opportunity to develop the Queen's Bishop, a game of entirely
different character ensues. The following variations show typical
examples of the way these two variations are liable to develop:

A. (5) P-e3 Kt-c6
(6) P-a3

If White played (6) P-b3 before castling he would get into
trouble because Black could pin his Queen's Knight with Pxd4 and
B-b4. For this reason the maneuver P-a3, Pxc5, P-b4 and B-b2 is
usually adopted to develop the Queen's Bishop. It is true that
this maneuver involves two Pawn moves, which mean a loss of time,
instead of only one, as for instance when playing (6) B-d3, (7)
o-o, (8) P-b3, (9) B-b2. But Black can hardly avoid a similar
loss of time. For if he plays (6) ..., B-d6, he loses two moves
with his Bishop through recapturing on c5 (after (7) Pxc5) and
going back to d6; and if he first exchanges on d4 and then
develops the Bishop to d6, White has an open diagonal for his
Queen's Bishop and need not make any more Pawn moves to develop
him while Black still must move his Queen's Knight's Pawn to get
his Queen's Bishop into play.

(6) ... P-a6
(7) Pxc5 Bxc5
(8) P-b4 B-d6
(9) B-b2 Pxc4
(10) Bxc4 P-b5
(11) B-d3 B-b7

B. (5) Pxd5 Pxd5