the command of the centre, but that the opening up of files and
diagonals for one's pieces towards the centre is an important
moment in the fight for positional advantage.

Considerations of this kind will help to improve our judgment in
many of the various openings treated in the following pages.

We will class the openings in this way:

A. White 1. P-K4.

(a) Black 1. P-K4
(b) Black 1. Any other move

B. White 1. P-Q4.

(a) Black 1. P-Q4
(b) Black 1. Any other move

C. White 1. Any other move

We shall find that openings classed under C generally lead to
positions treated under A and B.

A. We have already come to the conclusion that after 1. P-K4, P-
K4 White does well to try to force the exchange of Black's centre
pawn on Q4 or KB4, and that Black will try to counteract this,
unless by allowing the exchange he gets a chance of exerting
pressure in the centre by means of his pieces.