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.

Advances in science help to delegitimize the rule of kings and the power of the Church.

There is no greater stupidity than for people...to marry and so surrender themselves to the small miseries of domestic and private life.

All social life is essentially practical. All mysterious which lead theory to mysticism find their rational solution in human practice and in the comprehension of the practice.

Religion is the opium of the masses.

Parliamentary cretinism: that peculiar malady which since 1848 has raged all over the Continent, which holds those infected by it fast in an imaginary world and robs them of all sense, all memory, all understanding of the rude external world.

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.