A practical english grammar - Vyssaja skola 1978

Patterns with SO, TOO, NEITHER, EITHER
Sound symbols

If a speaker makes an assertion about one subject and then wants to make the same assertion about a different subject, there are two patterns available in English for doing so, without repeating the predicate in the second sentence. Both patterns use echo verbs.

Неге аге the affirmative patterns.

Henry is a student.

Betty is, too.

So is Betty.

My parents live in California.

Your parents do, too.

So do your parents.

Here are the negative patterns.

Henry didn’t call me yesterday.

Betty didn’t, either.

Neither did Betty.

I haven’t seen your brother.

John hasn’t, either.

Neither has John.

There is no difference in meaning between the two patterns, and most speakers use either one without hesitation. Notice that when too and either are used, the subject and verb are in their usual order; when so and neither are put at the beginning of the sentence, the echo verb precedes the subject.

These patterns can be used only when both assertions are positive or both are negative. If they are not the same, then but must be used.

Henry is a student, but Betty isn’t.

Henry didn’t call me yesterday, but Betty did.