C’est/Ce sont vs Il/elle est

Question

This is from the lesson- c’est is used when making statements or giving opinions about something in general or nonspecific. The adjective that follows is always masculine. (Sorry, it’s in my notes so not sure if direct quote but probably is.)

Question: Is it not only always masculine but singular as well?

Eg. Tu aimes les montagnes? = You like mountains? (In general)

Would it be - Oui, c’est magnifique!

This question is not specifically in the above lessons:

My understanding is you use il/elle est or ils/elles sont with unmodified religions, nationalities or professions. Is this correct?

Il est professeur. Elles sont catholiques.

BUT if the noun is modified, then use c’est or ce sont plus an article/determiner. Is this correct?

C’est un professeur d’histoire. Ce sont mes amies françaises.

Thank you for your help!

Answer

I think you are correct in both cases.

A complication with your first question is that the French often use "la montagne" in the singular where we would use the plural - Je vais à la montagne - I am going to the mountains. But in general cases like this you could say "c'est magnifique" or, for particular mountains "elles sont magnifiques"

And for your second question, yes you have understood correctly. You can not use any modifier such as un or mes or when using il est/elle est/ils sont/elles sont. So "C'est mon ami", "c'est un professeur" etc.

In effect when you are saying "il est français", elle est professeure", ils sont catholiques" etc then français, professeur, catholique are being used as adjectives in these cases (while we might think of them as nouns in English, especially professions). So c'est un professeur (noun) or il est professeur (adjective), c'est un Éspagnol (Spaniard - noun) or il est éspagnol (adjective - Spanish).

Sorry that turned out more wordy than I intended.