We usenot only X but alsoYin formal contexts:
The war causednot onlydestruction and deathbut alsogenerations of hatred between the two communities.
The carnot onlyis economicalbut alsofeels good to drive.
This investigation isnot onlyone that is continuing and worldwidebut alsoone that we expect to continue for quite some time.
We can sometimes leave outalso:
I identified with Denzel Washingtonnot onlyas an actorbutas a person.
To add emphasis, we can usenot onlyat the beginning of a clause. When we do this, we invert the subject and the verb:
Not onlywas it raining all day at the weddingbut alsothe band was late.
Not onlywill they paint the outside of the housebut alsothe inside.
When there is no auxiliary verb or main verbbe, we usedo, does, did:
Not onlydid she forget my birthday,butshealsodidn’t even apologise for forgetting it.
See also:
Inversion