Mankind always sets itself only such tasks as it can solve; since, looking at the matter more closely, we will always find that the task itself arises only when the material conditions necessary for its solution already exist or are at least in the process of formation.

The only antidote to mental suffering is physical pain.

There is no royal road to science, and only those who do not dread the fatiguing climb of its steep paths have a chance of gaining its luminous summits. (Preface to the French edition).

In place of the old bourgeois society, with its classes and class antagonisms, we shall have an association in which the free development of each is the condition for the free development of all.

Man makes religion, religion does not make man

A heavy or progressive or graduated income tax is necessary for the proper development of Communism.

You will have to go through 15, 20, 50 years of civil wars and national struggles not only to bring about a change in society but also to change yourselves, and prepare yourselves for the exercise of political power.