All this is the wrong context for the MBTI, though. The idea that human beings can be sorted into psychological types is ancient, of course. In the Hippocratic tradition, people could be categorized as innately sanguine, choleric, melancholic, or phlegmatic. (For melancholics, white wine was prescribed, to counteract the black bile.) In nineteenth-century Europe and America, phrenology was used to interpret character.

Systematic personality testing, though, is a twentieth-century thing. Annie Murphy Paul considers the Rorschach test, which was created in 1921, the first such device. In the case of the MBTI, three of the four binaries that the test uses were derived from Carl Jung’s book “Psychological Types,” also published in 1921. (Briggs had developed her own categories, but after reading Jung’s book she swapped out her terms for his. She also seems to have developed a long-distance crush and become a kind of Jung groupie.) The E.T.S. opened in 1947. By then, there were hundreds of personality tests on the market and hundreds of psychology consulting firms in business to administer them. According to Whyte, by 1952 a third of American companies were using personality tests.

But most of them were not using the MBTI. And that is because—as the E.T.S. finally concluded after pouring a lot of money into it—the MBTI is not a scientific instrument. Paul lists some of the criticisms of it made by the testing experts. More than half the people who take it a second time get a different score. Even the test-makers thought that it didn’t work for everyone. (As Myers put it: “The type differences show principally in the more intelligent and highly developed half of the population.”) And, in the aggregate, the results are insufficiently bimodal—that is, most test-takers fall between the binaries, neither extroverted nor introverted (as, after all, one would expect).

Most significant, the test is entirely self-reported. If you say you are extroverted, that is what the indicator believes. The system leaves no room for one of the most basic human capacities, the capacity for self-deception. Even the parlor game in which people characterize their friends as horses, birds, or muffins allows for false consciousness—for birds who think they are horses, or muffins who think they are birds (as most muffins do).

We might assume that the MBTI has workplace payoffs, since businesses apparently continue to pay for it. McKinsey, the corporate consulting firm, is said to use it in its own operations. But Paul, who is as skeptical as Emre, says that “there is scant evidence that MBTI results are useful in determining managerial effectiveness, helping to build teams, providing career counseling, enhancing insight into self or others, or any other of the myriad uses for which it is promoted.”

And it’s not easy to see how the different types correlate with different tasks. Here is how ENFPs (that is, people who are extroverted, intuitive, feeling, and perceiving) are described on the test’s official Web site,

Enthusiastic innovators, always seeing new possibilities in the world around them. Their world is full of possible projects or interests they want to pursue. Imaginative, high spirited, and ingenious, they are often able to do almost anything that interests them. They are confident, spontaneous, and flexible, and often rely on their ability to improvise.

They value home, family, friendships, creativity, and learning.

Here is a description of a personality type found on a different Web site:

Shy and quiet, but on the other hand they can be eccentric and energetic. However, in both cases, they are deep thinkers and highly intellectual people who love helping others. They are able to see without prejudice, on both sides, which makes them people who can easily solve problems. Although they can easily adapt to the energy that surrounds them, they have a deep need to be some time alone and away from everything, in order to restore power. They look at the world as a place full of possibilities.

That one is from It describes Aquarians.