Hi, We use inversion after negative adverbials to add emphasis, especially in formal or literary styles. Examples of negative adverbials include: never, rarely, hardly, seldom, no sooner, nowhere, and phrases like under no circumstances. For example: • Never have I seen such a beautiful place. • Rarely do we get the chance to meet. • No sooner had he arrived than it started raining. Inversion means the auxiliary verb comes before the subject after these negative expressions.

Howdy Nelly. There are two basic use cases for this. It can have a stylistic function, making the sentence sound a smidge more formal, with perhaps a touch of the poetic. The more common application is to really add emphasis onto the adverb. For example: Non inverted: I have rarely seen such a lousy movie. (Pretty neutral) Inverted: Rarely have I seen such a lousy movie. (Semantically identical, but here you are really drawing attention to the rarity of the event. The movie was not just bad, it was criminally bad.)