Inversion refers to an irregular verb placement form:

Use of Question Form In this case, the question form (auxiliary + subject + main verb) takes the place of the standard positive sentence structure: Examples :I not only enjoy classical music, but I also have a season ticket to the symphony.Not only do I enjoy classical music, but I also have a season ticket to the symphony.

Negative Adverbials Time expressions: never, rarely, seldom

I have never been more insulted!Never have I been more insulted!

He has seldom seen anything stranger.Seldom has he seen anything stranger.

Time expressions: hardly, barely, no sooner, or scarcely

As soon as he had finished dinner, she walked in the door.No sooner had he finished dinner, than she walked in the door.

After 'Only‘: Expressions such as 'only after', 'only when', 'only then', etc.

I only understood the problem then.

Only then did I understand the problem.

The teacher only makes a comment after understanding the situation.

Only after understanding the situation does the teacher make a comment.

After 'Little' 'Little' is used in a negative sense.

He understood the situation very little.

Little did he understand the situation.

I have read little concerning nanotechnology.

Little have I read concerning nanotechnology.

Inverted Conditional Forms Sometimes conditional forms are inverted as a means of sounding more formal. In this case, the conditional 'if' is dropped and the inverted forms take the place of the 'if clause'. If he had understood the problem, he wouldn’t have committed those mistakes.Had he understood the problem, he wouldn't have committed those mistakes.

If he should decide to come, please telephone.Should he decide to come, please telephone.