Rule: When a negative adverb or adverbial phrase occurs first in a clause, subject and verb are inverted.
Examples of errors:
Inversion of subject and verb means the subject and verb have interrogative word order. As in questions, it is the auxiliary verb, be or have which is inverted, if one of these is present. If not, do is inserted in inverted position (cf. (7), (9)). Subjects include the existential or grammatical subject there (cf. (6)). The adverbs which cause subject-verb inversion in initial position include: never, nowhere, no sooner. not only, neither, nor, no more, no longer, seldom, only, hardly, scarcely , barely, rarely, little, under/in no circumstances, on no account, by no means, in no way, etc. The tone of such inversion is always rather formal, rhetorical or literary, with the non-inverted alternative preferred in ordinary speech and writing, e.g.:
Never have I read a more curious book. (more formal)
I have never read a more curious book. (less formal)
There are a few non-negative adverbs which in initial clause position--again with rhetorical effect (particularly in story-telling)--cause inversion. These include primarily adverbs of movement: in, out, up, down, round, over, back, etc. If the subject is a pronoun, however, there is no inversion. Compare:
At that point, in strode the man of whom we had just been speaking.
Round the corner came two huge German shepherds.
Out you go, you little rascal!
So down to the basement I went.