Philosophy stands in the same relation to the study of the actual world as masturbation to sexual love.

Greek philosophy seems to have met with something with which a good tragedy is not supposed to meet, namely, a dull ending.

A nation that enslaves another forges its own chains.

In the bureaucracy, the identity of state interest and particular private aim is established in such a way that the state interest becomes a particular private aim over against other private aims.

The alienation of man thus appeared as the fundamental evil of capitalist society.

Labor, being itself a commodity, is measured as such by the labor time needed to produce the labor-commodity. And what is needed to produce this labor-commodity? Just enough labor time to produce the objects indispensable to the constant maintenance of labor, that is, to keep the worker alive and in a condition to propagate his race. The natural price of labor is no other than the wage minimum.

Once the inner connection is grasped, all theoretical belief in the permanent necessity of existing conditions collapses before their collapse in practice -- Letter to Ludwig Kugelmann (July 11, 1868)