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Metaphysicians hold that all the different kinds of things in the universe and all their characteristics have been the same ever since they first came into being. All subsequent changes have simply been increases or decreases in quantity. They contend that a thing can only keep on repeating itself as the same kind of thing and cannot change into anything different. In their opinion, capitalist exploitation, capitalist competition, the individualist ideology of capitalist society, and so on, can all be found in ancient slave society, or even in primitive society, and will exist for ever unchanged. They ascribe the causes of social development to factors external to society, such as geography and climate. They search in an over-simplified way outside a thing for the causes of its development, and they deny the theory of materialist dialectics which holds that development arises from the contradictions inside a thing. Consequently they can explain neither the qualitative diversity of things, nor the phenomenon of one quality changing into another. In Europe, this mode of thinking existed as mechanical materialism in the 17th and 18th centuries and as vulgar evolutionism at the end of the 19th and the beginning of the 20th centuries. In China, there was the metaphysical thinking exemplified in the saying "Heaven changeth not, likewise the Tao changeth not", [4] and it was supported by the decadent feudal ruling classes for a long time. Mechanical materialism and vulgar evolutionism, which were imported from Europe in the last hundred years, are supported by the bourgeoisie.
As opposed to the metaphysical world outlook, the world outlook of materialist dialectics holds that in order to understand the development of a thing we should study it internally and in its relations with other things; in other words, the development of things should be seen as their internal and necessary self-movement, while each thing in its movement is interrelated with and interacts on the things around it. The fundamental cause of the development of a thing is not external but internal; it lies in the contradictoriness within the thing. There is internal contradiction in every single thing, hence its motion and development. Contradictoriness within a thing is the fundamental cause of its development, while its interrelations and interactions with other things are secondary causes. Thus materialist dialectics effectively combats the theory of external causes, or of an external motive force, advanced by metaphysical mechanical materialism and vulgar evolutionism. It is evident that purely external causes can only give rise to mechanical motion, that is, to changes in scale or quantity, but cannot explain why things differ qualitatively in thousands of ways and why one thing changes into another. As a matter of fact, even mechanical motion under external force occurs through the internal contradictoriness of things. Simple growth in plants and animals, their quantitative development, is likewise chiefly the result of their internal contradictions. Similarly, social development is due chiefly not to external but to internal causes.
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