depends on the condition.
The intention of most snow pants is to be worn over the normal pants.
But I have been known to not include the normal pants due to the cotten factor in the normal pants thatI had on hand at the time.
I'm kinda like him. Usually if it's cold enough for snow pants I've got some long johns or running tights underneath. But I really never wear them other than skiing, when it's just those 2 layers. If I was camping, it'd probably be over whatever pants I wore to get to the base camp, when I'd don the snow pants.