into our subject.

In the first chapter, when considering special cases in
elementary combinations, we have already noticed the important
part played in each skirmish by the balance between the attacking
and defending units. Speaking quite generally, common-sense will
tell us that, in all operations on the chess-board, the main
consideration for the defence will be to maintain that balance,
and that there is only justification for an attack when it is
possible to concentrate more forces on the strategic point than
can be mustered by the defence. However, one very important point
must not be neglected, though I did not touch upon it when
discussing elementary combinations for fear of complicating
matters for beginners: the balance between the contending forces
is by no means established by their numerical equality. A
paramount factor is the mobility of such forces, and as soon as
it is no longer one of the elementary cases of capture and
recapture described previously, this factor must be taken into
account in order to decide, on a general survey, whether there is
a sufficient defence to an impending attack, or whether one's own
intended attack is likely to prevail. That mobility is the first
and foremost consideration should be self-evident, since the
relative value of the pieces can only make itself felt by their
greater or lesser mobility.

Except in certain positions, which are brought about by some
particular array of the pieces, the intrinsic value of a Rook is
greater than that of a Bishop, because it can command all the
squares on the board, whilst a Bishop is tied to its own colour;
Knight and Bishop are considered equivalent, because the Knight's