The importance of precautions against surprise, of
preserving the mobility of the columns, and of providing for
concentration on short notice whenever it may be necessary, is not lost
sight of, but is dwelt upon with great frequency. But military rules are
not more inflexible than other human rules. Though they are based upon
fixed principles, cases may, and do, arise when they cannot be strictly
adhered to,--sometimes when they ought not to be. When should they be
strictly observed? When and how far is it prudent to depart from them?
"These questions," says General Dufour, "admit of no answers.
Circumstances, which are always different, must decide in each
particular case that arises. Here is the place for a general to show his
ability. The military art would not be so difficult in practice, and
those who have become so distinguished in it would not have acquired
their renown, had it been a thing of invariable rules. To be really a
great general, a man must have great tact and discernment in order to
adopt the best plan in each case as it presents itself; he must have a
ready _coup d'oeil_, so as to do the right thing at the right time and
place; for what is excellent one day may be very injurious the next. The
plans of a great captain seem like inspirations, so rapid are the
operations of the mind from which they proceed: notwithstanding this,
everything is taken into account and weighed; each circumstance is
appreciated and properly estimated; objects which escape entirely the
observation of ordinary minds may to him seem so important as to become
the principal means of inducing him to pursue a particular course. As a
necessary consequence, a deliberative council is a poor director of the
operations of a campaign. As another consequence, no mere theorizer can
be a great general."

Battles, on which the fortune of the campaign must turn at last, receive
a large share of attention. The decision of the question as to when they
shall be fought, though sometimes admitting of no choice, is more often,
with a skilful general, a matter of pure calculation, depending upon
fixed principles, which General Dufour recites in a few brief, but
suggestive sentences. His directions for the disposition and manoeuvres
of the forces in both offensive and defensive battles are quite
complete, though the thousand varying circumstances by which these may
be modified, and which render it impossible for one battle to be a copy
of another, c