I once took some education classes, and heard the unpleasant aphorism, “There are those who do, and those who teach, and those who teach teachers to teach.” The implication was that each group was less valuable. Perhaps no one who has had an excellent teacher would think this.
I was talking with a friend over the weekend about teaching, and agreed that teaching seems to be something that some people can do, and that that the skill seems to be more or less separable from the subject matter. (My friend is a skilled raconteur, and has taught on such disparate things as running a restaurant, singing in parts, mold removal and the Bible). If you can teach, you can teach anything you yourself are willing to learn.
It seems to me that writing is another “separable skill,” and a good writer can write about almost anything — think of John McPhee writing about oranges, canoes, geology and fish; or Michael Lewis writing about football, baseball, the technology of markets, or disease; or Tracy Kidder writing about Haiti, contracting, computers and Burundi. This is strongly true of writers of nonfiction, though I concede that not all nonfiction writers can make the leap into fiction, and poetry is another thing entirely.
We hear of people who are “book smart” and the ability to learn from books may be its own separable skill, but not all separable skills are intellectual — we all know people who are sufficiently athletic that they would be picked for any team even in a sport they have never played before. Some people have mechanical ability as a separable skill. Musical aptitude may be a separable skill.
Are there others?