What is an emotion?

In 1884, William James, the American psychologist, famously posed the question: what is an emotion? After more than a century of scientific inquiry, however, emotions remain essentially contested concepts: scientists disagree on how they should be defined, on where to draw the boundaries for what counts as an emotion and what does not, on whether conscious experiences are central or epiphenomenal, and so on. Such disputes have sown great discord among scientists, leaving the field in perpetual upheaval, and without a unified framework for guiding scientific inquiry and accumulating knowledge. What follows is a dialogue between two neuroscientists who study emotions in humans: Ralph Adolphs (The Neuroscience of Emotion: A New Synthesis) and Lisa Feldman Barrett (How Emotions Are Made: The Secret Life of the Brain). Adolphs and Barrett agree that commonsense notions about emotion do not provide a solid ground on which to build a mature science of emotion. But they take very different scientific approaches, disagreeing on the most fundamental assumptions of what emotions are and how they work. We hope that this dialogue, moderated and edited by the theoretical physicist and noted science writer Leonard Mlodinow (Subliminal: How Your Unconscious Mind Rules Your Behavior; Elastic: Flexible Thinking in a Constantly Changing World), clarifies some of the key points of debate that may help with an eventual solution.