Modern Defense: Semi-Averbakh Variation, Polish Variation

The move 1. Nf3 is a flexible move for white, as it prepares either d4 or g3. It also aims to control the center squares and develop the knight to an active square. This move can transpose into several different opening systems, such as the King's Indian Defense or the Nimzo-Indian Defense. In this particular line, after 1. Nf3 c5 2. c4 g6 3. d4 Bg7 4. e4 Qb6, white has to be careful not to lose a pawn on c4, as the black queen is putting pressure on that square. Instead, white can choose to defend the pawn with 5. Nc3 or 5. d5, both of which lead to complex and dynamic positions.

The move c5 is a common response for Black after 1. Nf3, as it aims to control the center and challenge white's control of d4. By playing c5, Black prepares to develop the queen's bishop to g7 and potentially fianchetto it to control the long diagonal. Additionally, the move c5 creates counterplay on the queenside and can allow Black to gain space and pressure white's position. However, Black must be careful to avoid losing a pawn on c5, as it may become weak if left unprotected.

The move c4 by White is a natural response to Black's move c5 since it aims to control more space in the center and create a protected pawn chain. By playing c4, White prepares to develop the queen's knight to c3 and support the d4 pawn. This move also puts pressure on Black's pawn on d5 and restricts the mobility of Black's knight on c6. However, White must be careful not to become overextended in the center, as Black may attempt to undermine the pawn chain with moves like b5 or d5.

In the Modern Defense: Semi-Averbakh Variation, Polish Variation, Black wants to play g6 after the moves 1. Nf3 c5 2. c4. This move prepares to fianchetto the king's bishop to g7, which is a common motif in many variations of the Modern Defense. By controlling the long diagonal, Black can put pressure on White's center and potentially target the weak b2 and d4 pawns. Additionally, the move g6 creates a strong pawn chain on c5, d6, and e5, which can provide a solid foundation for Black's position. However, Black must be careful not to weaken the f6 square and allow White to launch an attack with moves like Ng5 or e4.

After the moves 1. Nf3 c5 2. c4 g6, White wants to play d4. This move aims to control the center, develop the queen's bishop to a potentially active square on d3, and challenge Black's control of the d4 square. By advancing the d-pawn, White also opens up lines for the queen and the light-squared bishop. If Black takes the pawn, White can recapture with the pawn or knight and maintain control of the center. However, White must be careful not to become overextended, as Black can create counterplay on the kingside and potentially target the weak b2 pawn.

After the moves 1. Nf3 c5 2. c4 g6 3. d4, Black wants to play Bg7. This move aims to develop the bishop to an active square and control the long diagonal, which is often used for attacking purposes. By developing the bishop to g7, Black also prepares to castle kingside and potentially support the advance of the f-pawn to create further pressure on White's position. Additionally, the bishop on g7 can participate in attacks on the queenside or support the central pawns in the event of a pawn break like e5 or d5. However, Black must be careful not to leave the f6 square too weak, as White might try to exploit this weakness with a knight or queen sacrifice.

In the Modern Defense: Semi-Averbakh Variation, Polish Variation, White wants to play e4 after the moves 1. Nf3 c5 2. c4 g6 3. d4 Bg7. This move aims to gain more space in the center and potentially break open lines for the queen and bishop. By playing e4, White forces Black to make a decision about the control of the d4 square and can potentially create weaknesses in Black's position. Additionally, the move e4 can provide a protected square for the knight on c3 and prepare for a piece sacrifice on f7. However, White must be careful not to overextend too early in the game, as Black can create counterplay by attacking the weakened central squares.

After the moves 1. Nf3 c5 2. c4 g6 3. d4 Bg7 4. e4, Black wants to play Qb6. This move aims to put pressure on the c4 pawn and potentially gain control of the b-file. By attacking the pawn on c4, Black can force White to make a decision about the protection of this pawn and potentially create weaknesses in White's position. Additionally, the move Qb6 can prepare for a future move like b5 or a5 to create counterplay on the queenside. However, Black must be careful not to overcommit to the queenside, as White can attack Black's weakened pawns with moves like Bb5 or Na3.