Yes, they are mutually exclusive. There are two different meanings of "middle class" being used in this kind of discussion: 1. The class of people who live of

Yes, they are mutually exclusive. There are two different meanings of "middle class" being used in this kind of discussion: 1. The class of people who live of their work but owns their own means of production (e.g. independent professionals like dentists, lawyers, or independent tradesmen like plumbers, electricians). This definition sits in the middle between the working class (who has to work for an employer) and the ruling class (who employs others to work for them). 2. The class of people with the middle earnings, regardless of how they earn their money. This definition sits in the middle between the poor and the rich. So, if you are comparing middle class and working class you are clearly using meaning #1, in which case they are mutually exclusive by definition. To be clear, not everyone who works is working class, the working class is just those who have to sell their labor to a middleman because they don't own the means to work directly to a customer.