Are the cats and dogs of the idiom "it's raining cats and dogs" plural in usage?

Question

I recently heard someone say the following:

It's cats and dogs out there!

As in "it's raining cats and dogs out there." I then thought that person should have said

Those are cats and dogs out there!

because the phrase refers to multiple objects. My hobbyist-linguist friend then said to me that the person was correct because cats and dogs were a compound subject - a result of the idiom itself. I'm inclined to believe my friend, but I'm not sure. I think I may have initially been confused because of the diversion from the format of use of the idiom.

Which is correct?

Answer 1

The use of any plural noun as an adjective, adverb, adjective clause, or adverbial clause does not affect the count of the verb. The verb only cares about the subject of the sentence.

What is the subject of this particular sentence? If it were "cats and dogs", then you would be correct to believe the sentence would be "there are cats and dogs" or something similar. However, the actual subject of the sentence is the expletive pronoun "it" (sometimes, and with great protest from "it", referred to as a "dummy" pronoun).

It is unfortunate.

In this case, "it" is always a singular subject for the purposes of the verb. There is no actual subject matter with an expletive pronoun. A subject can be devised and a sentence reworded, but

it is not necessary to do so...

Answer 2

The idiom can be considered both (1) to be extra-grammatical (here hijacking a reasonably common if far from simple sentence structure and using it in a strange way) and (2) to be using words in a strange way.

We'd expect a weather-it sentence to have one or more adverbs or prepositional phrases etc modifying the verb:

• It's raining continuously. / It's snowing really heavily out there.
• It's snowing for the first time in two years. / It's thundering on the coast of Maine.

But here, we have a noun group, cats and dogs, obviously used adverbially rather than as a plausible direct object.

• It's raining cats and dogs [out there].

With a typical extraposed-it sentence

• It's clear that the MP doesn't know the true facts.

a rearrangement fronting the semantic subject is possible (if unwieldy):

• That the MP doesn't know the true facts is clear.

As there is no semantic subject with weather-it sentences, this is impossible with say It's raining.

But at first glance,

• Cats and dogs are being rained out there.

looks a possibility (after all,

• Cats and dogs are being trained out there.

is fine).

But it's ungrammatical. The idiom (as idioms usually do) resists such transformations.

And that really includes, in standard English, deleting the verb.

The Farlex Partner Idioms Dictionary does admittedly give a parallel example (which may well have encouraged OP's example):

Wear a hat – it's brass monkeys out there tonight!

But it adds the caveats [usually British] slang.

So 'It's raining cats and dogs' is best regarded as an idiom best analysed at the idiom level, with 'cats and dogs' only in this usage a very strange adverbial looking like a noun phrase, and 'It's cats and dogs out there' a non-standard adaptation apparently using 'cats and dogs' adjectivally (so doubly resistant to analysis about 'plurality') but with 'Those are cats and dogs out there' not even vaguely acceptable in the intended sense.

Answer 3

Grammatically, "It is raining cats and dogs" makes the verb "rain" transitive. In fact, the verb "rain" is intransitive. In this respect, this archaic idiom is grammatically wrong, from the viewpoint of present day grammar. I think we ought to avoid using this grammatically anomalous expression. You can simply say "It's pouring rain out there." --- Henry 2022-06-11