What Is Consciousness?

The most intractable question in modern neuroscience and philosophy of the mind is often phrased "What is consciousness?" The problem has been summed up nicely by philosopher David Chalmers as what he calls the Hard Problem of consciousness: How is it that we are subjects, and not just objects? Chalmers contrasts this hard question with what he calls the Easy Problem of consciousness: What are the neurobiological substrates underlying such things as wakefulness, alertness, attention, arousal...