The article discusses Marx's theory of value, which argues that the value of a commodity is determined by social relations between producers, not individual preferences. Value takes different forms depending on the stage of economic history, with capitalism being the most developed form. Exchange value is how value is expressed through labor. Marx builds on David Ricardo's labor theory of value, addressing issues like relative and absolute value. Challenges to Marx's theory include the role of demand in determining labor value and the relevance of transforming labor values into production prices. Time plays a crucial role in determining interest-bearing capital, and Adam Smith's distinction between productive and unproductive labor is important in understanding value as a social relation.