In other words, Erlon's zigzag kept the 20,000 of the First Corps out of action all day. Had they been with Ney, the Allies under Wellington at Quatre Bras would have suffered a disaster. Had they been with Napoleon, the Prussians at Ligny would have been destroyed. As it was, the First Army Corps managed to appear on _neither_ field. Wellington more than held his own; the Prussians at Ligny escaped, to fight two days later at Waterloo.
Such are the facts, and they explain all that followed (see Map, next page).
But it has rightly proved of considerable interest to historians to attempt to discover the human motives and the personal accidents of temperament and misunderstanding which led to so extraordinary a blunder as the utter waste of a whole army corps during a whole day, within an area not five miles by four.
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.
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.