In the First Treatise on Government (1689) Locke argued against English political theorist Robert Filmer, who claimed that kings, in a direct descent from Adam, had divine rights. Locke pointed out that it was impossible to trace such a direct descent with any accuracy, that human beings had female as well as male parents, and that political power was fundamentally different from patriarchal power.

In the Second Treatise on Government (1689), he identified natural law as God’s laws for man, which included the command that man labor for his living. God had given the earth and everything on it to all mankind. Locke therefore asked how it came to be that there was private property, which was necessary to make use of the fruits of the earth. His answer was that whatever an individual mixes his labor with he comes to own. (Locke used the term “mixes labor with” for labor, in cases where we today would say “works on.”)