Our usual rule of thumb for the presence of consciousness is to assess, based on superficial cues, how similar to ourselves something appears to be. Thus a dog is more conscious than a duck, which in turn is more conscious than a daffodil. But our intuitions about so many things—rom the motions of celestial objects to the likelihood of winning the lottery—are so often wrong that we are foolish to rely on them for something as important as the ultimate source of all joy and strife.

Famously, and ironically, the only thing of which we can be truly certain is the existence of our own subjective experience, and we see the physical world only through this dark glass. Yet the scientific method has proved a remarkable tool for clarifying our view and enabling us to develop an elaborate, apparently objective consensus about how the world works. Unfortunately, having provided us with an escape route from our own subjectivity, science leaves us almost completely impotent to probe the nature and origins of subjective experience itself. The truth is that we have no idea what things have consciousness, where it comes from, or even what it is. All we really know is how it feels.