If you’re good at finding the one right answer to life’s multiple-choice questions, you’re smart. But intelligence is what you need when contemplating the leftovers in the refrigerator, trying to figure out what might go with them. Or if trying to speak a sentence that you’ve never spoken before. As Jean Piaget used to say, intelligence is what you use when you don’t know what to do, when all the standard answers are inadequate.

—William H. Calvin, How Brains Think: Evolving Intelligence, Th...