What are Marx's ideas on the fetishization of commodity? Specifically, I am interested in use value and exchange value; how does the commodity own its exchange value?
To answer the specific question first, take this analogy. How does an apple own its 'red'? It obviously doesn't, in some sense. All apples are black in the dark. No object has exchange value outside the context of a specific market. Yet in different contexts, beside bananas, say, rather than pomegranates, some apples are more red, and some are less red. And all commodities get prices through competitive comparison. The ephemeral quality is something Marx is trying to mark out as illusion, so we will question it. But is an apply any less red, once you realize that it is the context and the perceiver who declare it red?
The basic summary answer for the overall question is 'that it exists' which all other forms of economics find a problematic assertion.
A fetish is an attribute of the consumer that imputes extra value to something when and only when it takes a specific form or is represented in a specific way.
To go for the obvious sexual analogy, a sexual fetish is something that imputes extra attractiveness to a given trait (often so much that without the additional trait sex is compromised or seen as valueless).
There are obviously things that are sexually fetishized, in a way unrelated to their evolutionary usefulness, such as uniforms, amputations, shaved heads or other very strikingly non-sexual aspects of a person that must logically add sexual value only because of psychological projections.
There are other places where this is far less applicable as a notion. Someone who attributes higher sexual value to those with certain body hair patterns, can be seen as having a fetish for them. But there is an argument that body hair on a man simply is attractive, to different degrees, positive or negative, to anyone attracted to men as an aspect of secondary sexual traits that are just biological markers of genetic qualities.
Mainline economics puts price firmly in the second camp. Price is something that objects acquire in a market, whether or not it correctly represents utility. And having price can make something valuable to the market as a way of holding value. Gold has very limited direct utility, but maintains its price. (In fact when gold holds direct utility, as in electronics, it is sometimes subsidized for sale below market to remove its secondary value as a marker for price references.)
Marx would claim that almost the entire value of gold is added by fetishism and that the utility of the gold is more real. Then he (mistakenly in my interpretation) imputes the utility to its use-value: its cost and expected deployment in later costs.
(The most straightforward way to mock all attempts to tie use-value back to labor-value is that a link here implies the value of a good meal after it is digested should depend upon the work involved in cooking it, whereas all fertilizer is pretty much equal in utility.)
From that point of view, the market itself is simply a fetish-driven competition between addicts to the same fetish. The real value of things inheres in its utility, or some objective balance of its different levels of utility to different individuals.
I think, in a direction parallel to Marshal McLuhan, that there is a middle path here. The market is not just a mechanism, but also a 'medium', which is impressed with the standards of all the processes that affect it. For example want the expensive goods not the cheap ones, sometimes because they are simply better, and sometimes because we are in the thrall of the market as a medium of indoctrination which teaches us to behave in certain ways.
(This action of the market as medium is more obvious to me when we want the cheap ones even if the expensive ones really are very much better. 'Saving' money, especially on food, is a kind of entertainment provided by the market as a communication medium -- a sort of poor-woman's gambling. We go to McDonald's because a real restaurant is presumed to be pretentious and wasteful. Then we buy too much cheap food, eat it fast and over time we get insulin resistance. In that way we objectively fail to use most of our food for either enjoyment or energy.)
But that does not mean that the whole thing is an illusion, or even most of it.
The commodity is the central concept of Marxist theory. He describes it as the counterpart in economics of the "cell" in biology, and he opens Capital almost like a detective story tracing the origins of the commodity and its secrets of "surplus value."
Marx's theory of value is rather difficult and liable to various interpretations. Briefly, he developed the classical labor theory of value as originated by Smith, Ricardo, and others. All value derives from labor, but the capitalist classes receive their profit or "surplus value" by means of state-backed ownership, either of land, money capital, or the industrial "means of production."
The commodity combines "use value" (whatever it is used for) and "exchange value" (its relative value as measured and represented by money). But the two are arbitrarily related and the determining role is usually the "exchange value." To undergo the process of evaluation the commodity (C) must be produced from money capital (M) then transformed back into money capital plus surplus value (M'). So there is a continuous process of M-C-M' as well as C-M-C or, in finance, M-M'.
What is the commodity? Anything produced for exchange, usually on a mass scale through division of labor. A historical prerequisite for the system is the commodification of agriculture. This not only produces a mass market in agricultural commodities, it ensures that farmers cannot produce a balanced subsistence crop, and thus become utterly dependent for food on the market and bank loans.Many are then driven int to the labor market, or the "commodification" of labor. Likewise all labor becomes dependent on (M) and the totality of the commodity system.
It is important to note the almost everything in modern economy has a ghostly duality as "what it is" and how it is "represented in exchange" as a commodity. Labor is a commodity, industrial machinery is a commodity, education is a commodity, wheat is commodity, space is a commodity, health is a commodity, images are a commodity, etc. The entire system operates like a vast material language, with the numerical "value form" of "money" acting as the "symbolic" universal commodity.
Though commodification could be a historically brutal process (e.g. global commodification of cotton), Marx was not suggesting there was anything inherently evil about commodities per se, and assumed that socialism could only arise out of a complex division of labor and global commodification. His concern, among many, was tracing the origins of "surplus value" and analyzing the class structure and regular "crises" that characterize capitalism.
Now, the "fetish" of the commodity. The fetish is a material object assumed to harbor the power of a spirit or god, and actually taken as a substitute for the god itself. Similarly, the commodity exerts a deluding power. The vast network of social relations and value exchanges materialized in the commodity is taken to be a property of the commodity itself. This "invisible power" of global labor seems to radiate from the commodity in the form of social status or desire. We no longer see the commodity as the serial instantiation of a moving process, but as an object with a special property.
This concept has been developed in many different ways by a very large body of theory, reaching from classical economics to "culture industry" and "theory of the spectacle." The commodity is not an object, it is the fossilized imprint of a social relation and historical process.