It is for the purpose of considering these human motives and personal accidents that I offer these pages; for if we can comprehend Erlon's error, we shall fill the only remaining historical gap in the story of Waterloo, and determine the true causes of that action's result. [Illustration] There are two ways of appreciating historical evidence. The first is the lawyer's way: to establish the pieces of evidence as a series of disconnected units, to docket them, and then to see that they are mechanically pieced together; admitting, the while, only such evidence as would pass the strict and fossil rules of our particular procedure in the courts. This way, as might be inferred from its forensic origin, is particularly adapted to arriving at a foregone conclusion. It is useless or worse in an attempt to establish a doubtful truth. The second way is that by which we continually judge all real evidence upon matters that are of importance to us in our ordinary lives: the way in which we invest money, defend our reputation, and judge of personal risk or personal advantage in every grave case. This fashion consists in admitting every kind of evidence, first hand, second hand, third hand, documentary, verbal, traditional, and judging the general effect of the whole, not according to set legal categories, but according to our general experience of life, and in particular of human psychology. We chiefly depend upon the way in which we know that men conduct themselves under the influence of such and such emotions, of the kind of truth and untruth which we know they will tell; and to this we add a consideration of physical circumstance, of the laws of nature, and hence of the degrees of probability attaching to the events which all this mass of evidence relates. It is only by this second method, which is the method of common-sense, that anything can be made of a doubtful historical point. The legal method would make of history what it makes of justice. Which God forbid! Historical points are doubtful precisely because there is conflict of evidence; and conflict of evidence is only properly resolved by a consideration of the psychology of witnesses, coupled with a consideration of the physical circumstances which limited the matter of their testimony. Judged by these standards, the fatal march and countermarch of Erlon become plain enough. His failure to help either Ney or Napoleon was not treason, simply because the man was not a traitor. It proceeded solely from obedience to orders; but these orders were fatal because Ney made an error of judgment both as to the real state of the double struggle--Quatre Bras, Ligny--and as to the time required for the countermarch. This I shall now show. Briefly, then:-- Erlon, as he was leading his army corps up to help Ney, his immediate superior, turned it off the road before he reached Ney and led it away towards Napoleon. Why did he do this?