'Never have I seen' is called 'inversion after negative adverbials' When we want to put more emphasis on the negative aspect/ or uniqueness of a situation we can put the adverb at the start of the sentence but then we have to 'invert' the subject and the auxiliary (like in questions) 'I had never seen so many people in a room.' (normal sentence structure) 'Never had I seen so many people in a room.' (inverted sentence structure) When the sentence is in the present or past simple we use the auxiliaries do/does and did. 'Rarely does Bob speak to himself.' http://practiseenglish.blogspot.com/2009/04/grammar-issues-inversion.html http://www.michellehenry.fr/inversion.htm We can also add emphasis to positive sentences in the present and past simple by using the auxiliaries do/does and did . 'I do love him!' 'I did finish my home work!'

Whats the problem? what are you trying to write?

It's just a fancy way of saying stuff: Never/Rarely/Too often... ...have I done that. ...do I do that. ...would I do that. It adds a bit of drama to the never/rarely/too often. You won't need any more information. The rules are clear to see.

This structure is used occasionally, but its not very common in comparison to the normal structure. "Never have I seen" is literally the same exact thing as "I have never seen", and so on. The structure that you're asking about sounds somewhat older. But like I said, it means the same exact thing, and you will not hear it nearly as much as just "I have never seen...", "I rarely find...", etc. Hope this helps a bit :)