The endeavour to gain the enemy's line of retreat, and protect our own, on which so much learned erudition has been spent by various writers, he regards as a NATURAL instinct, which will ALWAYS produce itself both in generals and subalterns. "From this arises, in the whole conduct of war, and especially in great and small combats, a PERFECT INSTINCT, which is the security of our own line of retreat and the seizure of the enemy's; this follows from the conception of victory, which, as we have seen, is something beyond mere slaughter. In this effort we see, therefore, the FIRST immediate purpose in the combat, and one which is quite universal. No combat is _imaginable_ in which this effort, either in its double or single form, is not to go hand in hand with the plain and simple stroke of force. Even the smallest troop will not throw itself upon the enemy without thinking of its line of retreat, and in most cases it will have an eye upon that of the enemy."[62] "This is a great _natural law_ of the combat," "and so becomes the pivot upon which ALL strategical and tactical manoeuvres turn." RESERVES--DESTRUCTIVE AND DECISIVE ACT The combat he regards as settled by whoever has the preponderance of moral force at the end; that is, in fresh or only partly used up troops. The combat itself he divides into a destructive and a decisive act. During the long destructive act, or period of fire preparation, the troops engaged gradually wear each other out, and gradually almost cease to count as factors in the decision. "After a fire combat of some hours' duration, in which a body of troops has suffered severe losses--for instance, a quarter or one-third of its numbers--the _débris_ may for the time be looked upon as a heap of cinders. For the men are physically exhausted; they have spent their ammunition; many have left the field with the wounded, though not themselves wounded (compare, for instance, Eylau and the 1870 battles); the rest think they have done their part for the day, and if they get beyond the sphere of danger, do not willingly return to it. The feeling of courage with which they originally started has had the edge taken off, the longing for the fight is satisfied, the original organization is partly destroyed, and the formations broken up." "So that the amount of moral force lost may be estimated by the amount of the Reserves used up, almost as with a foot rule."[63] This goes on till, "In all probability, only the untouched reserve and some troops which, though they have been in action, have suffered very little, are in reality to be regarded as serviceable, and the remainder (perhaps four-sixths) may be looked upon for the present as a "caput mortuum."