Learn English – the opposite of “Coexist”

antonymssingle-word-requests

Is there a good phrase or word that means the opposite of "coexist"?

The phrase I am using it in is similar to "these two ideas need not (be) __."

Best Answer

Mutually exclusive

Two things that can't happen at the same time.

http://en.wikipedia.org/wiki/Mutually_exclusive_events