The point where the idea of a strategic reserve begins to become inconsistent is not difficult to determine: it lies in the supreme decision. Employment must be given to all the forces within the space of the supreme decision, and every reserve (active force available) which is only intended for use after that decision is opposed to common sense.
If, therefore, tactics has in its reserves the means of not only meeting unforeseen dispositions on the part of the enemy, but also of repairing that which never can be foreseen, the result of the combat, should that be unfortunate; Strategy on the other hand must, at least as far as relates to the capital result, renounce the use of these means. As A rule, it can only repair the losses sustained at one point by advantages gained at another, in a few cases by moving troops from one point to another; the idea of preparing for such reverses by placing forces in reserve beforehand, can never be entertained in Strategy.
We have pointed out as an absurdity the idea of a strategic reserve which is not to co-operate in the capital result, and as it is so beyond a doubt, we should not have been led into such an analysis as we have made in these two chapters, were it not that, in the disguise of other ideas, it looks like something better, and frequently makes its appearance. One person sees in it the acme of strategic sagacity and foresight; another rejects it, and with it the idea of any reserve, consequently even of a tactical one. This confusion of ideas is transferred to real life, and if we would see a memorable instance of it we have only to call to mind that Prussia in 1806 left a reserve of 20,000 men cantoned in the Mark, under Prince Eugene of Wurtemberg, which could not possibly reach the Saale in time to be of any use, and that another force Of 25,000 men belonging to this power remained in East and South Prussia, destined only to be put on a war-footing afterwards as a reserve.
After these examples we cannot be accused of having been fighting with windmills.
The road of reason, as we have said, seldom allows itself to be reduced to a mathematical line by principles and opinions. There remains always a certain margin. But it is the same in all the practical arts of life. For the lines of beauty there are no abscissae and ordinates; circles and ellipses are not described by means of their algebraical formulae. The actor in War therefore soon finds he must trust himself to the delicate tact of judgment which, founded on natural quickness of perception, and educated by reflection, almost unconsciously seizes upon the right; he soon finds that at one time he must simplify the law (by reducing it) to some prominent characteristic points which form his rules; that at another the adopted method must become the staff on which he leans.