This one could be interpreted a number of ways, and most of the
interpretations could be answered with a book. I'm going to take
a shot at it anyway. In Marxism, the bourgeoisie is the class
that owns the means of production. This can be direct ownership
of, say, a factory or train; or it can be a nice stock
portfolio. The key point is that you are deriving most of your
income, not from your own labour, but from charging others for
the use of your property. The proletariat is the class of people
who earn their money by working. 'Middle class', on the other
hand, could be taken to refer to white collar workers - people
who do mental as opposed to physical (blue collar) work. There
is a parallel with the bourgeoisie, which I don't think Marx
foresaw (I'm not all that familiar with his work though) - white
collar work tends to require a certain amount of education,
which can be viewed as a one time investment which the 'worker'
then uses to generate income for the rest of his life. I think
those are reasonable d