An ELT Glossary : Subject Verb Inversion

There are two types of subject-verb inversion in English :

a) Inversion of subject and main verb

Round the corner came a large procession.
Here's John now.
Down fell the rain!

This type of inversion only happens under certain conditions :

a) The verb is an intransitive verb of position (be, lie, stand,sit etc) or of movement (come, go, fall, rise etc).

b) The verb phrase consists of one word only (ie Down fell the rain but not *Down is falling the rain.)

c) The topic of the phrase is an adverbial of place or movement (In the examples : Round the corner, Here, Down)

d) The subject is not a personal pronoun (ie Here's John now but Here he is now, not *Here is he now.)

b) Inversion of subject and operator

This happens in a number of constructions in English :

a)  In question formation : 
Are you listening? / What did you say?

b) In exclamations : 
Wow, was he angry! / Am I hungry! / Did he look silly!

c) After negative or "limiting" adverbials : 
Under no circumstances should you tell David. / Only afterwards did they fully understand what had happened. / Little did he expect to see Jean there. /Hardly had I started talking when he interrupted me.

d) When so/neither are used as substitute forms with the meaning of addition :
A : Jane lives in Eltham. B : Really? So does Malcolm. /  A : I haven't seen him for three days B : No, neither have I

e) As an alternative form to the "if" clause in some so-called "conditional" structures :
Had you told me, I wouldn't have gone / Should he arrive, call me. / Were he to agree, there'd be no problem