David Hume’s A Treatise of Human Nature was first published in 1740. Although the book did not sell well on its release, it became one of the key texts of the Enlightenment. It was especially known for its argument that human knowledge is based on direct experience and observation—a school of philosophy known as empiricism—and that human behavior is not based on reason, but on emotions. Divided into three books, A Treatise of Human Nature explores Hume’s initial ideas about the processes of human understanding, the nature of emotions and passions, and the structures of human morality. Hume eventually returned to these topics, offering revised and expanded ideas in his works An Enquiry Concerning Human Understanding (1748) and An Enquiry Concerning the Principles of Morals (1751). Hume’s ideas influenced numerous philosophers during his own time and afterward, including Jean-Jacques Rousseau, Arthur Schopenhauer, and Karl Marx, amongst many others.

This guide uses the Penguin Classics edition.

Summary

Book 1 is titled “On The Understanding.” The focus is on the fundamentals of not just how people learn, but how they process the world around them and their own thoughts and attitudes. Hume argues that we develop ideas based on our impressions, which come out of our physical senses like sight and hearing. More complex ideas form out of the associations between different ideas and impressions. From these associations, Hume argues we develop all sorts of concepts, from imaginary creatures to belief in cause and effect. We ultimately cannot be absolutely certain in what we know about the world outside our own minds or have much trust even in cause and effect, but we can draw fairly reliable conclusions from repeated observation, not from abstract reasoning and logic.

In the next book, “Of The Passions,” Hume discusses how ideas lead into emotions, or what Hume calls “passions.” The passions likewise all originate from our experiences and ideas, specifically our sensations of pleasure or pain (which Hume also calls good or evil). The more vivid the ideas they are based on, the more powerful the passions. However, Hume argues we still have passions that apply to complete strangers and people we never met. Hume suggests that this too comes from how we associate ideas and impressions in our imagination, a force Hume labels “sympathy.” Also, Hume rejects the traditional Western idea that the emotions and reason are in conflict. Instead, reason “is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them” (462).

Finally, in the third book, “Of Morals,” Hume goes further, saying that our ideas of vice and virtue spring from our ideas and our passions. Our ideas of vice and virtue can be traced back to our ideas about our own self-interest and our social relations. Some morals, like justice and modesty, are even simply social inventions, created to protect people, the proper use of resources, and the agreements between people from destructive human tendencies like excessive self-interest. Overall, even complex and abstract ideas, such as our concepts of just government and of moral virtue, stem from our lived experiences.