How many negation prefixes are there in English? I knew about ab- an- il- im- in- ir- un-, but ig- is new to me. How many have I missed? And is a- always a variant of an-?
il- im- in- ir- and ig- are almost certainly variants on the same prefix. I think the base is in-, and it varies depending on the root that follows. The 'g' in ig- doesn't strike me as a natural phonological change, so it might be a hang-over from an older language, like the silent 'k' in 'know'.
Ah, my guess is right. See allomorphy in English (pretty far down on the page, under "Allomorphy"), the etymology of ignoble, and a definition of allomorph.
