There are between nine and twenty-one human senses, depending on who you ask, and how they define a sense. It is generally agreed that nine is the minimum. These are touch, taste, smell, sight, hearing, thermoception, nociception, equilibrioception, and proprioception. Hunger and thirst are also sometimes included. Generally, for something to qualify as a sense requires a free-standing sense organ associated with it. A sensory apparatus' primary source of information should be force data originating from outside the brain.

Thought or intuition is sometimes included as a sense, but this is incorrect. Human thoughts do not take data directly from reality, but rather from the confluence of sensory organs with which they are connected. Sometimes senses are perceived concurrently with each other, for example sounds that have colors associated with them. This phenomenon is called synesthesia, and is relatively rare, though often reported under the influence of hallucinogens or psychedelics.

Because the five Aristotlean senses of sight, hearing, taste, touch, and smell -- respectively vision, audition, gustation, tactitian, and olfaction -- are well-known, let's take a look at the less popular senses. Despite their infrequent mention, these other senses are very important to our survival and daily functioning.

Equilibrioception is our sense of balance, perceived by the position of fluids in the inner ear. It can be sent off kilter if one spins around in a circle too many times. Having a sensory faculty for the perception of balance is essential for any bipedal species.

Proprioception is the perception of one's body in space. Like equilibrioception, the data for this sensory faculty comes from within the body rather than from the environment. Proprioception is what a police officer tests when they pull you to the side of the road for suspicions of drunk driving.

Thermoception and nociception were once thought to be simple variations on touch, but they are not. Thermoception is the sensation of heat and nociception is the sensation of pain. Thermoception of external heat sources is quite distinct from the sensation of internal body temperature, which uses a different apparatus. Also, nociception has sometimes been categorized as three senses rather than one, because different receptors perceive pain on the skin, the joints and bones, and the body organs respectively.