'il' vs. 'ce' in referring to an event or idea

Question

What are the general rules on deciding between il and ce for referring to an idea in the form of a proposition or other gender-less form (such as an infinitive)?

Examples in English would include:

(a) Is he? That is the question.
(b) Is he? It's hard to tell.
(c) It's hard to know what to think.

What I intended was that in (a) and (b) the pronoun should follow the idea it refers to, but in (c) precede. In (a) the idea is assigned to a class, but in (b) only described. Maybe in (c), the pronoun is expletive and does not refer at all.

Whenever I could use either ce or il please tell me so and what the difference may be. If some third pronoun works better or as well, please also tell me.

This request may be rather indefinite, but if I am obviously overlooking some important factor affecting the choice please let me know using example sentences. Thank you.

Answer 1

• (a) Is he? That is the question.

Casual:

Est-ce qu'il l'est ? C'est la question.

Literary:

L'est-il ? Telle est la question.

Note that:

Elle est la question. is impossible.

• (b) Is he? It's hard to tell.

Spoken French:

C'est dur à dire.

Difficile à dire.

Formal, written French:

Il n'est pas facile de le dire/ de le déterminer.

• (c) It's hard to know what to think.

Casual, spoken French:

C'est difficile de savoir ce qu'il faut penser.

Formal, written French:

Il est difficile de savoir quoi penser.

Answer 2

Well, 'il' directly refers to the person/object concerned, it includes the subject within it, while 'ce' needs the subject to be assigned right after. Ce chien est grand = il est grand ; Cette fille est jolie = elle est jolie ; Cette idée est bonne = elle est bonne (this idea is good = it is good) Does that help you ? :/

Answer 3

I don't have the reputation to comment, but there's a spelling mistake in Jlliagre's answer. It should be "L'est-il?" not "L'est-t-il?"