Economics, as we have now seen again and again, is a science of recognizing secondary consequences. It is also a science of seeing general consequences. It is the science of tracing the effects of some proposed or existing policy not only on some special interest in the short run, but on the general interest in the long run. This is the lesson that has been the special concern of this book. We stated it first in skeleton form, and then put flesh and skin on it through more than a score of practical applications. But in the course of specific illustration we have found hints of other general lessons; and we should do well to state these lessons to ourselves more clearly.