A bunch of my friends and I were sitting around the dinner table one night, and we got to talking about what is most important to know about science: What scientific concepts are absolutely essential for kids to know by the time they get out of school?

Someone suggested Isaac Newton's laws of motion, which seemed reasonable. You know the laws I mean, the ones having to do with vectors and forces and momentum and that sort of stuff. Come to think of it, I can't quite remember anything very specific about those laws now, although I know they're essential.

On second thought, how essential could they really be? True, you can't send a rocket to the moon without knowing them. But what about for nonscientist types like me? I seem to be getting along okay in my daily life without ever thinking of the laws of motion.

Someone else suggested the theory of evolution. Now there's a topic that comes up frequently in society at large. Surely it's important for people to know what that theory is about, so they can debate it intelligently!

We all started nodding and agreeing. Yes, the theory of evolution has to go on the list of What's Important to Know. But is it essential?

What is proof?
Just at that point, the only scientist among us, Dr. Toivo Kallas, professor of biology at the University of Wisconsin and a contributor to the Human Genome Project, cleared his throat.

"If we're making a list of what's important to know in science, I would put the scientific model of proof near the top," he said.

Wow. Kallas really nailed it. Weighing the validity of a scientific claim--that's relevant to me every day. By scientific claim, I mean any claim that can be proved or disproved by using the scientific method. Many claims don't fit that label, of course, such as "I love you," and "That's a beautiful horse."

But lots of everyday claims do fit. For example, a former roommate once chided me for leaving the peanut butter on the counter because, he said, peanut butter causes cancer unless it's refrigerated. How did he know? He heard it from an expert. Did the expert have proof? "Yes, he did," my roommate said confidently. "He explained the whole chain of cause and effect. Once you saw his reasoning, it made perfect sense."

The trouble is, "making perfect sense" is just what doesn't constitute proof in science. The history of science is full of ideas that made perfect sense but turned out to be wrong.

How often do most of us have to weigh a statement like my roommate's about peanut butter? Pretty often, I'd say. Here are three claims I heard just yesterday.

• Virgos tend to be very well organized.
• B vitamins improve your concentration.
• If you sit in a draft, you'll catch a cold.

The discussion about science got me thinking about what is essential knowledge in other disciplines. What is really essential to know about history, for example? What about literature? I decided to tap some real scholars for their opinions.