A concise and influential essay examining the nature of emotion and its relationship to bodily response.

In  this foundational text, William James advances the argument that  emotion is not the cause of physical reaction, but its consequence.  Rather than trembling because we are afraid, James proposes that we feel fear because we tremble. This reversal of common assumption reshaped psychological inquiry and helped establish modern theories of affect and  physiological response. 

Originally published in  1884, the essay became central to what is now known as the James-Lange theory of emotion. Its clarity and argumentative precision make it one of the most accessible entry points into James's broader philosophical and psychological system. Within the William James cluster, this work stands alongside The Varieties of Religious Experience, The Meaning of Truth, and Essays in Radical Empiricism as a key articulation of his empirical method applied to human consciousness.

Presented here in its complete form, What Is an Emotion? remains essential reading in the history of psychology and philosophy of mind.