e Emperor thought, to but one of two results: either the great majority
of the Prussian force, coming up to retrieve this first disaster, would be
defeated in detail as it came; or, more probably, finding itself cut off
from all aid on the part of Wellington's forces to the west and its head
crushed, the long Prussian line would roll up backwards upon its
communications towards the east, whence it had come.

In either case the prime object of Napoleon's sudden move would have been
achieved; and, with the body upon the left, under Ney, pushing up the
Brussels road, the body upon the right, under Grouchy, pushing back the
head of the Prussian line eastward, the two halves of the Allies would be
separated altogether, and could later be dealt with, each in turn. The
capital disadvantage under which Napoleon suffered--the fact that he had
little more than half as many men as his combined enemies--would be
neutralised, because he would, after the separation of those enemies into
two bodies, be free to deal with either at his choice. Their
communications came from diametrically opposite directions,[5] and, as the
plan of each depended upon the co-operation of the other, their separation
would leave them confused and without a scheme.

Napoleon in all this exaggerated the facility of the task before him; but
before we go into that, it is essential that the reader should grasp a
certain character in all military affairs, to misunderstand which is to
misread the history of armies.

_This characteristic is the necessary uncertainty under which every
commander lies as to the disposition, the number, the order, and the
information of his opponents._

It is a _necessary_ characteristic in all warfare, because it is a prime
duty in the conduct of war to conceal from your enemy your numbers, your
dispositions, and the extent of your information. It is a duty which every
commander will always fulfil to his best ability.

It is therefore a characteristic, be it noted, which no development of
human science can conceivably destroy, for with every advance in our means
of communicating information we advance also in our knowledge of the means
whereby the new means of communication may be interrupted. An advantage
over the enemy in the means one has of acquiring knowledge with regard to
him must, of course, always be of supreme importance, and when those means
are novel, one side or the other is often beforehand for some years with
the ne