In trying to get a handle on Marx's dialectics, I found the Introduction to the Grundrisse extremely interesting, as I think the logic makes itself more apparent there than elsewhere in our initial readings. In this section, Marx methodically works through the relations between production, distribution, exchange, and consumption, demonstrating how each exists as a moment in a "totality" or in an "organic whole," although production is always the predominant moment. In so doing, Marx also demonstrates how standard cause-and-effect logic is subsumed within dialectics: it has its place but is necessarily limited in its insight.
Marx begins by examining the relation between consumption and production and comes to a threefold concept of the identity between the two. First, production and consumption are related immediately. Every moment of production is a moment of consumption: nothing can be produced without consuming something else at the same time, and nothing is consumed without producing something new. In this sense, production and consumption are two sides of the same moment in the flow of matter from one form to another.
Second, production and consumption are related mediately; they appear as "indispensable to each other" but still "external to each other." In this sense, consumption is a means or condition for production to take place, just as production is a means or condition for consumption. Naturally, without production there can be no consumption: if an object isn't first produced it can't be consumed. However, without consumption production is also impossible, because consumption "creates for the products the subject for whom they are products." A product isn't a product in reality, unless it is really consumed.
Third, and finally, production and consumption are related causatively or creatively. Each moment of production or consumption "creates the other in completing itself, and creates itself as the other." This identity corresponds to traditional logic: production causes consumption and consumption causes production; because of this, Marx acknowledges that this identity is "frequently cited in economics" in the law of supply and demand.
I think that what we see in this threefold identity is Marx's dialectic at work. Just as the first moment in Hegel's dialectic is Being (or, in the "Lordship and Bondsman" chapter, self-consciousness that exists "in itself and for itself,") the first moment in Marx's is the immediate relation between production and consumption-- production is consumption and consumption is production. From this first moment, immediacy comes outside itself and mediates itself through an other: Being is mediated by Notion, one consciousness is mediated by another, and production is mediated by consumption (and consumption by production). Finally, the other is subsumed and the dialectic advances: consumption creates a new moment of production and production creates a new moment of consumption.
Marx is careful to emphasize that production is the real point of departure for this process and therefore holds a sort of predominance over consumption: "The individual produces an object and, by consuming it, returns to himself, but returns as a productive and self-reproducing individual." However, distribution and exchange step in between production and consumption to create further complications and Marx continues to move forward building the network of dialectical relations that holds everything together.
It seems clear to me that the method that Marx demonstrates here is the method of "rising from the abstract to the concrete" that he explains in the section later in the Introduction titled "The Method of Political Economy." Marx starts with the abstract concepts of "production" and "consumption" and works through a dialectical logic to connect them to each other and then later to the concepts of "distribution" and "exchange," slowly making the total process that each of these concepts are a piece of more complete. I would like to better understand this section, however, and the relationship Marx explores between his method and "the process by which the concrete itself comes into being," how his method is related to the real world.