The two essays Wage-Labour and Capital and Value, Price and Profit are succinct summations of Marx's economic observations that of course go nowhere near the depth and examination of the 900 pages of Capital. Nonetheless, read correctly, they provide one with a fair view of just how the exploitation of workers and the production of commodities take place under capitalism.
Marx was writing the first pamphlet in the period directly following the defeat of the 1948 revolutions that rocked Europe. He and many other revolutionaries concluded that these revolutions didn't disprove but affirmed the central historical role of the proletariat as the universal and revolutionary class. Ergo, the need to understand the terms of the proletariat's exploitation was much greater. This is a succinct and schematic pamphlet, easily divided up into short chapters.
What Are Wages? On the surface, it seems that workers receive wages in exchange for their labor. However, Marx asserts that this is an illusion, and that workers are actually selling their labor-power. What is the difference? The labor is, well, the actual labor performed. If a worker were to be fairly compensated for his labor then s/he would be paid the actual value of that labor (whatever added value the labor creates for the commodity), but we shouldn't get ahead of ourselves. The distinction is that labor-power is a commodity for all intents and purposes like any other. The labor power is used up during the time frame stipulated (weekly wages for one week of labor power).
Whatever wages are paid to the worker are, of course, in the form of money, an expression of how many other commodities might be bought with said money. They are also not taken out of the profits made from the commodities s/he made. Marx states that if a bolt of cloth woven by weaver is sold by the owner of the textile mill for twenty shillings, the weaver isn't then given the twenty shillings. The weaver has already been paid because his/her labor-power has been bought, much how the loom and the yarn were bought: as commodities.
Wages then aren't a share of profits but are that specific part of what a capitalist spends on already existing commodities in order to make a finished product. The only distinction is the commodity that it is spent on: labor-power. Consequently, this labor has no importance to the worker past the wages is earns for him or her. How much a capitalist pays for wages is determined by the price of labor as a commodity on the market.
By what is the price of a commodity determined? Supply and demand certainly exists, though with differences from how capitalism often explains it. If there is overall demand among buyers for a thousand bales of cotton and only one hundred bales available from sellers, then the price remains strong and competition among sellers is at a minimum. But the opposite case with an opposite result is much more frequent: more commodities than there is demand for, resulting in a competition to sell for cheap.
How then, is the price determined in the midst of this? What is the standard or benchmark over which a seller must exchange their product in order to make a profit? That benchmark is determined by how much has been spent to make that product. The price spent on commodities -- raw materials, machinery, labor-power -- in order to make the finished commodity. If a shortage of some kind causes the price of a commodity to go up, then more capital will be poured into the manufacture of that commodity in order to maximize profit until things equalize. Same if a glut causes the price to go below the cost of production: capital will flee the manufacture of said product. But at any given time, it is not just one commodity whose price is fluctuating due to higher or lower supply in relation to demand. The price of this commodity may hinge on another product whose cost of production goes up or down, thereby impacting the cost of the former commodity.
By what are wages determined? If labor-power is a commodity then therefore it follows that the amount spent to produce it. Labor-power is "produced" by paying enough to get the worker through the door the next morning. "Thus," writes Marx, "the cost of production of simple labour-power amounts to the cost of the existence and propagation of the worker." Plenty receive less, however, insofar as capital is able to get away with it viz a viz lower expectations from workers themselves. And if there is a surplus of available labor-power on the market (say through a high unemployment rate)then employers are able to demand they pay less. The average of the minimum it takes to get workers through the door next day declines.
The nature and growth of capital: Marx insists that capital is a sum of commodities, of exchange values and of social magnitudes. If a similar commodity can be switched out for another with the same exchange value, then the nature of capital itself has not changed. Any product that can be exchanged for another is by its nature a commodity, and therefore any commodity is itself a sum of the smaller component commodities which had to exchange their way toward the total now being exchanged, with exchange values and their increase following in lock-step. Marx uses the example of a sheet of paper worth one penny, which is worth a hundred hundredths of a penny in terms of exchange value.
The adding up of these commodities, their transformation from component parts into a whole and therefore of a greater exchange value, is reliant upon labor. The assemblage of commodities and therefore multiplication of exchange value depends upon some living labor working on it and transforming it.
Relation of wage labour to capital: When the worker sells his labor-power, he gets wages that procure his means of subsistence. The capitalist in return for what he pays the worker gets that labor-power for a certain amount of time. But while the fruits of this labor-power serve to reproduce capital itself, the means of subsistence that the worker receives are lost as soon as they are consumed. An employer who pays his worker one shilling and gets two shillings back for the value produced by the worker has fruitfully reproduced the one shilling he spent. Meanwhile the worker spends the shilling and after has consumed what he buys for it has lost the value of the shilling forever. He cannot get another shilling unless he spends more time selling his labor-power. Capital, therefore, can only reproduce and multiply itself through the exertion of labor-power.
Marx illustrates the symbiotic nature of this relationship. If capital grows then so does the demand for labor-power; the price of wages goes up. But the amount that this new increase in labor-power produces itself continues to grow by a faster rate because of the differential laid out above. Therefore, even if the ability to buy more goods has increased for the worker, that of the capitalist has increased proportionately much more. Society as a whole has become richer, but the capitalist takes much more of this increase than does the worker. Further chaos could ensue in that there may be a glut of one or another commodity on the market, making the buying power of the worker's wages decline. Real wages are what a worker procures in terms of commodities with his wages; relative wages are determined in comparison to the overall wealth produced by his labor. It is a tendency in capitalism for the worker's relative wages to decline over time.
The general law that determines the rise and fall of wages and profits: If labor-power is one of the many commodities that goes into the assembly of a larger commodity, and if the payment for it comes out of what the employer pays for all those earlier commodities, and if the employer must sell the commodity at a rate that exploits the labor-power in order to profit, what is the relationship between wage and profit?
Marx puts forth that they operate in inverse proportion to one another. If the price of subsistence falls but and wages fall but not as much, the worker is gaining more for his lowered wages in proportion, but the capitalist is gaining even more. Mostly because he is now paying less on more than one front. Provided there isn't a glut of whatever commodity he is selling on the market, he is turning a larger profit. Profit increases as wages fall, and vice versa.
There are other ways to increase profit, for example bringing in more efficient machinery that enable a capitalist to meet demand at a faster pace and therefore profit more. But this too requires the labor of others, and though the worker's absolute wages haven't fallen, he isn't sharing in the higher profits. His relative wages have fallen.
It must be pointed out, however, that improvements to production, because they also decrease the cost of production, ultimately decrease the exchange value of the commodities. This is an odd kind of equalization that takes place in the ranks of capitalists, but take place it does. This describes the tendency for the rate of profit to decline.
The interests of capital and wage-labour are diametrically opposed -- effect of growth of productive capital on labor: Keeping the above in mind, it must also be remembered that capital's drive is perpetually toward growth. When a new piece of machinery enters into an industry that makes it possible to manufacture more and more of the same product for the same price, every competitor then is compelled to revolutionize their production in a similar way. This is yet another supporting fact toward the argument that workers' relative wages tend to drop.
Again, because the drive is toward constant growth, the subsequent reproduction and growth of the working class means only the reproduction and growth of its on exploitation. Capitalists, in order to drive competitors "off the field," must sell cheaper and cheaper (hoping that sheer volume makes up for lower prices) and therefore must cheapen and streamline the process of production. The contradiction is that even as they've introduced a new machine that streamlines production, that new machine itself requires a further division of labor, more workers. There is both more efficiency and less at the same time.
Effect of capitalist competition on the capitalist class, the middle class, and the working class: This section essentially serves as a recap. Because capitalists are forced to always be innovating their means of production, these innovations inevitably become the new normal in any sector of industry. In turn, labor is further divided and redivided, the process of production simultaneously becomes more complex and more efficient. Yet even as this happens and even as the overall wealth of society grows, the relative wage of the worker -- that which is spent to buy the worker's labor-power -- declines, even if their absolute wage grows. Given that it is the larger producer who is able to get more out onto the market quicker, the middle class (smaller businesses in particular) is constantly squeezed, thrust into the ranks of the working class if they can't compete on the scale of large capital.