Frequency: The word is one of the 700 most common words in English.
1.
You use either in front of the first of two or more alternatives, when you are stating the only possibilities or choices that there are. The other alternatives are introduced by 'or'.
Sightseeing is best done either by tour bus or by bicycles...
The former President was demanding that he should be either put on trial or set free...
Either she goes or I go.
CONJ
2.
You use either in a negative statement in front of the first of two alternatives to indicate that the negative statement refers to both the alternatives.
There had been no indication of either breathlessness or any loss of mental faculties right until his death.
CONJ
3.
You can use either to refer to one of two things, people, or situations, when you want to say that they are both possible and it does not matter which one is chosen or considered.
There were glasses of champagne and cigars, but not many of either were consumed...
PRON
•
Either is also a quantifier.
Do either of you smoke or drink heavily?
QUANT: QUANT of def-pl-n
•
Either is also a determiner.
I don't particularly agree with either group.
DET: DET sing-n
4.
You use either in a negative statement to refer to each of two things, people, or situations to indicate that the negative statement includes both of them.
She warned me that I'd never marry or have children.-'I don't want either.'
PRON: with brd-neg
•
Either is also a quantifier.
There are no simple answers to either of those questions.
QUANT
•
Either is also a determiner.
He sometimes couldn't remember either man's name.
DET
5.
You use either by itself in negative statements to indicate that there is a similarity or connection with a person or thing that you have just mentioned.
He did not even say anything to her, and she did not speak to him either...
ADV: ADV after v, with brd-neg
6.
When one negative statement follows another, you can use either at the end of the second one to indicate that you are adding an extra piece of information, and to emphasize that both are equally important.
Don't agree, but don't argue either...
ADV: ADV after v
7.
You can use either to introduce a noun that refers to each of two things when you are talking about both of them.
The basketball nets hung down from the ceiling at either end of the gymnasium...
DET: DET sing-n