Every sentence we hear is instantly analyzed by an inner grammar; just as a prism refracts a beam of light, grammar divides a stream of sound, linking diverse strings of information to different domains of mind-memory, vision, emotions, intentions. In "The Prism of Grammar", Tom Roeper brings the abstract principles behind modern grammar to life by exploring the astonishing intricacies of child language. Adult expressions provide endless puzzles for the child to solve. The individual child's solutions ("Don't uncomfortable the cat" is one example) may amuse adults but they also reveal the complexity of language and the challenges of mastering it. The tiniest utterances, says Roeper, reflect the whole mind and engage the child's free will and sense of dignity. He offers numerous and novel "explorations"-many at the cutting edge of current work-that anyone can try, even in conversation around the dinner table. They elicit how the child confronts "recursion"-the heartbeat of...