Developmental psychologist Howard Gardner has dedicated his career to studying intelligence — specifically, his theory of multiple intelligences. According to Gardner, there is no such thing as a single form of measurable human intelligence, but something much closer to eight (and counting...). We spell them out below.

The terms "book smart" and "street smart" are no doubt familiar, but what about musical or even bodily intelligence? In a video published by Big Think, Professor Howard Gardner talks about the "eight intelligences that I’m very confident about and a few more that I’ve been thinking about."

Linguistic + Logical Intelligences

These first two forms of intelligence are the ones we know well, often measuring them using such methods as exams and standardized tests. We also use them to know whether a person can proficiently perform a task, such as writing an essay, solving a complex equation, or even speaking in complete and grammatically coherent sentences. Do well in both of these, Gardner says, and you consider yourself smart. "But," Gardner says, "if you ever walk out into Broadway or the highway or into the woods or into a farm, you then find out that other intelligences are at least this important."

Musical Intelligence

Gardner defines the third intelligence as, "the capacity to appreciate different kinds of musics, to produce the music by voice or by an instrument or to conduct music." For Gardner, musical talent is actually an intelligence because it involves being good with "tones and rhythms and timbres."

Spatial Intelligence

How well do you navigate a space? Spatial intelligence, as Gardner defines it, depends on how well you can orient yourself and get to where you want to go — whether it's a room, a road, a chessboard, or the open sea.

Bodily Kinesthetic Intelligence

Bodily kinesthetic intelligence, Gardner says, "comes in two flavors." The first, employed most readily by athletes and dancers, is "the ability to use your whole body to solve problems or to make things." The second also involves solving things, but only using parts of your body to do so. Think makers, tinkerers, designers, or builders.

Watch Professor Howard Gardner speak on the Eight Intelligences in full:

Interpersonal Intelligence

You might call this social smarts, or being socially adept, but as Gardner defines it, interpersonal intelligence is all about "how you understand other people, how you motivate them, how you lead them, how you work with them, how you cooperate with them." This form of intelligence is considered essential for any person who works with others, but it has a potentially unfavorable side as well. "Leaders hopefully have a lot of interpersonal intelligence," Gardner says, "but any intelligence can be used in a pernicious way, so the salesman that sells you something you don’t want for a price you don’t want to pay, he or she has got interpersonal intelligence."

Intrapersonal Intelligence

Intrapersonal intelligence is all about knowing and understanding yourself: How you tick, what you like, how you work, and your strengths, weaknesses, and proclivities. This form of intelligence (so far) may not be easy to quantify, but, as Gardner attests, it's vital. "Nowadays," Gardner says, "especially in developed society, people lead their own lives. We follow our own careers. We often switch careers. We don’t necessarily live at home as we get older. And if you don’t have a good understanding of yourself, you are in big trouble."

Naturalist Intelligence

The final form of intelligence (so far), naturalist intelligence is "the capacity to make important, relevant discriminations in the world of nature between one plant and another, between one animal and another. It’s the intelligence of Charles Darwin." But since many of us don't live in places where nature is still at center stage, we've adapted our naturalist brains to our modern lifestyles, allowing us to make discriminating choices about things such as how we dress, what we drive, or even what we choose to surround ourselves with.

(Teaching + Existential Intelligences)

These two forms of intelligence haven't formally been added to Gardner's list — yet. The first, called teaching or pedagogical intelligence, determines how successful you are at teaching other people. Surprisingly, this has less to do with knowledge or expertise and more to do with how well you can explain a subject, issue, or thing to someone else, regardless if that person is older or younger. Existential intelligence is "the intelligence of big questions." For Gardner, "Part of the human condition is to think about questions of existence."

So, is it worth concentrating on just one or two forms of intelligence (becoming experts), or is it worth it to cultivate multiple forms of intelligence, even if we might never gain full mastery in any of them?

According to Gardner:

if a parent came to me and said well should we supplement or should we accentuate, I would say well tell me what you would like your child to do. Or better let the child tell you what he or she wants to do rather than say well science says you should do one or the other. I think it's a question of values, not of science.

Howard Gardner, a developmental psychologist, is the John H. and Elisabeth A. Hobbs Professor of Cognition and Education at the Harvard Graduate School of Education. Gardner is also an Adjunct Professor of Psychology at Harvard University and Senior Director of Harvard Project Zero. Watch the video on the Eight Intelligences, published by Big Think.