"This is new."
Please take a look at this: http://www.frenchtoday.com/blog/cest-versus-il-elle-est
After reading the page I proposed, I thought you would have understood that the rule applies ONLY if a NOUN preceded by a determiner follows verb the être at 3rd person, not an adjective:
He is new, she is new, they are new = il est nouveau, elle est nouvelle, ils sont nouveaux or elles sont nouvelles.
He is a new man, she is a new woman, they are new men, they are new women: c'est un homme nouveau, c'est une femme nouvelle, ce sont des hommes nouveaux, ce sont des femmes nouvelles.
This is new, that is new, these are new, those are new = c'est nouveau, ceci est nouveau, cela est nouveau, ceux-ci sont nouveaux, celles-ci sont nouvelles, ceux-là sont nouveaux, celles-là sont nouvelles.
"nouveau, nouvel, nouvelle, nouveaux, nouvelles" is subjective and relative, since it means "new to me". It is placed before the noun.
- c'est ma nouvelle jupe (it can be second-hand or you may have bought it some time ago)
"neuf, neuve, neufs, neuves" is objective and factual, since it means "brand new". It is placed after the noun.
- c'est ma jupe neuve (I just bought it from a store)
If you tell us what exactly you do not understand, we can try to give you simple explanations.
However, grammar is essential in French and the basic notions of grammar are very similar to English ones. In other words, you have to understand your own language to learn another one.
Have you seen this? https://www.duolingo.com/comment/4614759
I have read the article Sitesurf has posted here (Android app does not reply to comments) but one doubt still remains. As an example, the author talks about "la mer": "La mer est bleue. Elle est verte. Elle est violette. Elle est noire.". Why do these sentences with "elle" are considered "elle est + adj" and not "c'est + category"? If she is talking about the sea in general, these sentences should be the same as "C'est toujours beau, la mer", no?
Since all nouns are gendered, you can use the personal pronouns as you would use "it" in English.
"Elle est belle" is the correct way of using the personal pronoun "elle" to represent "la mer" (as it would represent "la femme" or "la robe").
"La mer" in general or "la mer" as a specific one here does not alter the use of a personal pronoun.
"C'est beau, la mer" is informal French, emphatic with a double subject and does indeed refer to "la mer en général".
When there is no context pointing to a generality, the description of "la mer" will be specific and can take the form of "elle est belle, la mer", with a similar construction.
When the English sentence just has "it is + adjective", you don't know if "it" refers to a situation or an object or an animal. So, Duolingo gives the French personal pronouns as best translations and adds "c'est" if the sentence still makes sense as a comment on a situation.
Okay, I believe I misunderstood the article a little bit. But can I use "elle" and a feminine adjective to talk about a general noun? And then I only use c'est + masc. adj. to make comments about a situation? The problem to me is specifically the use of c'est + masc. adj. with a feminine noun attached to it, e.g. "C'est toujours beau, la mer". I can understand if you look at the sea and say "C'est beau" because you are not talking precisely about anything, but about the situation, but "C'est toujours beau, la mer" does not seem to fit into this idea...
C'est beau followed by a feminine noun is only a grammatical constraint, which is the fact that c' is always masculine. So the masculine "beau" combined with "la mer" may sound odd, but it can happen in other cases as well.
For instance: "cet homme est la victime": "une victime" remains a feminine noun, whomever it can represent.
Same story with: "cette femme est le témoin".
"C'est fou, cette situation !" isn't it?
I think I understand it... Hahaha. It is often used like we would use in Portuguese (my native language), so "cet homme est la victime", for example, is quite easy for me. My only difficulty is with sentences like "C'est fou, cette situation !" (indeed it is...), but I believe I can manage to continue my studies statisfied with your explanation now hahaha. It also works similarly to Portuguese, but we would rarely use the feminine noun after the comment, only if asked what we were referring to. (therefore, it wouldn't be in the same sentence, so as to avoid the masculine adjetive / feminine noun conflict).
Thank you very much for your answers and patience!