https://cla.purdue.edu/academic/english/theory/marxism/terms/termsmainframe.html#:~:text=Use%2DValue%20vs.-,Exchange%2DValue%3A,exchange%20value%20of%20the%20commodity.
Use-Value vs. Exchange-Value:The usefulness of a commodity vs. the exchange equivalent by which the commodity is compared to other objects on the market.Marx distinguishes between the use-value and the exchange value of the commodity. Use-value is inextricably tied to "the physical properties of the commodity" (126); that is, the material uses to which the object can actually be put, the human needs it fulfills. In the exchange of goods on the capitalist market, however, exchange-value dominates: two commodities can be exchanged on the open market because they are always being compared to a third term that functions as their "universal equivalent," a function that is eventually taken over by money. Exchange-value must always be distinguished from use-value, because "the exchange relation of commodities is characterized precisely by its abstraction from their use-values" (127). In capital, money takes the form of that equivalence; however, money in fact hides the real equivalent behind the exchange: labor. The more labor it takes to produce a product, the greater its value. Marx therefore concludes that "As exchange-values, all commodities are merely definite quantities of congealed labour-time" (130).
The epistemological and scientific foundation of classical political economy was the “labor theory of value” (LTV). Perhaps a more fitting description is the “labor law of value.”
The LTV predicts that the prices of commodities vary proportionally with their labor-content. If a commodity contains “more labor” than another, then in all probability the first will have a higher price. The LTV makes substantial law-like claims and is not a moral proposition.
Marx did not discover the LTV. However, he did make specific contributions to the theory, including, but not limited to, the hypothesis that labor is only represented as exchange value in societies with private ownership and atomized production for exchange, the distinction between labor and labor-power, and the concept of surplus value as functionally prior to its division between profit, interest, and rent.
Weston’s arguments were based on the acceptance of the theory of a wages fund – that is, a fixed amount of capital from which capitalists pay the wages of workers. The implication of this theory is that attempts, by the workers, to increase money wages will be ineffectual because capitalists will respond, either by raising the prices of necessities (thereby bringing real wages back to their previous level) or by reducing the number of workers employed. Hence, the theory was a weapon in the hands of the bourgeoisie in their efforts to resist the economic struggles of the proletariat; and, of course, if workers were not to participate in an economic struggle, they would not understand the need for a political as well as an economic struggle to overthrow capitalism. In short, the implication of this theory, which Marx understood well, was that the class of wage-labourers should be subservient to the class of capitalists. It was for this reason that Marx felt compelled to rebut Weston’s claims and that he argued in support of the economic struggle of the workers. However, Marx explained that this type of struggle is a means to an economic and a political end: the abolition of capitalism and the rule of the working class.