Marx's dialectics according to David Harvey:
'One of the most important things to glean from a careful study of Volume I is how Marx's method works. I personally think this is just as important as the propositions he derives about how capitalism works, because once you have learned the method and become both practiced in its execution and confident in its power, then you can use it to understand almost anything. This method derives, of course, from dialectics, which is, as he points out in the preface already cited, a method of inquiry "that had not previously been applied to economic subjects" (104). He further discusses this dialectical method in the postface to the second edition. While his ideas derive from Hegel, Marx's "dialectical method is, in its foundations, not only different from the Hegelian, but exactly opposite to it" (102). Hence derives the notorious claim that Marx inverted Hegel's dialectics and stood it right side up, on its feet.' (Harvey 2010: 11)
In what immediately follows the above, Harvey makes it clear that Marx's dialectics is to understand "processes of motion, change and transformation."
'There are ways in which, we'll find, this is not exactly true. Marx revolutionalized the dialectical method; he didn't simply invert it. "I criticized the mystificatory side of the Hegelian dialectic nearly thirty years ago," he says, referring to his critique of Hegel's Philosophy of Right. Plainly, that critique was a foundational moment in which Marx redefined his relationship to the Hegelian dialectic. He objects to the way in which the mystified form of the dialectic as purveyed by Hegel became the fashion in Germany in the 1830s and 1840s, and he set out to reform it so that it could take account of "every historically developed form as being in a fluid state, in motion." Marx had, therefore, to reconfigure dialectics s that it could grasp the "transient aspect" of a society as well. Dialectics has to, in short, be able to understand and represent processes of motion, change and transformation. Such a dialectical method "does not let itself be impressed by anything, being in its very essence critical and revolutionary" (102-3), precisely because it goes to the heart of what social transformations, both actual and potential, are about.' (Harvey 2010: 11)
Harvey goes on to explain how Marx's dialectics is different from Hegel's and the version of Marx we tend to believe in.
'What Marx is talking about here is his intention to reinvent the dialectical method to take account of the unfolding and dynamic relations between elements within a capitalist system. He intends to do so in such a way as to capture fluidity and motion because he is, as we will see, incredibly impressed with the mutability and dynamics of capitalism. This goes against the reputation that invariably precedes Marx, depicting him as some sort of fixed and immovable structuralist thinker. Capital, however, reveals a Marx who is always talking about movement and the motion - the processes - of, for example, the circulation of capital. So reading Marx on his own terms requires that you grapple with what it is he means by "dialectics." '(Harvey 2010: 11-12)
One example how Marx's dialectics works is seen when he explains the dual aspect of value of the commodity: use-value and exchange value.
'Let us reflect a moment on the structure of this argument. We begin with the singular concept of the commodity and establish its dual character: it has a use-value and an exchange-value. Exchange-values are a representation of something. What is it a representation of? A representation of value, says Marx. And value is socially necessary labor-time. But value doesn't mean anything unless it connects back to use-value. Use-value is socially necessary to value.'
(Harvey 2010: 22)
The dialectics is not about causality, at least uni-directional causality. It is about codependent relations that requires its constituents at the same time.
'How has Marx's dialectical method been working here? Would you say that exchange value, or use-value cause ...? This analysis is not causal. It is about relations, dialectical relations. Can you talk about value without talking about use-value? No. In other words, you can't talk about any of these concepts without taking about the others. The concepts are codependent on one another, relations within a totality of some sort.' (Harvey 2010: 33)