Learn English – “Everyone put on his coats” or “everyone put on their coats”

As the other answers might suggest, we could start by considering four alternatives here, to identify two problems of agreement:

1. Everyone put on his coat.
2. Everyone put on his coats.
3. Everyone put on their coat.
4. Everyone put on their coats.

I agree with Jay in ruling out forms 2 and 3, which distract us with the question of whether each person had one coat (as I assume you meant), or whether the people have several coats each (form 2) or share one coat (form 3), considerations that seem silly.

So we are down to choosing between forms 1 and 4.

Many native speakers would certainly say form 4 in ordinary speech. They seem to think of "everyone" as meaning "they all," and proceed as if they had actually said that instead: they all put on their coats.

To me, that seems wrong. Everyone means "each person," and is singular, allowing only form 1. But there are some sticky points about choice 1.

First, I guess, form 1 sounds stilted. But secondly, there might be contexts in which the listener cannot be trusted to follow you in treating "everyone" as singular. For example, consider this story:

John invited his co-workers to meet him after work. At the end of the day everyone went back to his house.

That story seems to dare the reader to guess whether each person went to his own house, or whether all people met at John's house.

So for those people who are conscious of the problem, perhaps the best solution would be to think about each use of such a construction. Treat "everyone" as singular, but if this results in confusing prose, in which the reader cannot tell whom you refer to, rewrite using legitimately plural words instead:

John invited his co-workers to meet him after work. At the end of the day...

a) they all went back to his house; or

b) each person went to his own house.