“A use-value, or useful article, therefore, has value only because abstract human labour is objectified or materialized in it. How, then, is the magnitude of value to be measured? By means of the quantity of the "value-forming substance", the labour, contained in the article. This quantity is measured by its duration, and the labour-time is itself measured on the particular scale of hours, days etc.”

German philosopher and revolutionary socialist

Karl Marx was a German philosopher, journalist, political theorist, and revolutionary socialist of the 19th century. He is known for shaping modern socialist thought and for his analysis of capitalism and class struggle. He developed historical materialism, arguing that social change is driven by material conditions and conflict between classes. He also co-wrote The Communist Manifesto with Friedrich Engels and spent much of his work on a critique of political economy in Das Kapital. His ideas, later gathered under the name Marxism, became highly influential in politics, scholarship, and revolutionary movements.