Why use "working class" to mean "blue collar jobs"? Working class is the class of all the people that work for money, and for whom the money earned from said wo

Why use "working class" to mean "blue collar jobs"? Working class is the class of all the people that work for money, and for whom the money earned from said work constitutes all or a large part of their overall wealth. I'm one such person. The vast majority of the people in the US are like that. There are very few people for whom work is optional. All the others are the "working class".