A locomotive is moving. Someone asks: "What moves it?" A peasant says the devil moves it. Another man says the locomotive moves because its wheels go round. A third asserts that the cause of its movement lies in the smoke which the wind carries away.

The peasant is irrefutable. He has devised a complete explanation. To refute him someone would have to prove to him that there is no devil, or another peasant would have to explain to him that it is not the devil but a German, who moves the locomotive. Only then, as a result of the contradiction, will they see that they are both wrong. But the man who says that the movement of the wheels is the cause refutes himself, for having once begun to analyze he ought to go on and explain further why the wheels go round; and till he has reached the ultimate cause of the movement of the locomotive in the pressure of steam in the boiler, he has no right to stop in his search for the cause. The man who explains the movement of the locomotive by the smoke that is carried back has noticed that the wheels do not supply an explanation and has taken the first sign that occurs to him and in his turn has offered that as an explanation.

The only conception that can explain the movement of the locomotive is that of a force commensurate with the movement observed.

The only conception that can explain the movement of the peoples is that of some force commensurate with the whole movement of the peoples.

Yet to supply this conception various historians take forces of different kinds, all of which are incommensurate with the movement observed. Some see it as a force directly inherent in heroes, as the peasant sees the devil in the locomotive; others as a force resulting from several other forces, like the movement of the wheels; others again as an intellectual influence, like the smoke that is blown away.

So long as histories are written of separate individuals, whether Caesars, Alexanders, Luthers, or Voltaires, and not the histories of all, absolutely all those who take part in an event, it is quite impossible to describe the movement of humanity without the conception of a force compelling men to direct their activity toward a certain end. And the only such conception known to historians is that of power.

This conception is the one handle by means of which the material of history, as at present expounded, can be dealt with, and anyone who breaks that handle off, as Buckle did, without finding some other method of treating historical material, merely deprives himself of the one possible way of dealing with it. The necessity of the conception of power as an explanation of historical events is best demonstrated by the universal historians and historians of culture themselves, for they professedly reject that conception but inevitably have recourse to it at every step.

In dealing with humanity's inquiry, the science of history up to now is like money in circulation- paper money and coin. The biographies and special national histories are like paper money. They can be used and can circulate and fulfill their purpose without harm to anyone and even advantageously, as long as no one asks what is the security behind them. You need only forget to ask how the will of heroes produces events, and such histories as Thiers' will be interesting and instructive and may perhaps even possess a tinge of poetry. But just as doubts of the real value of paper money arise either because, being easy to make, too much of it gets made or because people try to exchange it for gold, so also doubts concerning the real value of such histories arise either because too many of them are written or because in his simplicity of heart someone inquires: by what force did Napoleon do this?- that is, wants to exchange the current paper money for the real gold of actual comprehension.

The writers of universal histories and of the history of culture are like people who, recognizing the defects of paper money, decide to substitute for it money made of metal that has not the specific gravity of gold. It may indeed make jingling coin, but will do no more than that. Paper money may deceive the ignorant, but nobody is deceived by tokens of base metal that have no value but merely jingle. As gold is gold only if it is serviceable not merely for exchange but also for use, so universal historians will be valuable only when they can reply to history's essential question: what is power? The universal historians give contradictory replies to that question, while the historians of culture evade it and answer something quite different. And as counters of imitation gold can be used only among a group of people who agree to accept them as gold, or among those who do not know the nature of gold, so universal historians and historians of culture, not answering humanity's essential question, serve as currency for some purposes of their own, only in universities and among the mass of readers who have a taste for what they call "serious reading."