"Eureka: What makes coherence so important to us?"

When something is missing, it bothers us that things don't hang together. Consider: "Give him." In any language, that is a bothersome sentence. Something essential is missing, and it rings an alarm bell in our brains. We go in search of an implied "what" and try to guess what will make the words all hang together into a complete thought.

We ask questions in search of satisfying incompletes, again hoping to create some coherence. No other animal does such things. It even forms the basis of many of our recreations such as jigsaw and crossword puzzles, all those little eurekas along the way.

Guessing a hidden pattern fascinates us. It's part of our pleasure in complex ritual or listening to Bach, to be able to guess what comes next some of the time. It's boring when it is completely predictable, however; it's the search for how things all hang together that is so much fun. Of course, we make a lot of mistakes. Every other winter, I get fooled into thinking that a radio has been left on, somewhere in the house, and I go in search of it — only to realize that it was just the wind whistling around the house. My brain tried to make coherence out of chaos by trying out familiar word patterns on it.

Astrology, too, seems to make lots of things "all hang together." Often in science, we commit such initial errors but we are now fairly systematic about discovering and discarding them. We go on to find much better explanations for how things hang together. Finding coherence is one of our great pleasures. It would be nice to know what predisposes our brain to seek out hidden coherence.

For one thing, it might help illuminate the power of an idea — and with it, how fanaticism works.

Fundamentalist schemes that seem to make everything hang together can easily override civilization's prohibitions against murder. Inferring an enveloping coherence can create an "other" who is outside the bounds of "us." Because it seems so whole, so right, it may become okay to beat up on unbelievers — say, fans of an opposing football team, or of another religion.

For scientists and crossword fans, it's finding the coherence that is important. Then we move on. But many people, especially in the generation which follows its inventors, get trapped by a seemingly coherent worldview. Things get set in concrete; the coherent framework provides comfort, but it also creates dangerous us-and-them boundaries.

William Calvin is a theoretical neurobiologist at the University of Washington and author of How Brains Think.