the punchline

[osaraba]

What is curious about ‘em is that contrary to popular belief, the apostrophe does not denote the missing letters “th”. In Middle English ‘em was an alternative form of hem (an old pronoun, not the verb, the clothing term or the throat-clearing interjection), which was later displaced by them. So ‘em does not derive from them; in fact it precedes it.

Preceded by: http://stancarey.wordpress.com/2009/05/19/read-em-and-write-em/