Some animals have gotten to be so fancy that they simulate a course of action before taking even a tentative first step. The chess master, who looks a half-dozen moves ahead, is a prime example — as is the army general or poker player who thinks through bluff and counterbluff before acting. These are only extreme examples of how to make and compare alternative plans, but they illustrate the same sort of process that we all go through when simply contemplating the leftovers in the refrigerator, trying to figure out a combination that will avoid another trip to the grocery store.

Many animals look ahead in a limited way, predicting when winter is coming. But that requires only the simplest of nighttime-length-sensitive hormonal mechanisms, not even a brain. It's a novel course of action, one that neither you nor any of your ancestors has done before, that is the difficult part.

And not even that is hard, if you have the time to grope around. A goal, and some feedback about progress, suffices for many novel situations. But if I have to pick up a cup of uncertain weight and bring it to my lips in less than a quarter of a second, feedback doesn't have time to help — and so I'll hit my nose if I haven't made the perfect plan in advance. Personally, I think that the extensive planning needed for such ballistic movements as throwing, hammering, kicking, clubbing, and spitting has been very important in the ice age evolution of the human brain — and that we use the same neural machinery for planning what to speak next, or listen to music, or to plan a dinner of leftovers.

Creativity — indeed, the whole high end of intelligence and consciousness — involves playing mental games that shape up quality. Humans can simulate future courses of action and weed out the nonsense off-line. As the philosopher Karl Popper has said, this "permits our hypotheses to die in our stead."

What sort of mental machinery might it take to do this mental feat? I suggest, in How Brains Think (Science Masters), that our brains perform a vastly speeded-up version of the same Darwinian process used in evolving new plant and animal species, the same process seen in the immune response in the days and weeks following a flu shot. In The Cerebral Code (MIT Press), I discuss the cerebral circuitry that does the job.

By borrowing the mental structures for syntax to judge other combinations of possible actions, we can extend our plan-ahead abilities and our intelligence. To some extent, this is done by talking silently to ourselves, making narratives out of what might happen next, and then applying syntax-like rules of combination to rate a candidate scenario as dangerous nonsense, mere nonsense, possible, likely, or logical. But our intelligent guessing is not limited to language-like constructs; indeed, we may shout "Eureka!" when a set of mental relationships clicks into place, yet have trouble expressing this understanding verbally for weeks thereafter. What is it about human brains that allows us to be so good at guessing complicated relationships?

We create sequences when we speak a sentence that we've never spoken before or improvise at jazz or plan a career. We invent dance steps. Even as four-year-olds, we can play roles, achieving a level of abstraction (that "willing suspension of disbelief") not seen in even the smartest apes. Many of our beyond-the-apes behaviors involve novel strings of behaviors, often compounded: phonemes chunked into words, words into word phrases, and (as in this paragraph) word phrases into complicated sentences with nested ideas.

Rules for made-up games illustrate the memory aspect of this novelty: we must judge possible moves against serial-order rules, for example, in solitaire where you must alternate colors as you place cards in descending order. Preschool children will even make up such arbitrary rules, and then judge possible actions against them. We abandon many of the possible moves that we consider in a card game once we check them out against our serial-order memories of the rules. In shaping up a novel sentence to speak, we are checking our candidate word strings against overlearned ordering rules that we call syntax and grammar. Our plan-ahead abilities gradually develop from childhood narratives and are a major foundation for ethical choices, as we imagine a course of action, imagine its effects on others, and decide not to do it.

That's the mentality that chess illustrates so well. Humanity wouldn't be human (or humane) without it.

William H. Calvin is a theoretical neurophysiologist at the University of Washington in Seattle. He is the author of nine books, including The Cerebral Code, How Brains Think, The River that Flows Uphill, and, with the neurosurgeon George A. Ojemann, Conversations with Neil's Brain.

For a further discussion of these topics, visit William H. Calvin's Web site.