Lecture IV

The most peculiar ideas have been expressed to explain this phenomenon. For example, you may have heard people say, “When a young child gets hurt by running into a corner, the reaction is to hit the corner.” An intellectual interpretation of this phenomenon would be that one hits back only if one has consciously received a hurt or an injury consciously inflicted. And this is how the child's response in hitting a table or other object is explained. This kind of definition always tempts one to quote the Greek example of a definition of the human being—that is, a human being is a living creature who has two legs but no feathers. As far as definitions go, this is actually correct. It leads us back into the times of ancient Greece. I won't go into details to show that present definitions in physics are often not much better, because there children are also taught frequently that a human being is a creature that walks on two legs and has no feathers. A boy who was a bit brighter than the rest thought about this definition. He caught a cockerel, plucked its feathers, and took it to school. He presented the plucked bird, saying, “This is a human being! It is a creature that walks on two legs and has no feathers.” Well, definitions may have their uses, but they are almost always one-sided.