 Marxist theory was a creature of its time, a time when intellectual thought was dealing with social development (or "evolution"), causal necessity, Hegelian philosophy, economically based ideologies and the search for social theories.Marxism is dated by its search for unifying causality, since while the idea of unifying causality was typical of mid 19th century science, it was abandoned in later scientific thought, to be replaced by the idea of invariance, which describes how different phenomena relate to each other, rather than ascribe a single cause for all phenomena.