How did 'mad' come to be a determiner?

There's a group of words — I think they're called determiners — used to indicate number in some way... like many, few, most, etc. During a linguistics class my professor said this was a closed group of words, and that new ones couldn't really fit in it. Then someone shouted out "There's mad people in here!" and everyone laughed. (Mad meaning many, the usage I'm referring to).

How did mad come to fit in this supposedly closed group? Are there other words that were newly coined to fit there?

Solution 1:

I think it was probably never a determiner but more likely an intensifier. As such, it is a synonym for "insane" as in "That guitar player had insane chops." I hear it most often in terms of having "mad skills" and so forth. In such cases it doesn't mean many, but something more like great or prodigious.

The earliest reference I can think of offhand is from the 2000 film Training Day, in which Denzel Washington tells Ethan Hawke (after Hawke has single-handledly subdued two would-be rapists), "You got mad squabbles, boy." He doesn't mean "many" squabbles, but excellent capabilities in that respect.

If it is ever used to mean a quantity, I think it probably is used as an intensifier and the determiner is left out. Compare it with the Boston area's "wicked" and California's "hella" — they're all used in somewhat the same way.