Philidor Defense: Nimzowitsch Variation, Klein Variation

The Philidor Defense is a chess opening that starts with the moves 1. e4 e5. The idea behind playing e4 is to control the center of the board and to free up the queen and bishop. The knight on f3 supports this plan by exerting pressure on the e5-pawn. Black responds with d6, which prepares to develop the knight on f6. The Nimzowitsch Variation is introduced on move three with Nf6, attacking the pawn on e4. White, in turn, reinforces the pawn with d4. The Klein Variation, 4. Bc4 aims to develop the bishop with a potential threat to Black's kingside.

Playing e5 in response to e4 is a common and effective way for Black to fight for control of the center of the board. By advancing the pawn to e5, Black creates a pawn duo that can control important squares on the board. Additionally, the pawn on e5 can protect the knight on f6 and potentially free up the queen and bishop. However, by advancing the pawn, Black also creates a target that White can attack with their own pawns or with pieces. It's important for Black to understand this trade-off and be prepared to defend the pawn and maintain control of the center.

The move Nf3 is a standard response to the opening moves of e4 e5. By developing the knight to f3, White exerts pressure on the center of the board and prepares to castle kingside. The knight also provides a threat to capture the pawn on e5 if Black is careless with their defense. Additionally, placing the knight on f3 can support the pawn push to d4, which further strengthens White's position in the center. In sum, Nf3 is a useful and flexible move in the opening, allowing White to control the board and maintain a strong position.

In the Philidor Defense: Nimzowitsch Variation, Klein Variation, Black plays d6 in response to Nf3. This move prepares to develop the knight on f6 and reinforces the pawn on e5. Additionally, d6 can prevent White from playing Ng5 and attacking the pawn on f7. The move also controls the square on e5, denying it to White's knight. While d6 may appear passive, it is a solid and effective move that allows Black to maintain a strong position in the center of the board.

After the moves 1. e4 e5 2. Nf3 d6, White plays d4 to increase their control of the center and open up lines for their pieces. The move also puts pressure on the pawn on e5, which Black is relying on to control the center. This pawn push allows White's bishop on c1 to be developed, while breaking the symmetry in the center of the board. By pushing the pawn, White also frees up the queen and opens lines for possible attacks against Black's king. In sum, d4 is an aggressive and strong move that aims to maintain White's control of the board.

After the moves 1. e4 e5 2. Nf3 d6 3. d4, Black plays Nf6 to put pressure on the e4-pawn and to develop their knight with tempo. The knight also supports the pawn on d6, freeing up the bishop on c8 for development. Additionally, Nf6 puts pressure on the pawn on d4 and can potentially lead to an exchange of pawns which would further open up the center. By playing Nf6, Black continues to contest White's control of the center of the board while developing their pieces. In sum, it is a solid and flexible move that allows Black to maintain a strong position.

In the Philidor Defense: Nimzowitsch Variation, Klein Variation, White plays Bc4 after Nf6. This move aims to develop the bishop with potential threats on Black's kingside while being able to target weak spots in Black's pawn formations. Additionally, Bc4 prepares for castling kingside and helps control the d5-square. The bishop also poses a potential threat to the knight on f6, which is defending the e5-pawn. By playing Bc4, White continues to develop their pieces while applying pressure on Black's position. In sum, it is a flexible and aggressive move that allows White to maintain control of the board.