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“Légal’s Mate” is a famous chess mating pattern that involves delivering checkmate in just a few moves, often in the opening phase of the game. It’s named after Sire de Légal, a French player who popularized this mating pattern in the 18th century.

The typical sequence leading to Légal’s Mate occurs in the Philidor Defense or Philidor’s Defense, which begins with the moves:

1. e4 e5
2. Nf3 d6
3. d4 Bg4?

Black’s third move, Bg4, is a mistake, allowing White to exploit the position immediately with:

4. dxe5 Bxf3?
5. Qxf3 dxe5
6. Bc4

At this point, White threatens checkmate on f7 while also eyeing the weakened f7-square. Black has few options to defend against the imminent threat, such as playing Qe7 or Nf6, but neither provides adequate defense.

If Black attempts to defend with 6…Qe7, hoping to block the diagonal, White can respond with 7. Qb3, attacking the b7-pawn and preparing for a subsequent Bxf7+.

If Black tries 6…Nf6, White can proceed with 7. Qb3, once again threatening Bxf7+ and a subsequent checkmate.

The key to Légal’s Mate is the exploitation of the f7-square weakness due to the early bishop sortie by Black. It demonstrates the importance of controlling central squares and developing pieces harmoniously while capitalizing on opponent’s weaknesses.

Légal’s Mate is instructive as it teaches players to avoid premature piece movements, especially moving the f8 bishop in the opening, which can leave Black’s position vulnerable to quick attacks and tactics centered around the f7-square.