'Either' means one or the other when talking about two items or people. It replaces the noun so you do not repeat it.
Either of the girls can help you.
I don’t like either of the books.
We use 'either' after a negative sentence to add another negative idea. It means 'also not'.
I don’t like coffee either.
She can’t come either.
'Either' can stress that both choices or actions do not happen or succeed. It often appears with negatives.
Neither idea worked, and either was expensive.
He can’t do either task well.
After a negative statement, 'either' means 'also' not. It adds information about something that is also negative.
She doesn’t like apples, and I don’t either.
I can’t swim, and he can’t either.
In logic or math, 'either' means one option or the other, never both. This use is formal and precise.
Either A or B must be true, but not both.
In this problem, either statement can apply, but not both.
In conversation, when someone says they don’t like or can’t do something, 'either' shows that you feel the same way.
I don’t like this song.
I don’t either.
Sometimes 'either' means one or the other separately, but it can imply both options are acceptable together.
Either friend can come with us.
Either day works for the meeting.
