It's interesting, AmineHadji, that Arabic works this way with the copula in a nominal sentence. If it's definite, then it gets a copula هي, if indefinite, then there is no copula. The rule in Hebrew is that if both sides of the nominal sentence are nouns, then it usually gets the copula (e.g., הוא or זה). I'm just a learner in both languages, but I think that is how it works.
I was only commenting on AmineHadji's sentence. It's common in some Semitic languages to use a pronoun in nominal sentences in certain circumstances. One has to keep in mind the complication of the history of languages and also dialects (classical Hebrew or Mikra vs modern Israeli Hebrew; classical Arabic vs modern dialects and MSA). I have a grammar of classical Arabic and it indicates that pronominal use of copula is in part determined by the definiteness of the subject and predicate. Whether that continues to be the case in modern Arabic dialects is another matter that would require scrutiny of each dialect, which is WAY beyond my level of Arabic. Here is an overview that refers to optional pronoun copula: http://www.llf.cnrs.fr/sites/llf.cnrs.fr/files/evenements/colloques/DG_copula.pdf Here is a study that describes the situation in Iranian: https://halshs.archives-ouvertes.fr/halshs-01340500/document [Addendum: I'm not of much help beyond what I have here. It's interesting that languages do nominal sentences differently while there are sometimes similarities.]
Oh! Thank you! So a pronoun can act as a copula. Wow. I was modelling this lack of copula (in general) in Arabic on Russian, and since Russian doesn't use pronouns in that role, I stupidly assumed it was the same for Arabic. And of course, Arabic does have a (verb) copula in the past at least, doesn't it? I haven't met the past tense in Duolingo yet, so feel a bit nervous about thinking about it. Have a lingot.