The growing commitment of Jean-Paul Sartre to Marxist political philosophy reaches its maturation in his Critique de la raison dialectique. To many in the non-Communist world, particularly in North America, who have been influenced by his earlier existential philosophy, Sartre's commitment to Marxism seems difficult to explain. Existentialism is a philosophy of individual introspection, whereas Marxism is a philosophy of mass movements. Existentialism denies the reality of absolute values, whereas Marxism postulates the supreme goal of the classless society. Most puzzling of all, the existential philosophy of Sartre himself describes a radical freedom, the negation of all determinism in the lives of human beings; while Marxism is traditionally viewed, both by its proponents and by its critics, as a doctrine of strict determinism.