full statement + linker + shortened statement with auxiliary
I don't like action movies but Andy does.
In the examples above, the auxiliaries are used to make the sentences shorter.
If we didn't use auxiliaries in this way we would have to repeat some words:
I don't like action movies but Andy likes action movies.
I don't like action movies but Andy likes them.
When the first part contains an auxiliary...|
When the first part of the sentence - the part we don't want to repeat - contains an auxiliary, we use that auxiliary in the second part:
Auxiliary verb have
I have never been to Australia but Donna has.Auxiliary verb did
I didn't see the film but the others did.
When the first part does not contain an auxiliary...|
When the first part of the sentence - the part we don't want to repeat - does not contain an auxiliary (e.g. when we use present simple or past simple), we use do / does (present simple) and did (past simple) in the second part:
I like action movies but my brother doesn't.Past simple
I went to the party but Sarah didn't.
When the main verb is be|
When the main verb is be, we can also avoid repetition in this way:
Were you at the meeting yesterday?