Consciousness remains the deepest puzzle in human science. Even as we begin to understand how the brain processes information, we remain as far as ever from understanding why any of that processing should feel like anything from the inside.

That mystery is what drew me into consciousness research, and over time I came to think the puzzle was as much a moral one as a metaphysical one. Consciousness is what makes things matter. Pains that don’t hurt aren’t pains, and joy that goes unfelt isn’t joy. Without consciousness, paradise and torment may as well be the same thing.

This has real implications, most notably in our treatment of animals.…