In Das Kapital, Volume 1 (1867), Karl Marx laid out his critique of political economy. According to Marx, all his predecessors and contemporaries had failed to grasp capitalism for what it truly is: value in motion. Value is created by the exploitation of labourtime - in other words: capitalism presupposes the existence of a capitalist and a labour class. In essence, surplus value (s) is created by variable capital (v) transforming constant capital (c) into new commodities that the capitalist will sell dear on the market.
In Volume 1 of Das Kapital, Marx zoomed in on how surplus value is created in the production process (i.e. on the exploitation of labourers). In Volume 2, Marx was determined to set out how capitalism functions as a system of circulating capital: value creating surplus value, surplus value creating more surplus value, etc. Marx never got to finishing this project (as well as Volume 3), and Friedrich Engels published Volume 2 out Marx' manuscripts, adding and deleting material here and there. The result is a very incoherent, unfinished and incomplete work.
But Das Kapital Volume 2 (1885) is not only incomplete, it is also very abstract. This has nothing to do with the state of Volume 2 when Marx passed away; it has everything to do with Marx' approach to present the material. In essence: Marx uses the method of critical analysis to study capitalism and discover the natural laws determining this economic system. He does this out of necessity, since he wants to offer a scientific analysis of capitalism. The scientist wants to do controlled experiments - i.e. singling out one variable for variation, while holding all other variables constant. This is, of course, impossible to achieve in economics. (This, by the way, is a problem that still pesters modern day economics - some critics use this problem to argue that economics isn't even a science.)
Anyway, Marx studies capitalism on a very abstract, general level. He then zooms in on particular phenomena, and assumes all other interrelated phenomena are given. So when he presents his results, one has always to add this caveat to his conclusions. By following this method, he discovers interesting lawlike tendencies in the capitalist system and interesting questions that were never before raised by scientists. For example, the aim of capital is to reduce the time spent on producing commodities (i.e. the working period) and the time spent on buying and selling commodities (i.e. the circulation period). Why? The faster the process in which a given capital is applied to create surplus value and is again re-invested (i.e. the turnover rate), the more profit the capitalist makes. One can only discover this lawlike tendency in capitalism by zooming in on the cycle of circulation, production and (again) circulation of commodities.
In part 1 of Volume 2, Marx explains the three forms in which capital exists: (1) money capital, (2) production capital and (3) commodity capital. Capital takes on these forms successively in the system of capitalism. The three processes associated with these three forms of capital are circulation (of money), production (of commodities containing surplus value) and circulation (of the produced commodities).
Then, in part 2 of Volume 2, Marx zooms in on how the individual capitalist is affected by the aforementioned forms and processes of capitalism - all the while ignoring technological change, competition, credit, etc. The individual capital consists of the means of production (constant capital), labourtime (cariable capital) and the created value (surplus value). This was already outlined in Volume 1. Now Marx makes a new distinction, between fixed and circulating capital. The interplay and peculiarities of fixed and circulating capital are what truly determines the movement of capital.
Fixed capital transfers its use value, at the hands of the labourer, step by step onto the commodities that are produced. Once the use value of the fixed capital is completely transformed into commodities (i.e. the machine is used up), the capitalist has earned back all his capital spent on this fixed capital. With this capital, the capitalist then buys a new machine. Of course, once one includes continuous technological improvements and inventions (leading to cheaper and more efficient machines) as well as competition by other capitalists, it's easy to see that there's an inherent drive in the capitalist system of production to reduce the turnover rate (i.e. the time in which the capitalist completely earns back his invested money). If you buy a machine for 5000 dollars, which is completely used up in 10 years, you earn back each year 500 dollars of your original investment. I.e. the turnover rate of this machine is 10 years. But once some competitor buys new, cheaper and/or more efficient machinery in the third year, your machine will be worth less on the market, you will not get back the original capital you spend on your machine, so you lose capital. The quicker you wear out your machine, the safer you are, and the more profit you will make. How to achieve this? By instituting 24 hour working days, by making labourers work in shifts, by not stopping machines even for repairs, etc.
Marx uses a major part of part 2 to criticize earlier economists like Adam Smith, David Ricardo and Francois Quesnay. According to Marx, these economists have failed to grasp capitalism for what it truly is: a system of creating surplus value (C = c+v+s). They all focused on the distinction between fixed and circulating capital, failing to see how the distinction between constant (means of production), variable (labour time) and surplus capital (surplus value) is the truly important one to understand capitalism. Surplus (s) gets created out of nothing by making labourers (v) work on the means of production (m). Once you understand this, and understand the difference between the make-up of capital on the one hand and the type of capital (fixed and circulating) on the other hand, you truly grasp capitalism for what it is: exploitation of labour, or even more crudly, the existence of class relations.
The system of individual capital can be described in terms of the time necessary to produce commodities (production time, including the working period) and the time necessary to buy the commodities necessary to produce and the time time necessary to sell your newly produced commodities on the market (both circulation time). Since capital is value in motion, the system of production and circulation has to keep running. And this is where the biggest flaw (in Marx' terms a fatal contradiction) in capitalism lies. We know from experience that it takes time and effort to buy and sell products, that markets fluctuate, that stocks will form, that production will require more time than simply the time to produce a product (e.g. trees have to grow, cattle has to be raised), etc.
This is where the credit system comes in. The individual capitalist will need more money than is simply required for production - he will need money to buy a stock of commodities (in order to keep the production process going), to produce new commodities when the old batch is brought to the market, etc. So banks and speculative investors will loan the capitalist money, or he will put in more of his own money, in order to keep the process of production and circulation going.
But the credit system can only do so much. It can temporarily smoothen things a bit, but it cannot solve the inherent flaws of the system. When stocks start to accumulate on the market, prices will tend to drop, hence surplus value will be destroyed, and since this is someone's capital (the merchant or the capitalist), problems will erupt. Similar problems arise when capitalists start to compete with each other. There are many weak spots in the processes of production and circulation that are dangers to the continuous flow of capital - and these weak spots are the causes of crises. According to Marx, consequently, the capitalist mode of production is inherently instable, stable conditions are only temporary events.
Then, in part 3 of Volume 2, Marx leaves the perspective of the individual capital and he zooms in on the collection of all individual capitals: the social capital. Social capital (just like individual capital) consists of constant, variable and surplus capital. There are two major groups, or departments on the level of society: (1) the production of means of production and (2) the production of the means of consumption. As any labourer, as well as capitalist, has to consume to keep living, consumption becomes a major component of capitalism on the level of social capital. The variable and surplus capital of department 1 is spent on the constant capital of department 2: the commodities of department 1 form the means of production (i.e. constant capital) of department 2.
At the same time, the variable and surplus capital within department 2 are spent on consumption as well (since the labourers and capitalists producing means of consumption have to eat as well), so within department 2 (the production of means of consumption) there's an internal flow of capital as well. All these flows of capital (between department 1 and 2 and within department 2) are mediated by money - this is were the merchant and investor come in. But where does the constant capital (the means of production) in department 1 (the production of the means of production) come from? Well, according to Marx this is partly natural resources and partly the product of its own process (so department 1 produces the means of production for itself as well).
This is all very technical and abstract, but the main point here is that from the perspective of society, the total surplus value is created by setting to work (or exploiting) the total variable capital, the labour force, on the total constant capital, the means of production. Since all people, labourer and capitalist alike, have to eat, live, etc. (i.e. consume), the production of the means of consumption emerges on a societal level. So, the highly general process of capitalist production is divided up into the production of the means of production (department 1) and the production of the means of consumption (department 2). Both departments are related, in that department 1 produces the necessities for department 2 and both departments live of the created use value of department 2 (i.e. everyone consumes).
How does capital accumulate, or expand, on a societal level? Within department 1, production of the means of production, this is simple: the labour forces literally creates surplus value for the capitalist. In other words: the exploitation of the labourer creates 'free' means of production that the capitalist can either sell (to capitalists from department 2) or use himself to expand the scale of his own production.
The humanity of the people making up department 1 forms the basis for the accumulation of capital within department 2. The capitalists and workers that produce means of production have to consume in order to produce. They will spend capital on commodities that are produced by department 2 (the production of the means of consumption). So workers produce capital that is then used as means of production to produce means of consumption; these means of consumption are bought by all people within society. So we here see a nice, neat cyclical process of consumption and production.
One can see how the analysis of the capitalist mode of production (i.e. the circulation of capital through its various stages and forms) on the level of society leads to the same conclusion as Marx already drew in Das Kapital Volume 1, i.e. that the whole system of creating surplus value is based on the existence of an exploitable labour class. Without the existence of this class, society could never produce surplus value in both departments of production. This, by the way, makes it easy to see what one needs to do in order to destroy capitalism: extinguish the class relations. Once the class relations disappear, no more surplus value is being created, and hence the capitalist mode of production breaks down. This is, of course, the message Marx and Engels preach in their Communist Manifesto, this was the aim of their Workers International, and this is what socialists and marxists have tried to put into practice ever since the time of Karl Marx. Uplifting the labour classes means the destruction of capitalism; collective production (i.e. communism) means the destruction of capitalism; forming trade unions and actively working against the fundamentals of capitalist mode of production (e.g. the creation of a reserve army, the suppression of wages, etc.) means the destruction of capitalism.
(For the record: I am not describing my own opinions here, I am just following Marx's argument to its logical conclusion.)
I am glad I re-read Das Kapital Volume 2, since this made me see the ingenuity of Karl Marx' approach to economics. Even though I don't subscribe to his conclusions - I do subscribe to much of his critical analysis of capitalism. Marx exposes the inherent flaws within this economic system - the necessity of continuous circulation of capital and the importance this gives to the (global]) credit system - and the dangerous tendencies of capitalism - the formation of monopolies, the exploitation of man and nature, the elevation of the means (making profits) to a goal in and of itself.
Based on the content of both books, I prefer Volume 2 over Volume 1 - the problem is that Volume 1 is written a much more accessible style and a more livelier and policially inflammatory way. Volume 2, is simply put, a book that doesn't give up its secrets very easily. The question is: does one have the motivation to struggle through this.