Like any other general work in science, it conveys only the knowledge required to stake a claim for the validity of selected theories and hypotheses. The author warrants that anyone else would agree with him after searching for and applying homologous facts. He claims that his individual statements fit into a larger scheme of scientifically testable theory about American history. Given so large a task to be performed in a single volume, clarification and proof of the principles must be by reference to representative and salient cases and instances. History-telling ought generally to be corrective and therapeutic, by which I mean that it should be realistic, moral, and useful.
All pure science has an applied science attached to it, and is indeed dependent ultimately upon it.
So it is perfectly proper and necessary to write history as the application of the pure social sciences to the applied science of bringing about a better world. And we take care to be clear and open, never hypocritical, about what we deem to be a preferable condition of people and society, and about the good and bad consequences of the same event. Thus they reveal themselves to be quite willing in their own case to let ancient morals govern modern conduct. If we did so, we would be making a most important moral judgement and set a low standard for our conduct. I say that we must study the past scientifically and judge it ethically, if we are to derive from history its greatest gifts.