"je suis un artist"??
Ne devrait-il pas être "je suis artist"?
Both are correct but the sense is different.
1) Je suis artiste = your Job / work / profession / it is the answer at the question "what is your job ?"
2) Je suis un artiste = what you are
So with the 1st proposition the adjectives you can add will be in related with the job. (professionnel, confirmé,...)
So with the 2nd proposition the adjectives you can add will be in related with you. (beau, fort, musclé....)
Well, I want to follow up on AminA44938's question. Can you say je suis un medecin? Because I can see myself saying "Deep down inside, I'm an artist," but I can't say "deep down inside, I'm a doctor." Maybe "deep down inside, I'm a caring person" but not "un medecin."
This means we definitely shouldn't say "je suis un assistant réceptionniste", oui?
Well, you could always say Je suis un médecin/professeur/artiste..., but it depends on the case you speaking about.
For instance, with artiste, it's also an adjective. Thus, in Je suis un artiste, artiste is considered an adjective. As you said, you could say Deep down inside, I'm an artist = Au fond de moi, je suis un artiste.
When it's not an adjective, it can also mean that it's a role. For instance, actors of Grey's Anatomy could say In the show, I am a doctor = Dans la série, je suis un médecin. Or a mother can say With my children, I have to be a nurse, a teacher, a psychologist... = Avec mes enfants, je dois être une infirmière, une professeur, une psychologue...
And of course, when it's modified by an adjective or an adjective phrase. For instance I am a very competent doctor = Je suis un médecin très compétent or I am a doctor who doesn't fear authority = Je suis un médecin qui n'a pas peur de l'autorité
Your follow-up helped me better grasp this whole thing. To answer your question, you can't say "je suis un medecin" as it doesn't make sense. Medecin is a profession, you can't BE a profession by nature.
"Je suis un artist", on the other hand, goes along the lines: "I am emotional, I have feelings, I am artistic, I speak art, art flows through me, I have artistic traits". As you can see, the mood here is casual.
I am an artist by nature. That's who I am.