Inversion has to be used:

1. After negative adverbials:

a. when the adverbial occurs at the beginning of a clause

Nowhere can I find her.

b. time expressions: never, rarely, seldom used with present perfect or past perfect, or with modal verbs such as can and could, e.g.

Never have I seen such a beautiful house.

Seldom can I remember her name.

c. time expressions: hardly/barely/ scarcely (ledwie, zaledwie, prawie nie), no sooner....than... (zaledwie cos się stało, wydarzyło się coś innego)) used with past perfect, e.g.

No sooner had he put down the receiver than the telephone rang again.

d. after "only" combined with other time expressions (usually with past simple); only if, only when, only then, only later; e. g.:

Only when she is really desperate does she ask for help.

!!! IMPORTANT !!!: When only refers to the state of being the only one here no inversion following it (e. g.: Only one student came to the lecture)

e. phrases containing : under no circumstances, on no account, at no time, in no way, on no conditions, not until, not only; (but also) e.g. :

Under no circumstances will Mary leave the house.

On no account am I going to borrow you any money.

f. little (also in negative or restrictive meaning)

Little did I realize what had happened.

2. After so/such

a. used at the beginning of a sentence:

Such a long holiday did he take that he forgot how to do his job.

So well did she sing that she was offered a record deal.

b. used with so much/so great

So much do I owe to you that I'll be grateful to you till the end of my life.

3. Inverted conditional sentences without If-

three types of If- sentence can be inverted without If-. This makes the sentence more formal and makes the event less likely, e.g.

  • First conditional:

If you go out, leave the key under the mat.

Should you go out, leave the key under the mat.

  • Second conditional:

If I were you, I would apologize.

Were I you, I would apologize.

  • Third conditional:

If he had been invited, he would have come.

Had he been invited, he would have come.

4. After so, neither and nor used in echoing statements, agreeing or disagreeing, e.g.:

Tom: I love pizza!

Mary: So do I. (=I also like pizza.)

Tom: I can't swim

Mary: Neither/nor can I. (I also can't swim)

5. After adverbs of place, e.g. :

Here is your pen!

There goes the rain!