Articles for common nouns at the beginning of sentences

Question

An answer here says that "Manzanas son frutas." is ungrammatical because

Manzana is not a proper noun, so it needs the article.

However, the answer also says that

For example, both of these are correct:

Llevemos manzanas (Let's bring apples).

Llevemos las manzanas (Let's bring the apples).

They express similar but distinct ideas; the first one states that we should bring apples, but it doesn't specify which apples (maybe they still haven't bought any?). The second assumes both the speaker and the listener know of which apples they are referring to.

I am confused with the explanation here.

• If "Llevemos manzanas." is acceptable, why is "Manzanas son frutas." not acceptable?
  • Is it solely because the plural common noun manzanas is at the beginning of the sentence?
  • Is there any other exception where an article is required for a plural noun?
• Are the following true?
  • "Manzana es una fruta." is ungrammatical.
  • "Manzanas son frutas." is ungrammatical.
  • "La manzana es una fruta." is grammatical, and correctly means all apples are fruits.
  • "Las manzanas son frutas." is grammatical, and correctly means all apples are fruits.
  • "Las manzanas son las frutas." is grammatical, but looks weird (or have different meanings?).
  • "Las manzanas son unas frutas." is grammatical, but also looks weird (or have different meanings?).
  • "Una manzana es una fruta." is grammatical, but how is it different from "La manzana es una fruta."?
  • "Unas manzanas son frutas." is grammatical, but means some (but not all) apples are fruits.

Thanks!

Answer 1

Unlike in English, when used generically both count and noncount nouns take an article:

• Las manzanas son frutas.

• La manzana es una fruta.

• La salud es lo principal.

When used as an object, the article before count nouns can be dropped to mean "some" or an unspecified amount:

• Llevemos manzanas (= some apples, not all the apples in the world).

• Llevemos las manzanas (some specific apples).

"Unas manzanas son frutas" is grammatical but sounds strange. It would only be acceptable in a very restricted context where, for example, some apples are real fruit and others are toys or models. However, it would still sound strange because we would tend to use "algunas" rather than "unas":

• Algunas manzanas son frutas y otras son réplicas.

All of the following statements: "Manzana es una fruta" is ungrammatical / "Manzanas son frutas" is ungrammatical / "La manzana es una fruta" is grammatical, and correctly means all apples are fruits / "Las manzanas son frutas" is grammatical, and correctly means all apples are fruits, are true.

• "Las manzanas son las frutas" is grammatical, but looks weird. Actually, I can only think of it being used in a context where apples are mixed with other things that are not fruits, and the speaker says, for example: Las manzanas son las frutas. El resto son hortalizas.

• "Las manzanas son unas frutas" is grammatical, but also looks weird: this sentence would only work with an adjective or a relative clause, such as Las manzanas son unas frutas deliciosas / son unas frutas que crecen en todas las latitudes.

• "Una manzana es una fruta" is grammatical, but how is it different from "La manzana es una fruta": the sentence "Una manzana es una fruta" would only be applicable in the case somebody is explaining what an apple is.