Materialist dialectics, a philosophical method for investigating nature and society, holds practical activity to be the basis of our relations with the world and therefore of cognition. Praxis is thus a criterion of knowledge. Only when practical activity confirms the coincidence of ideas and hypotheses with reality can it be said that they are true. Since practical activity is relative to the level of technological development, truth can never be that absolute ardently sought and equally trembled before by the idealists, rather, it is a deepening relative in relation to an absolute which can only ever be theoretical. Lenin wrote:
’From living perception to abstract thought, and from this to practice, such is the dialectical path of the cognition of truth, of the cognition of objective reality. Kant disparages knowledge in order to make way for faith: Hegel exalts knowledge, asserting that knowledge is knowledge of God. The materialist exalts the knowledge of matter, of nature’, V.I.Lenin, Collected Works, Vol., 38 (Philosophical Notebooks), Progress Publishers, Moscow, 1976, 171.
There is nothing in the world but matter in motion, and matter in motion cannot move otherwise than in space and time. Human conceptions of space and time are relative, but these relative conceptions go to compound absolute truth. These relative conceptions, in their development, move towards absolute truth and approach nearer and nearer to it. The mutability of human conceptions of space and time no more refutes the objective reality of space and time than the mutability of scientific knowledge of the structure and forms of matter in motion refutes the objective reality of the external world.
V.I.Lenin, Materialism and Empirio-criticism: Critical Comments on a Reactionary Philosophy, Progress Publishers, Moscow, 1975, 158
Earth at Equinox, September 2013, from the Russian meteorological satellite Electro-L
But dialectical materialism insists on the approximate, relative character of every scientific theory of the structure of matter and its properties; it insists on the absence of absolute boundaries in nature, on the transformation of moving matter from one state into another, that from our point of view is apparently irreconcilable with it, and so forth. However bizarre from the standpoint of “common sense” the transformation of imponderable ether into ponderable matter and vice versa may appear, however “strange” may seem the absence of any other kind of mass in the electron save electromagnetic mass, however extraordinary may be the fact that the mechanical laws of motion are confined only to a single sphere of natural phenomena and are subordinated to the more profound laws of electromagnetic phenomena, and so forth – all this is but another corroboration of dialectical materialism. It is mainly because the physicists did not know dialectics that the new physics strayed into idealism. They combated metaphysical (in Engels’ and not the positivist, i.e., Humean, sense of the word) materialism and its one-sided “mechanism”, and in so doing threw out the baby with the bath-water. Denying the immutability of the elements and of the properties of matter known hitherto, they ended by denying matter, i.e., the objective reality of the physical world. Denying the absolute character of some of the most important and basic laws, they ended by denying all objective law in nature and by declaring that a law of nature is a mere convention, “a limitation of expectation”, “a logical necessity”, and so forth. Insisting on the approximate and relative character of our knowledge, they ended by denying the object independent of the mind, reflected approximately-correctly and relatively-truthfully by the mind. And so on, and so forth, without end.
V.I.Lenin, Materialism and Empirio-criticism: Critical Comments on a Reactionary Philosophy, Progress Publishers, Moscow, 1975, 242-243