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)

As for slavery, there is no need for me to speak of its bad aspects. The only thing requiring explanation is the good side of slavery. I do not mean indirect slavery, the slavery of proletariat; I mean direct slavery, the slavery of the Blacks in Surinam, in Brazil, in the southern regions of North America. Direct slavery is as much the pivot upon which our present-day industrialism turns as are machinery, credit, etc. … Slavery is therefore an economic category of paramount importance.

Beauty is the main positive form of the aesthetic assimilation of reality, in which aesthetic ideal finds it direct expression.

Religious distress is at the same time the expression of the real distress and also the protest against real distress. Religion is the sigh of the oppressed creature, the heart of a heartless world, just as it is the spirit of the spiritless condition. It is the opium of the people.

Darwin has interested us in the history of nature's technology.

Hazrat Mahal, Begum of Oudh, during the national liberation uprising of 1857-59 in India headed the rebels.

The imaginary flowers of religion adorn man's chains. Man must throw off the flowers, and also the chains.