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?
Best Answer
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).
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