Does blacklist block entire phrases or word sets?Or it only blocks single words?

I wanna know whether WordPress comment blacklist can block word sets or phrases (for example: “son of a”) or it blocks only single words within a set (for example, if “son of a” is on my list, all comments containing “son”, “of” or “a” are blocked).

I’m having the problem of the system throwing into spam folder too many false positives – legitimate comments incorrectly treated as spam. And I don’t know whether it’s really Akismet’s fault of because of a limitation on WordPress blacklist.