I. (4) ...  Ktb8-d7
          (5) B-g5

The fact that White can develop his Queen’s Bishop without difficulty while Black cannot do so has made the Queen’s Gambit one of the most popular openings.

(5) ...  B-e7 (6) P-e3 o-o (7) B-d3 P-b6 (8) o-o B-b7 (9) Pxd5 Pxd5 (10) R-c1

White is two moves ahead in the development, as Black has still to move his c-Pawn before he can get his Queen’s Rook into play.  In the meantime White can mobilize his King’s Rook with Q-e2 and Rf1-d1, with a view to opening the Queen’s file by Pd4xc5.

      II. (4) ...  P-c5

If White now Plays P-e3, holding his Pawn-center, a symmetrical development follows on both sides.  If, however, White takes his 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

The idea of this exchange is to create a weak Pawn on d5 against which later on an attack can be instituted.  However, it is very doubtful whether the Pawn on d5 is really weak.  Experience has shown that Black wins just as many games as White in this opening; the reason is probably that White, in order to open the Queen’s file for attack on d5, has to give away his center-Pawn so that Black has more freedom for his pieces in the center.

(6) P-g3 Kt-c6
(7) B-g2 B-e6
(8) B-g5 B-e7
(9) o-o o-o
(10) Pxc5 Bxc5
(11) R-c1 B-e7
(12) Kt-d4 or Q-a4 followed by
R-f1-d1.

Instead of developing the King’s Bishop to g2 White can just as well play (6) B-g5 or f4, (7) P-e3 and (8) B-d3.  In either case the success depends rather on clever maneuvering in the middle-game than on an advantage inherent to the opening.