Necessity of pronouns in “Here is my [adjective] one” type constructs

Question

My question is about the necessity of pronouns in sentences like “This is my [adjective] one.” In English, the pronoun one is necessary for all but example #1:

1. Je vais vous montrer quelques chiens. Voici mon plus rapide.
   Let me show you some dogs. This is my fastest.
2. Je vais vous montrer quelques chiens. Voici un qui est rapide.
   Let me show you some dogs. This is a fast one.
3. J’ai deux chiens. Voici mon rapide.
   I have two dogs. This is my fast one.
4. J’ai deux grand-pères. Voici mon paternel.
   I have two grandfathers. This is my paternal one.

I made up these French sentences — are the bolded parts correct? I’m somewhat confident about the first two, but I’m not sure about #3 and #4. I know that le plus rapide is correct, but can I say le rapide to mean “the fast one”?

Answer 1

I was not sure whether this qualifies as an answer as I am not able to provide any logic to explain it but I decided to post this because my intuitions about this are very different from Begueradj's.

Je vais vous montrer quelques chiens. Voici mon plus rapide.

Sounds OK, even if “le plus rapide”, which you mentioned as well, feels more natural.

Je vais vous montrer quelques chiens. Voici un qui est rapide.

Does not sound natural, I would say “En voici un qui est rapide” instead.

J’ai deux chiens. Voici mon rapide.

That does not sound good to me. “le plus rapide”, “le plus rapide des deux”, “le plus rapide d'entre eux” or “le plus rapide de mes chiens” would all work but are obviously quite different.

J’ai deux grand-pères. Voici mon paternel.

Also sounds odd to me. I think I would simply repeat “grand-père” as in “Voici mon grand-père paternel”.

Note that both “parternel” and “rapide” have other meanings that collide with the adjectival use and might make your examples a bit confusing. “Mon paternel” means “my father” is (a somewhat old-fashioned) slang and “le rapide” was used to designate a fast train (also a bit old-fashioned).

Answer 2

1. Je vais vous montrer quelques chiens. Voici mon plus rapide.

   That is correct; but you could express that better:

   Je vais vous montrer quelques uns de mes chiens: en voici le plus rapide

2. Je vais vous montrer quelques chiens. Voici un qui est rapide.

   That is almost correct: Je vais vous montrer quelques chiens: en voici un qui est rapide.

3. J’ai deux chiens. Voici mon rapide.

   That's incorrect. Here you have the personal pronoun Je so using the possessive pronoun mon in this context is rather a bad option. I would prefer to express your idea this way:

   • J'ai deux chien: en voici le plus rapide.
   • J'ai deux chien: voici le plus rapide.

4. J’ai deux grand-pères. Voici mon paternel.

   That's incorrect. We don't say that in French. You can express your idea this way, for instance:

   • J'ai deux grand-pères: celui-ci est de mon coté paternel.
   • J'ai deux grand-pères: voici mon grand-père paternel.