“Consciousness” refers to any subjective experience — the delectable taste of Nutella, the sharp sting of an infected tooth, the slow passage of time when bored, the sense of vitality and anxiety just before a competitive event. In the words of the philosopher Thomas Nagel, consciousness exists in a human or other subject whenever “there is something it is like to be that organism.” The concept has inspired countless philosophical theories since antiquity and much laboratory work over the past century, but it has also given rise to many misunderstandings. Published in the Washington Post in July 2019.