Chess Opening Theory/1. e4/1...e5/2. Nf3/2...d6/3. d4/3...Bg4

Philidor defence 3...Bg4?! 3...Bg4?! may look like an attempt to defend the e4 pawn, but it doesn't succeed. Though it appears that White's knight is pinned to their queen, after 4. dxe5 dxe5 5. Qxd8+ (trades queens and unpins the knight) Kxd8, White's knight is unpinned and can take back on e5 anyway. If 4... Bxf3 first, as in the Opera Game, 5. Qxf3 dxe4 6. Bc4 and White is threatening a crushing attack on f7. Instead, after 3... Bg4 4. dxe5 Black can gambit the pawn with 4...Nd7, the Albin-Blackburne gambit. It continues 5. exd6 Bxd6, and Black has three pieces developed to White's one. They usually continue with Qe2 and long castles. Theory table References