Think about pain. You can’t see it on a scan. Your doctor asks you to rate it from one to ten, and whole drug trials are built on your answer. Vision researchers ask people whether they can see a faint light. Consciousness research depends on people telling us what they experienced because there is no other way in. If subjective data were banned, large parts of medicine and psychology would shut down by lunchtime.

A few years ago, I caught the smell of a particular hand cream in a shop and was, for a moment, entirely somewhere else. Not remembering somewhere else. Somewhere else. My grandmother's kitchen, a specific afternoon, the quality of the light, a feeling in my body that I had not had in decades and that arrived whole, instantly, before I had time to think the word memory at all. I was not recalling the past. I was, in some sense I could not account for, back inside it.