One great blooming, buzzing confusion." That's how William James, writing more than a century ago, described the inner world of infants. Babies, unaware of the objects and people outside their bodies, see a kaleidoscope of shimmering pixels, he supposed. The famous Swiss psychologist Jean Piaget agreed: not until they are two years old do children fully appreciate that the world contains things that behave in predictable ways.
Nowadays every psychology student is taught that James and Piaget were wrong. From their earliest months, in fact, children interpret the world as a real and predictable place. It's the parents of an infant...