Learn English – Does ‘each other’ function as singular or plural

grammatical-numberverb-agreement

Are either of the following sentences grammatically correct?

We know what each other are doing

and

We know what each other is doing

Neither of them sounds right to me, but surely one of them must be, depending on whether 'each other' functions as a singular or plural? Of course there are workarounds like "Each of us knows what the other is doing", but is it possible to keep the words "each other" together in such a sentence?

Best Answer

If you notice that each other, while idiomatic, is not unbreakable, it begins to come clear.

The reciprocal phrase each other can be separated into one determiner binding something in the subject (each, each one), and one determiner binding something in the object (other, the other), viz:

  • Each (one) of us knows what the other (one (of us)) is doing. (dual)
  • Each (one) of us knows what the others/other ones are doing. (plural)

And some of these quantifiers may be floated to pre-verbal position:

  • We each know what the other (one) is doing. (dual)
  • We each know what the others/other ones are doing. (plural)

From this it's easy to see how each and other hook up:

  • Each of us knows the other.
  • We each know the other.
  • We know each other.

But that doesn't resolve the number problem that comes from having two determiners potentially conflicting. So both

  • *We know what each other is doing. and
  • *We know what each other are doing.

feel wrong.

Of course, there are other quantifiers that specify more precisely,
especially when they're separated, viz:

  • We both know what the other is doing. (dual)
  • We all know what the others are doing. (plural)
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