One may wonder how educators got so confused by Gardner’s theory. Why do they believe that intelligences are interchangeable or that all intelligences should be taught? The answer is traceable to the same thing that made the theory so successful: the naming of various abilities as intelligences.
Why, indeed, are we referring to musical, athletic, and interpersonal skills as intelligences?
Why indeed? After all, the essay concludes:
In the end, Gardner’s theory is simply not all that helpful. For scientists, the theory of the mind is almost certainly incorrect. For educators, the daring applications forwarded by others in Gardner’s name (and of which he apparently disapproves) are unlikely to help students. Gardner’s applications are relatively uncontroversial, although hard data on their effects are lacking. The fact that the theory is an inaccurate description of the mind makes it likely that the more closely an application draws on the theory, the less likely the application is to be effective. All in all, educators would likely do well to turn their time and attention elsewhere.
There's no good way to learn trigonometry except to do trigonometry. To try to teach it emphasizing each of the eight so-called intelligences would be a disservice to the student.