I'm no expert - I haven't read Hegel's Logic, nor, except for bits, even Engels' Anti-Duhring. I am not qualified to write a history of ideas - what did Marx himself really think? - nor do I find that question very interesting. But I do think I have read and heard enough arguments on the topic to begin to judge their substance.
John Rees* gives the following definition of the "essentials" of the dialectic:
- The world is a constant process of change;
- The world is a totality; and
- This totality is internally contradictory.
Per Rees, the triadic "thesis"/"antithesis"/"synthesis" pattern which is commonly associated with the dialectic, where the contradictory existence or validity of thesis and antithesis results in a new state or idea, the synthesis, which subsumes and transforms both, is then simply one form taken by such dynamic, contradictory totalities. The phrase "unity of opposites", also associated with dialectics and sometimes called a "law", describes the relationship between thesis and antithesis in this kind of triad. The "negation of the negation", another "law", is a yet more specific version of the triad, in which the thesis comes first, then is apparently defeated or subordinated by the antithesis, which finally is defeated or subordinated by a new synthesis that contains elements of the original thesis. The last common "law", the "transformation of quantity into quality", is, on the other hand, a characteristic of how dialectical transformations more broadly take place: a contradictory set of forces will push a system in one direction without fundamentally changing its character for some time, but eventually the changes will add up to a new and fundamentally different configuration.
Some more-concrete examples of dialectically contradictory totalities, in Marxist theory: The interdependent relationship between the economic "base" of society and the political and cultural "superstructure". The class struggle between bourgeoisie and proletariat under capitalism and the possibility of socialism as its result. The relationship between productive forces and the mode of production, where capitalism at first advances production and then begins to weight it down through crises. The role of a revolutionary party as both an element of working class consciousness and an actor upon it.
According to a dialectical interpretation, each of these systems is a totality in that its parts are inseparable from one other and can have no independent existence, but are rather aspects or "moments" of one coherent whole, abstracted and treated as separate only in thought, as a means of systemic analysis. (There can be no base without a superstructure, no party without a class.) Each system is contradictory, either containing some kind of struggle, or described by multiple propositions which are somehow opposite but are simultaneously true. (The bourgeoisie and proletariat are at war, the party both acts and is acted upon by the class.) Finally, the contradictions are what propel the system forward - if not for the contradictions, the system would be static, but they give it the possibility of becoming something new. (Capitalism may become socialism not because someone had an idea which wins out in a side-by-side comparison but because it creates its own gravediggers.)
I do think there is something to these examples - their "dialectical" aspects as just described are real and important. But that leaves many questions unanswered.
The key terms, "totality"/system/process, "contradiction"/opposition, and change/motion/transformation, have not been defined. How broadly does the dialectic apply - to nature, to society, or merely to elements of capitalism? Are its laws akin to those of logic and math, to those of physics, or to the more-or-less approximate generalizations of, say, biology - or are they simply rules-of-thumb, useful pointers? Is the dialectic a set of connected theses, propositions about the world as a whole, or is it a structure which things may take, which implies certain properties, or is it a grab-bag of fundamentally unrelated adjectives which sometimes apply together but only coincidentally?
I want to try to answer these questions, at least to my own satisfaction, in following posts.
* The Algebra of Revolution, p. 114. This is an interesting and useful survey of Marxist thinking about dialectics despite Rees' tendency to elide hard questions.