When scientists began to study expertise, they first assumed that experts must be smarter or more talented than novices, but they quickly learned that the key difference between experts and novices is not mental power, but knowledge. Cognitive psychologists Michelene Chi, Marshall Farr, and Robert Glaser have defined an expert as somebody who has a great deal of highly organized domain-specific knowledge, where a domain is a network of knowledge, such as chess, mathematics, or music. For experts, knowledge has morphed from many pieces into a unified whole. An expert can start with any piece of knowledge and explain how it fits with every other piece. I always picture the way Sherlock Holmes could start with a soil stain and, through a chain of reasoning, solve the case.
Understanding other people's expertise can help you develop your own. Surprisingly, experts make mistakes, but experts catch and correct their mistakes faster than do novices. Experts take a long time to make sure they understand a problem. If you give an expert and a novice the same problem, the novice will immediately begin to try to solve it. The expert will reﬂect on the nature of the problem. From the outside, it will appear as if the expert is doing nothing and the novice is making progress. Once the expert understands the problem, she can solve it better and faster than can the novice.
Understanding expertise also helps you see where intuition comes in: it comes last. Experts do use intuition to solve problems, but it is a cultivated intuition resulting from at least 20,000 hours of on-task study. Intuition works as a guide only after experts have satu¬rated themselves with their field's knowledge. Herbert Simon described expertise as follows:
"Counts have been made of the number of "friends" that chess masters have: the numbers of different configurations of pieces on a chessboard that are old familiar acquaintances to them. The estimates come out, as an order of magnitude, around fifty thousand, roughly comparable to vocabulary estimates for native speakers. Intuition is the ability to recognize a friend and to retrieve from memory all the things you've learned about the friend in the years you've known him. And of course if you know a lot about the friend, you'll be able to make good judgments about him. Should you lend him money or not? Will you get it back if you do? If you know the friend well, you can say "yes" or "no" intuitively."
Nobel laureate Louis Alvarez provides an example of how to learn the language of a domain. Louis and his son, Walter, were the first scientists to suggest that an asteroid killed the dinosaurs. The clue was a dusting of iridium, an isotope that is rare on earth but common in asteroids. As soon as Alvarez saw it, he knew it was significant; but how did he know? Alvarez's biographer Richard Rhodes wrote that for years, Alvarez ran the only cyclotron in the world: "On a wall in the laboratory the young physicists put up a big board laid out with the periodic table, with hooks projecting from the boxes designating elements, and each time someone identified a new isotope, Luie labeled a wooden tag with the isotope's characteristics and hung the tag from the ap¬propriate hook. That's how he got to know isotopes so well. The knowledge he derived from those hard early years of work stayed with him like a vocabulary for the rest of his life." In short, you are an expert in your field when you know its vocabulary and grammar as well as you know that of your native language.
Chi, M., M. Farr, and R. Glaser. 1988. The Nature of Expertise. Hillsdale, NJ: Lawrence Erlbaum Associates.
Rhodes, R. 1995. How to Write: Advice and Reﬂections. New York: William Morrow and Company.
Simon, H. 1983. Reason in Human Affairs. Stanford, CA: Stanford University Press.