Lenin: Classical political economy, before Marx, evolved in England, the most developed of the capitalist countries. Adam Smith and David Ricardo, by their investigations of the economic system, laid the foundations of the labour theory of value. Marx continued their work; he provided a proof of the theory and developed it consistently. He showed that the value of every commodity is determined by the quantity of socially necessary labour time spent on its production. https://wordsmith.social/protestation/quotes#quote4620