Science Fact:  The five senses bring the world into our awareness.  But who decided there were five senses, anyway?

Five Senses.  In Western culture many things we think we “know” often come from ancient Greece.  Sure enough, Aristotle, who has been called the “first genuine scientist,” enumerates the same five senses that we know: sight, hearing, smell, taste and touch.  Yet the Greeks were not fixed on the number five: Aristotle sometimes leaned toward four senses, taking taste to be merely a form of touch; and his teacher Plato instead rattled off an impressive list of at least eight senses: hearing, sight, smell, sense of heat and cold, pleasure, pain, desire, and fear.

Nevertheless, five senses are engrained in our thinking.  Perhaps because we can easily associate a physical structure (eye, ear, nose, tongue, hand) with each one.  Perhaps because five senses were a frequent theme in Medieval and Renaissance art.  Perhaps because the most casual search turns up mountains of hits on the subject of five senses, ranging from scientific discussions, to products and services, to metaphorical and poetic works.

Six Senses.  When people speak of a “sixth sense” it’s as if they are talking about a third eye, or a fourth dimension, or a fifth cardinal direction – it’s shorthand for some mysterious way of knowing things that we wouldn’t normally expect to know.  Advocates of extrasensory abilities such as telepathy would propose ESP as a sixth sense.  However, even before the ancient Greeks, Buddhism counted six senses by including the mind as a sense organ.  And the mind is about as mysterious as you can get!

Seven Senses.  As Charles South pointed out in a note to me, we don’t have to get esoteric to justify more than five senses.  Balance, the ability to sense and adjust to gravity and to perceive acceleration, is a fundamental sense throughout the animal kingdom.  After all, knowing which way is up and being able to stay on one’s feet is necessary to find food or a mate, and to avoid becoming some other creature’s lunch.

The other sense most often included in a basic seven is proprioception, the awareness of the position and configuration of our body parts.  This awareness greatly improves the efficiency with which we grasp objects or move our bodies.  The logo at the start of this post featuring seven senses comes from the Seven Senses Foundation in Australia, which is working to make city streets less of a racetrack for cars and more of a safe place for neighborly socializing.

Nine Senses.  Seven senses are not the last word in the count of our sensory organs.  We can also sense temperature (hot or cold), and pressure changes (as our ears pop when changing altitude).

Fourteen Senses.  The nine senses mentioned above (leaving out the exotic number sixes) all deal with things that happen and can be observed outside the body.  However, what about the senses that tell us what’s going on inside our bodies?  Senses such as hunger, thirst, pain and muscle tension.  Moreover, we are also sensitive to a variety of blood-borne chemicals that we experience in various ways: the “burn” of muscles after exercise; the dizziness or euphoria of less or more oxygen in the air we breathe; love and desire causing our heart to pound and hormones to flow; and no doubt others too.  If we sweep all these chemical senses into one, despite their differences in detail, we’re up to fourteen.

Eighteen Senses.  If we had to hobble around with merely fourteen senses, we could have a tough time getting along in the modern world.  There are more complex senses that we use every day, such as:
– Empathy, our ability to understand another person’s feeling and respond appropriately;
– Situation awareness, our knowledge of the threats or opportunities in our surroundings;
– Chronoception, our sensing of time intervals and the passage of time;
– Intuition, the way in which we process many layers of information to make decisions without always knowing how we got there.

Twenty-Five Senses.  Evidently, even without assistance from cell phones and night vision goggles, human beings have a tremendous number of faculties that we might call senses.  However, there are animals that perform amazing behavioral feats that when studied have revealed still more senses:
– Echolocation by bats, dolphins and a few other animals;
– Electroreception, the detection (and in some cases, generation) of electric fields by fish, sharks, rays, electric eels, dolphins, platypuses, echidnas and bees;
– Magnetoreception, the detection of magnetic fields by migratory birds, sea life (turtles, sharks, rays, lobsters), insects (including fruit flies and honeybees) and even bacteria;
– Other animal senses that have been studied include the detection of water pressure, water flow (sea currents), light polarization and skeletal strain.

Now that we have counted up twenty-five senses perhaps we should return to Plato and simply accept Socrates’ description of the senses as “innumerable”: (Dialogue: Theaetetus)
“…there is nothing but motion, which has two forms, one active and the other passive, both in endless number; and out of the union and friction of them there is generated a progeny endless in number, having two forms, sense and the object of sense, which are ever breaking forth and coming to the birth at the same moment. The senses are variously named hearing, seeing, smelling; there is the sense of heat, cold, pleasure, pain, desire, fear, and many more which have names, as well as innumerable others which are without them…”

Science Speculation:  An ancient adage about the senses proclaims, “in the land of the blind, the one-eyed man is king.”  So human gifts are indeed relative, but is it true that more or better senses will confer fame and fortune?  If the one-eyed man is not careful he may be lynched rather than crowned.

Many science fiction and fantasy stories posit a secret sense, a sixth sense of the esoteric type mentioned above.  The possessors of secret senses must hide their gifts or come into conflict with others.  A few classics that explore secret senses are Asimov’s Foundation and Empire, Heinlein’s Stranger in a Strange Land, Clarke’s Childhood’s End and Dick’s UBIK.

But if a secret sense or sixth sense is a sense that only the holder knows he has, then intuition is that same sense without self-knowledge.  Thus a seer with a sixth sense is only a short step away from the intuitive person, the lucky one who “accidentally” gets things right more often than anyone would expect.

The key difference between a secret sixth sense and intuition is that when we refer to intuition, we are talking about a sense that we believe is explainable by known physical principles: it’s just that the explanation is so complex that we haven’t figured it out yet.  And this brings us to writer Arthur C. Clarke’s famous “Third Law“: Any sufficiently advanced technology is indistinguishable from magic.

Intuition? Magic? Perhaps they are two different perspectives on the same thing: the last of the senses, the one whose explanation is always just beyond our grasp.

How many senses do you actually rely on, day-to-day?  If you could substantially improve any one sense, which one would it be?

Drawing Credit: Seven Senses Foundation logo, used with permission.  7 Senses Foundation in Australia is working to advance the idea of enhanced sensory living.  Their Street Day project encourages residents and designers to think about improving sensory engagement in our daily places and lives.