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By Root 670 0

an indefinitely long inclined plain, and it speeds up as it rolls. Set a ball in motion up an inclined plane, and it slows down as it rolls. Now, set a ball in motion on a perfectly level surface. What does common sense say will happen? It continues to roll without speeding up or slowing down, right? Stands to reason. It can’t do what it does in either of the other two cases when it’s rolling down or up. “Gee, I never thought about it that way,” says common sense. “I better revise my beliefs about motion.” It only took 2 millennia to come up with that thought experiment, but its impact on history can’t be minimized. We now know Galileo’s conclusion as Newton’s first law of motion. Too bad we were not taught it that way.

Galileo’s little thought experiment led to a revision of common sense. The revision required the physicists to scrap Aristotle’s formalization of common sense in favor of a radically different conception of reality, one that tied forces to accelerations instead of velocities and led right to Newton’s second law of motion. The steps are just as easy and obvious, just as commonsensical as the ones we ran through in the last paragraph. After Galileo, it became physicists’ common sense that a ball moving in a straight line at constant velocity doesn’t have any forces acting on it. So, by common sense, if the ball is moving in a straight line but changing velocity, or moving on a curved path (jut another way to change its velocity), there must be a force acting on it. Voilà! Newton’s second law. Common sense.

It would be easy to go on and on until we have built the whole of physics. Starting from physics, the same process results in chemistry and biology.

Science begins as common sense. Each step in the development of science is taken by common sense. The accumulation of those commonsense steps, each of them small, from a commonsense starting place over a 400-year period since Galileo, has produced a body of science that no one any longer recognizes as common sense. But that’s what it is. The real common sense is relativity and quantum mechanics, atomic chemistry and natural selection. That’s why we should believe it in preference to what ordinary experience suggests.

No matter how bizarre the conclusions that science commits us to, they are the latest steps on a long path, one traversed by a methodical, careful process using highly reliable equipment. It’s a path found literally by detecting the mistakes of common sense, one at a time, and avoiding them. It’s too bad there isn’t enough time to teach everyone science as common sense correcting itself.

In what follows, our progress is increasingly going to involve identifying the mistakes that common sense is still making and the dead ends they lead to. That’s because once we get past biology and into the sciences of the mind and human society, we don’t yet have all the theory we need to understand what is going on. At this point, however, we do have a good idea of the kinds of mistakes common sense keeps making. Knowing them is almost enough to answer the yes or no questions we started with in Chapter 1.

Here is some commonsense wisdom: One thing consciousness does is retrieve information from the brain. Someone asks for your birth date or social security number, and up it comes into awareness. Then you read it off your introspection and answer the question. You can’t find your keys, so you concentrate. Suddenly the location pops up into consciousness. Sometimes you have a “senior moment” and forget your boss’s name. Then all of a sudden (when it’s too late) it’s shouting itself out to you inside your head.

Blindsight, the Libet experiments, and the rearview mirror of experience should make us deeply suspicious of this apparently obvious matter. Why shouldn’t your conscious thought about your birth date just be a by-product, a side effect, of whatever is going on nonconsciously in your brain when it makes you answer someone’s question with your date of birth? Why couldn’t the brain’s nonconscious storage of where your keys are produce the conscious thought