You recognize when you know something for certain, right? You "know" the sky is blue, or that the traffic light had turned green, or where you were on the morning of September 11, 2001--you know these things, well, because you just do.

In On Being Certain, neurologist Robert Burton shows that feeling certain--feeling that we know something--- is a mental sensation, rather than evidence of fact. An increasing body of evidence suggests that feelings such as certainty stem from primitive areas of the brain and are independent of active, conscious reflection and reasoning. In...