Nouns which are masculine when singular and feminine when plural

Question

If you look at the following chart:

chaude amour

You'll find that between 'chauds amours' and 'chaudes amours' the former does not even exist. In the singular there is some debate between 'chaude amour' and 'chaud amour', but in the long course of history usually 'chaud amour' predominates though 'chaude amour', for example, in the early 2000s was more common. In the dictionary it says here:

,,Amour, après avoir longtemps hésité entre les deux genres, est considéré par les grammaires classiques comme masculin au singulier et féminin au pluriel. Le genre masculin semble aujourd'hui se généraliser pour les deux nombres`` (cf. aussi Littré, rem. et Grev. 1964, § 253)

I mentioned this to my language exchange partner and she was not aware of it though she admitted that she never says 'chauds amours'. She was dismissive of the rule as a useless detail. My question is are French speakers aware of this? Are they aware that some nouns (I think there are a few more) switch genders as they switch number? If I were to say 'chauds amour' would that leap out at them in the same way that "I require that he remains in the park" leaps out to English speakers? So far I've never met an monolingual English speaker that understands why the sentence "I require that he remains in the park" is ungrammatical?

Answer 1

Most French speakers don't know

There are, as far as I know, three nouns in total that switch from masculine in the singular to feminine in the plural: amour (love), délice (delight) and orgue (organ, the musical instrument).

In French noun genders tend to be more visible in singular than in plural as for a plural form it can only be seen through the agreement of an adjective:

Des voitures (some cars) : feminine

Des camions (some trucks) : masculine

Des voitures garées (some parked cars)

Des camions garés (some parked trucks)

Even in this example, you can see that the agreement of the adjective only matters in the written form. It is silent otherwise.

Now, you can combine this with the relative rarity of the plural form of these three nouns to see why most people never ran into a situation where this factoid mattered the slightest.

Now on this very website you are going to see a bias as people here are way more interested in grammatical peculiarities that the average Joe but we need to admit that is still a niche center of interest.

I think you could make a nice trivia question about this!

Answer 2

It's mostly unknown, except in literature, poetry and songwriting.

The reason is, it's pretty rare to use "amours" in plural form in speech, even more with an adjective that sounds different when it's feminine. Even if everyone used it correctly, it would be hard to pick up the rule by listening alone. In my opinion that's why that rule is not very known and rarely applied.