During four decades Frederick Engels worked closely with Karl Marx in organizing the communist movement and developing communist theory. They created a kind of division of labor in their writing. Engels wrote about military matters and natural science, Marx wrote on economics, and they both wrote about politics and history.
Engels also worked on popularizing and defending dialectics. In private, Engels was quite critical of Marx's sometimes very difficult presentation of dialectical ideas in Capital. He wrote that a reader who hasn't been to college "will certainly not be pleased to torture himself" in order to understand what Marx wrote there about the contradiction between the use of a commodity and what it costs.
Engels wrote several articles and books that tried to make dialectics clearer, and he also made genuine contributions to the theory of dialectics. We will discuss some of his main ideas in this column and the next.

Dialectical Versus Metaphysical Thinking
Engels used the term "metaphysical" to describe anti-dialectical thinking. This is not the only way to use that term in communist philosophy. Metaphysics can also describe questions about the basic make up of the universe, so that idealism and materialism are fundamentally opposed views in metaphysics. As Engels used the term, however, metaphysics means a kind of rigid thinking that denies the interconnection of opposites. Opposites like the working class and the capitalist class don't have a strict dividing line. Some people, like movie stars or elite professional athletes, don't fit neatly in either category. Some workers go into business and some capitalists go bankrupt and have to get a job.
Engels said that this is typical of opposites, that they don't have rigid divisions but each side crosses any dividing line and penetrates into the other and the relationships of the two sides change over time. This kind of relationship is called "interpenetration" of opposites. Denying interpenetration is "metaphysical thinking," which tries to impose arbitrary categories on reality.
Engels said that "nature is the proof of dialectics" and gave many examples from natural science of metaphysical versus dialectical thinking. Darwin's theory of evolution, for example, overthrew the metaphysical idea of a species as an unchanging category that is sharply divided from every other species. Scientists have been able to discover many intermediate cases between classes of animals, like those between giant dinosaurs and birds.
Engels also saw Darwin's theory as an example of the relationship between the philosophical concepts of chance and necessity. He pointed out that the necessary process of natural selection depends on mutations, which are chance variations in an organism's genes. So in evolution, chance and necessity are opposites that "interpenetrate" and depend on each other.

Contradiction and Interpenetration of Opposites
The fact that conflicts and contradictions cause change, which is the heart of dialectics, is closely connected with the interpenetration of opposites. Engels rejected the idea that a dialectical contradiction can simply be defined as a pair of forces pushing or pulling in opposite directions, like a game of "tug of war." This definition is wrong because it leaves out the connection between contradictory sides, where each side partly determines what the other side is. For example, imperialist powers planning for war have to match the weapons systems of their opponents. Some members of the working class take on characteristics of the capitalist class, like selfishness, greed, and racism.
Engels considered the interpenetration of opposites to be a law of dialectics. In the next column we will see what he meant by calling this a law and discuss two more of Engels' laws.

Clarification of the last column:
In our last issue we reviewed some of Marx's ideas about how real contradictions develop, that is, head toward resolution. Development typically involves a contradiction's becoming more clearly defined and more obvious. It also involves a more intense struggle between the two sides of the contradiction and changes in the motion that the contradiction causes.
The column described development as becoming sharper, more clearly defined and more obvious, rather than making it clear that it is the contradiction that becomes sharper, more obvious, etc. during its development.