There are still sticklers among us who see a distinct difference between each other and one another. They use each other when discussing two people or things, and one another when discussing more than two people or things.

According to this system, the following sentences would both be correct: The twins told each other everything and The triplets told one another everything. But The twins told one another everything and The triplets told each other everything would both be incorrect.

This rule has been around since the eighteenth century. Yet it is routinely ignored by just about everyone, including our finest writers. Nowadays, virtually no one even knows it exists.

Taken literally, the phrase each other does seem limited to two entities only, represented by the singular pronoun each and the singular pronoun other.

The twins told each other everything means that each twin told the other twin everything. So far, so good. But The triplets told each other everything means that each triplet told the “other” triplet everything—which makes no sense because there are two other triplets.

So instead the sticklers demand The triplets told one another everything. To them, other means “one of two” and another means “one of more than two.” By this reasoning, one another refers to a group of three or more whose members include one and another.

The sticklers reject The twins told one another everything because it means that one twin told “another twin” everything. To the sticklers, “another twin” means the impossible: three (or more) twins.

The trouble with the rule is that each other and one another were already long-established idioms in the eighteenth century, and many idioms fall apart under this sort of tortured scrutiny—try analyzing as it were or by and large sometime.

Whether some people like it or not, each other and one another are synonyms. So let’s move on.

The possessive of each other is each other’s, never each others’. Although a lot of neophytes write each others’, the authorities agree unanimously that each other’s is the only acceptable option. Same with one another’s.

A thorny problem with each other’s and one another’s is illustrated in the sentence that follows. Should we say The lawyer and the banker admired each other’s car or admired each other’s cars?

The traditionalists are at odds here. In The Careful Writer Theodore M. Bernstein claims that each other’s is equivalent to their. So Bernstein would say admired each other’s cars. But Bryan A. Garner leans toward the singular car. In A Dictionary of Modern American Usage Garner says “the noun that follows is often plural
<each other’s cars>, but the more logical construction is singular <each other’s car>.”

Did he say “logical”? When it comes to each other and one another, logic is beside the point.