (colloquial) Used to insist on something. to have got to; to simply must

3. Still I don't understand how these two characters compound to signify "can it be that"? We're combining merely two characters that signify negation.

4. Don't we need more characters to signify the modal verb 'can', eg "possibility in either a dynamic, deontic, or epistemic sense"? Something feels missing!

Answer 1

Both 莫 and 非 denote the sense of not. The combination 莫非(a double negative) is a set phrase to mean 难道. It's often used to initiate a rhetorical question.

E. g. 莫非你不知道？ / 难道你不知道? // Don't you know it?

Answer 2

watch anime?

莫非 -> "MA SA KA"(まさか)in Japanese...

Hope this will give you both the meaning and context for your understanding.