y calculate.

Having determined the normal, we are at once in a stronger position. Any
proposal can be compared with it, and we can proceed to discuss clearly the
weight of the factors which prompt us to depart from the normal. Every case
must be judged on its merits, but without a normal to work from we cannot
form any real judgment at all; we can only guess. Every case will assuredly
depart from the normal to a greater or less extent, and it is equally
certain that the greatest successes in war have been the boldest departures
from the normal. But for the most part they have been departures made with
open eyes by geniuses who could perceive in the accidents of the case a
just reason for the departure.

Take an analogous example, and the province of strategical theory becomes
clear at once. Navigation and the parts of seamanship that belong to it
have to deal with phenomena as varied and unreliable as those of the
conduct of war. Together they form an art which depends quite as much as
generalship on the judgment of individuals. The law of storms and tides, of
winds and currents, and the whole of meteorology are subject to infinite
and incalculable deflections, and yet who will deny nowadays that by the
theoretical study of such things the seaman's art has gained in coherence
and strength? Such study will not by itself make a seaman or a navigator,
but without it no seaman or navigator can nowadays pretend to the name.
Because storms do not always behave in the same way, because currents are
erratic, will the most practical seaman deny that the study of the normal
conditions are useless to him in his practical decisions?

If, then, the theoretical study of strategy be approached in this way--if,
that is, it be regarded not as a substitute for judgment and experience,
but as a means of fertilising both, it can do no man harm. Individual
thought and common-sense will remain the masters and remain the guides to
point the general direction when the mass of facts begins to grow
bewildering. Theory will warn us the moment we begin to leave the beaten
track, and enable us to decide with open eyes whether the divergence is
necessary or justifiable. Above all, when men assemble in Council it will
hold discussion to the essential lines, and help to keep side issues in
their place.

But beyond all this there lies in the theory of war yet another element of
peculiar value to a maritime Empire. We are accustomed, partly for
conv