Irregular verbs! The very thought is enough to give anyone who has struggled with them a headache. In Words and Rules: The Ingredients of Language, MIT professor and evolutionary psychologist Steven Pinker has taken that scourge of language students and used them ingeniously to throw light on how our minds work and languages evolve.

Pinker, a Montreal native whose wit and good looks have made him something of a scientific superstar, has written two other books for the intelligent layperson: The Language Instinct: How the Mind Creates Language (1994) and How the Mind Works (1998). The first explained current scientific thinking on why and how we speak. It argued that humans who could speak had an advantage in the evolutionary sweepstakes. The second explored other characteristics that appear to have been shaped by natural selection: falling in love, smiling, and liking sweet things, to name only a few.

Readers looking for similar evolutionary psychology may be disappointed by this third book. While it is well written and entertaining, it sticks closely to one particular kind of research: why all languages have verbs with regular and irregular past tenses, and how people choose the right conjugation without hesitation. The research indicates that we use one part of our brains when we apply seemingly innate linguistic rules to produce the past participle of a regular verb. We use another, however, when we dredge up an irregular verb from where it has been stored with others.

Pinker is clearly fascinated by the linguistic gymnastics all of us do, but he also provides answers to critics who say that evolutionary psychology is not science, but a bunch of just-so stories, explanations of why we are the way we are with little science behind them. But, he writes, the past tense is the one place where deep philosophic questions about empiricism and rationalism – how humans think – “may be tested and compared on a single rich set of data, just like ordinary scientific hypotheses.”