Finally, dialectical materialism is opposed to existentialism and to its essential indeterminism, because, in fact, our mental life is perpetually conditioned by the situations in which it is engaged, be they in accord with its own propensities or contrary to them. But relationships between the organism and the environment are further enriched by the fact that the environment itself is not constant. A change in the environment may result in either the extinction or the transformation of the organisms existing within it. Thus, it becomes the role of different environments, according to their differences, to evoke or bring to the fore different capacities, already potentially present, in a species or in individuals. In the history of mankind, therefore, a succession of different civilisations has given rise to diverse forms of activity.
Historical materialism extends and crowns dialectical materialism.
In transforming the conditions of his life, man transforms himself. In human activity speech has served as the instrument of a transformation that has brought speech by degrees from purely muscular activity to theoretical activity, entailing a reorganisation of cerebral operations. This does not mean, however, that the second activity has replaced the first. Through language, the conceptual sphere has acquired an organisation and structure based on stable, coherent, and logical systems. Our impressions and actions for the most part terminate in, or proceed from, this sphere.