How did Adam Smith and Karl Marx view human nature and define the purpose of the state?

Adam Smith and Karl Marx were both initially trained as philosophers, and then both went on to focus more on economics than philosophy. They were both certainly political philosophers, or if they wouldn’t describe themselves that way, at the very least they focused on theories of politics and economics. Smith’s magnum opus, An Inquiry into the Nature and Causes of the Wealth of Nations, or just The Wealth of Nations, indicates that there is a propensity in human nature toward a desire to barter or exchange goods and services for other goods or services as we need them. He casually asserts (without defending this statement, since it is not part of his main point) that this propensity has most likely been acquired with the advent of reason and written and spoken language. (Reason, by the way, is the apex of human achievement and our crowning glory, according to 18th and 19th century German Idealism philosophy. Human rationality continues to be seen as our defining characteristic to this day.) The desire to exchange one thing for something else that is more useful to us is, in Smith’s estimation, a part of our nature as humans. This desire also ends up serving us all pretty well, since it means that the baker can keep some bread for himself, and trade some bread for a coat, which means he doesn’t have to learn how to make his own coat or buy the materials to do so. That is to say, when we decide to barter what we have or can make for things that we don’t have, or can’t make, we have a natural division of labor.

Smith held that the role of the state was primarily to enforce contracts. Bartering entails a usually tacit contract, but much of society is based on more formal contracts as well. The role of the state is also to grant patents and copyrights and encourage new ideas and entrepreneurship.

Karl Marx certainly held a different idea of human nature and the purpose and role of the state than Adam Smith did, and wrote about some of his ideas in Das Kapital. He agreed with Smith’s basic ideas about the division of labor in capitalist society, but he also believed that at base, the source of capitalist profit was the exploitation of the working class. He held a somewhat complex “labor theory of value,” claiming that only human labor was variable capital whereas all other sources of profit were constant capital. This theory that surplus profit can only come from human labor doesn’t work out in reality, but one point that remains relevant is his criticism of the exploitation of the lower working classes.

Marx believed that capitalism is not based on any particular nature or propensity of humans, and that since it rested on the weary back of the working class, it would eventually fail. He also believed that the fall of capitalism would instigate the rise of communism, or a classless society, but what that would look like in reality when it came about was not something he felt anyone could predict, since it would be a product of our future history.