According to Marx, the social contradiction which can
only be resolved by revolution is that between the
forces of production and the relations of production.
The most common Marxist interpretation of this
assertion is that forces of production means capital
(sometimes our latter‑day Marxists implicitly
limit this to technology, so that the "full
development of the forces of production" is
interpreted solely as the presence of advanced, highly
productive machinery) while relations of production
means the system of production, appropriation, and
exchange.
In reality, Marx meant something quite different.
Forces of production includes both capital and labor,
while relations of production includes capitalists and
workers. Thus the proletariat is an essential of both
sides of the antagonism—on one side as the creator of
use value, on the other as wage laborer. The
contradiction is therefore internal and essential to
the working class itself, and cannot be resolved
externally."