989: Assimilation of N Aug 24, 2017

The prefix 'un-' that negates certain words like 'unmanageable' or 'unlockable' does not change based on the word to which it affixes. The prefix 'in-' on the other hand appears in all sorts of ways before some sounds, such as 'il-' in 'illegal' or 'im-' in 'impossible' when it is used to negate the meanings thereof. In fact, this also happens when the prefix is used to indicate 'in' or 'into', as this phenomenon is due to phonology. As it happens, when written, it will almost always appear as 'il-' before the letter L, 'im-' before a B, M, or P, and as 'ir-' before the letter R, as in 'irrespecitve'. Indeed, the sound changes in speech too of course, but not only does this occur when 'in-' appears as a prefix, but also when it is used as its own word. It is much less work for the /n/ sound to be produced like a /m/ before certain aforementioned sounds like /p/, and because /m/ and /n/ don't sound especially different, particularly when there is context, everyone will understand. For example, the sound /n/ in 'in' will assimilate to an /m/ in "I spoke French in Paris" as it precedes a /p/, but will not in "I spoke French in France" in ordinary speech. Certainly, though, it is possible to pronounce the word with an /n/ if you are thinking about it.
See yesterday's post for more on this here.