C'est v il est

Question

Is it the case that both of these sentences are grammatically correct:
- Il est mon cousin -- as a statement about a specific person

- Qui est-ce? - C'est mon cousin -- as in, He + is + my [noun]

Or, equally:

- Elle est la présidente

- C'est la présidente

If they are both grammatically correct, can you explain the difference in meaning/usage between the two versions?

My guess: can I use the top version if we are having a conversation about Paul and I then explain that Paul is my cousin: "Paul te ressemble. - Oui, il est mon cousin."
or we are having a conversation about Sophie and I then comment that she is the class president: "Sophie a l'aire très confiante. - Oui, elle a gagné l'élection et elle est maintenant la présidente."

Whereas the bottom version applies if the identity of the person is unknown:
Who is that person? C'est mon cousin.

Who is Sophie? C'est la présidente de la société.

We are still talking about a specific person, but the person is previously unknown in the conversation.
Is this correct? Would you explain it another way?

Cécile Janty-Davies · Accepted Answer

Bonjour Isabelle, 
You don't say where you saw these
This is a very difficult topic for non native French speakers, but  -
In French, the general rule is that 'il/elle est' is used WITHOUT a determiner (for professions, nationalities, religions, or adjectives), while 'c'est' is used WITH a determiner.
However, there are exceptional cases where you can use 'il/elle est' with a determiner:
1. With possessive adjectives
When referring to relationships or possession:

Il est mon frère  = He is my brother
Elle est ma meilleure amie = She is my best friend
Il est notre professeur = He is our teacher

This is the most common exception, and either 'c'est' or 'il/elle est' is perfectly acceptable in standard French.
 
2. In literary and formal style 
Occasionally in formal or literary French, you might encounter 'il/elle est' with an article: 
Elle est une femme remarquable (instead of the more common - C'est une femme remarquable)
However, this usage is quite rare, and "c'est" would be preferred in modern French.
 
3. For emphasis

C'est un artiste = neutral statement (He's an artist)
Il est artiste = describing his profession/nature
Il est UN artiste! = emphatic (He's a REAL artist! / He truly is an artist!)

Hope this helps!

Isabelle Skaburskis · Answer

Thank you, very useful!

Anne Davies · Answer

I.S. if you look at the question entitled "C’est vs il/elle est" three below yours in the French Q & A Forum, there are a couple more links to follow. Personally, I’ve fixed this in my brain by making a little mental pause after talking about a person with il/elle est. Then if the next word is an adjective, you carry on, but if it’s a noun, you usually have to rephrase using "c’est".