What explains such passionate philosophical disagreement between the Occupy Wall Street movement and the Tea Party? The seemingly insurmountable divide between left and right is perhaps most clearly understood by their respective concepts of human nature.

As understood by our Founders, human nature is innate. In the words of the Declaration of Independence, individuals are “endowed by their creator” with “natural rights,” among which are life, liberty, and the pursuit of happiness. Beyond that, individuals are born with different faculties and talents. Government should allow individuals to freely cultivate these traits.

So, how, then, did the Founders determine what constituted a “right”? Thomas West defines a right as “a claim that a person may rightfully make against someone who would deprive him of what is his own.” If I take the sweatshirt of my neighbor, my neighbor may rightfully make a claim against me, as he has the right to own his sweatshirt.

Importantly, every right corresponds with an equal duty: An individual’s right to liberty means that he or she has a duty to respect everyone else’s right to liberty.

John Dewey, a philosopher and pioneer of early progressive thought during the late 19th and early 20th century, turned the above concept of human nature on its head. Dewey believed that individual talents—the things our Founders and modern-day conservatives say humans are born with—are created by societal conditioning. He wrote that behavior, or habits, are “forced upon us,” adding that “social arrangements…are means of creating individuals.… Individuality in a social and moral sense is something to be wrought out.… These are not gifts, but achievements.” In other words, human beings are nothing on their own. Society—government—must create the individual.

Modern day left-wing philosophers, such as Richard Rorty and Peter Singer, echo Dewey. Rorty has written that “there is no such thing as human nature, for human beings make themselves up as they go along.”

This progressive line of thinking has serious implications. If individuals are not born with innate faculties—if society conditions them, as progressives argue—then what is there to prevent rights from expanding to whatever we as a society determine is necessary to create those faculties? Even Dewey himself made this point: “The state has the responsibility for creating institutions under which individuals can effectively realize the potentialities that are theirs.” Hence the left’s clarion calls for universal (meaning government-provided) health insurance, education, housing, transportation, food, and more.

This understanding of rights goes beyond the natural rights to life, liberty, and the pursuit of happiness proposed by the founders. If I have a right to health care, that means someone else, by definition, has the duty to provide me with it. But in forcing someone to provide me health care, I’m taking away his liberty.

One’s understanding of human nature will likely determine whether he’s conservative or liberal. At a time when our country is deeply divided, understanding the difference between the left’s and right’s concept of human nature has never been more important.