A Couple of Notes About “Couple”
Couple, from the Latin word copula, meaning “bond” (yes, the term is also the origin of copulate, which is synonymous with a sense of the verb couple), has some relationship issues, so careful writers should be aware of the word’s reputation and note its proper formal usage.
Couple, as a collective noun, can be associated with a singular verb or a plural one, depending on context. But unlike other words in that class, it’s more likely to use a plural verb: “The couple is celebrating its fiftieth wedding anniversary” is just awkward, because the impersonal pronoun implies that the enduring union does not involve human beings.
But “The couple are celebrating their fiftieth wedding anniversary” strikes many readers, even those who, like me, advocate the singular they, as clumsy. So, refer to the couple as “the two” or even “they.”
Employing couple as an adjective (“Can I borrow a couple dollars?”) is common in speech but not appropriate in writing; the proper form is to treat the word as a noun followed by the preposition of preceding another noun (“Can I borrow a couple of dollars?”) When quoting a speaker in writing, silent correction — interpolating of in the record of a person’s idiomatic speech without brackets or similarly calling attention to the change — is advisable.
An exception to the “couple of dollars” preference is when the noun is a numerical reference (“I bet a couple of hundred dollars on the game”); though this is the preferred form, omission of of in this usage is still common and not considered incorrect.
However, of should remain absent from such statements as “I’ll buy a couple more batteries.”
The noun couple is also used informally to refer to more than two people. The verb form lags in generally referring to two people or things, as in connecting of train cars, though this action may repeat sequentially.
The form coupling can be a verb, an adjective, and a noun. Note, too, that “coupled with” takes a singular verb: “That incident, coupled with his behavior yesterday, is a clear sign of his instability.”