How many senses does a human being have?

At least nine.

The five senses we all know about—sight, hearing, taste, smell, and touch—were first listed by Aristotle, who, while brilliant, often got things wrong. (For example, he taught that we thought with our hearts, that bees were created by the rotting carcasses of bulls, and that flies only had four legs.)

There are four more commonly agreed senses:

1. Thermoception, the sense of heat (or its absence)
2. Equilibrioception—our sense of balance—which is determined by the fluid-containing cavities in the inner ear.
3. Nocieption, the perception of pain from the skin, joints, and body organs. Oddly, this does not include the brain, which has no pain receptors at all. Headaches, regardless of the way it seems, don’t come from inside the brain.
4. Proprioception, or “body awareness.” This is the unconscious knowledge of where our body parts are without being able to see or fell them. For example, close your eyes and waggle your foot in the air. You still know where it is in relation to you.

Every self-respecting neurologist has their own opinion about whether there are more than these nine. Some argue that there are up to twenty-one. What about hunger? Or thirst? The sense of depth, or the sense of meaning, or language? Or the endlessly intriguing subject of synaesthesia, where senses collide and combine so that music can be perceived in color?