IpseDixit wrote:Can I consistently use 'em in place of them when speaking or is that too informal or denoting low education or something? And are there instances where switching the two of them would be outright ungrammatical?
Assuming you speak reasonably fluidly, I don't know that it would be noticed. Initial /ð/ is often dropped in colloquial speech. Just don't put a glottal stop before it or that will sound odd. And when the pronoun is stressed, dropping the /ð/ would be very jarring.
There's no problem from a grammaticality point of view, but there could be some ambiguity because unstressed 'em and unstressed 'm (for him) can sound very similar, even in dialects (unlike mine) where /i/ and /e/ don't fall together before /m/. Stressed /em/ could be mistaken for "M" or "Em", both of which could be abbreviated forms of personal names ("Em" for "Emily" or "Emma", "M" for any name beginning with "M").