In Harry Potter III, my attention was caught by the following construction:

Hermione and Ron were looking daggers at each other, and when they got into class, they seated themselves either side of Harry;

Why the preposition "on", or maybe another one, was not put before "either side"?

At first, I was thinking that the answer may be connected with the transitivity of the verb "seat", which was used here instead of the intransitive "sit" / "sit down". But then I searched for another examples in HP. That's what I have found:

He and Hermione sat down on either side of Ron
They went to sit down either side of her.
the Bulgarian Beaters <..> had landed either side of Mostafa
<..> and settled themselves in chairs on either side of him.

I see virtually no difference between "on either side" and "either side". Am I right? Can I use them interchangeably in speech and writing?

  • 2
    The mean the same thing in the U.K. In the U.S., we usually say on either side. Commented Jan 19, 2019 at 20:18
  • See Google Ngrams for evidence. Commented Jan 19, 2019 at 20:19
  • Peter Shor, thank you. The link to Google Ngrams is very helpful. I wiil be aware of this tool from now on.
    – user74785
    Commented Jan 19, 2019 at 23:59

1 Answer 1


From an American English perspective, this is one of those constructions where "on either side" and "either side" mean the same thing, but there are differences. In a more archaic or extremely formal tone, one might drop the preposition here (or maybe emulating a more UK style). Spoken, this omission in the phrase would go unnoticed, although generally it's more correct to use the preposition "on". In any type of writing, one can never go wrong by using "on".

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