The example Feynman gives comes from the most rudimentary source, a “first grade science textbook” which “begins in an unfortunate manner to teach science”: it shows its student a picture of a “windable toy dog,” then a picture of a real dog, then a motorbike. In each case the student is asked “What makes it move?” The answer, Feynman tells us “was in the teacher’s edition of the book… ‘energy makes it move.’” Few students would have intuited such an abstract concept, unless they had previously learned the word, which is all the lesson teaches them. The answer, Feynman points out, might as well have been “’God makes it move,’ or ‘Spirit makes it move,’ or, ‘Movability makes it move.’”
Instead, a good science lesson “should think about what an ordinary human being would answer.” Engaging with the concept of energy in ordinary language enables the student to explain it, and this, Feynman says, constitutes a test for “whether you have taught an idea or you have only taught a definition. Test it this way”:
Without using the new word which you have just learned, try to rephrase what you have just learned in your own language. Without using the word “energy,” tell me what you know now about the dog’s motion.
Feynman’s insistence on ordinary language recalls the statement attributed to Einstein about not really understanding something unless you can explain it to your grandmother. The method, Feynman says, guards against learning “a mystic formula for answering questions,” and Oxenham describes it as “a valuable way of testing ourselves on whether we have really learned something, or whether we just think we have learned something.”
It is equally useful for testing the claims of others. If someone cannot explain something in plain English, then we should question whether they really do themselves understand what they profess…. In the words of Feynman, “It is possible to follow form and call it science, but that is pseudoscience.”