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The Philidor Defence is a chess opening characterised by the moves (in algebraic notation):

1.e4 e5

2.Nf3 d6.

Named after the 18th century player François-André Danican Philidor, it has the reputation of being solid if somewhat unambitious.

White usually plays 3.d4 because after most other moves Black can equalise quickly with 3...f5. After 3.d4 Black has several options. One of the most common is 3...exd4, an old move that was abandoned for a while but has been revived. After 4.Nxd4 Nf6 5.Nc3, Black normally plays ...Be7 and ...O-O with a characteristically solid but passive position, but can also fianchetto his bishop on g7 (Bent Larsen tried this in a few games, including a draw against Mikhail Tal in 1969).

The other main option for Black is to maintain the central tension and adopt a setup with ...Nbd7, ...Be7 and ...c6. This plan is called the Hanham Variation and was favored by Nimzowitsch. A common line is 3...Nf6 4.Nc3 Nbd7 5.Bc4 Be7 6.O-O (6.Ng5 is an interesting alternative: after 6...O-O 7.Bxf7+ Rxf7 8.Ne6 Qe8 9.Nxc7 Qd8 10.Nxa8, White is material up, but Black can develop a strong initiative after, for example, 10...b5 11.Nxb5 Qa5+) 6...O-O 7.a4 (to prevent ...b5) 7...c6.

A more aggressive approach for black is 3...f5 (after 3.d4), a move which Philidor himself recommended. This can lead to more open positions than the other lines, but is less often seen.

Black should not play 3...Bg4?, as he will be forced to trade bishop for knight with serious loss of time after 4.dxe5 Bxf3 5.Qxf3 dxe5 6.Bc4, followed by 7. Qb3. The "natural" 6... Nf6 costs a pawn. This was played in the famous "opera box game", when Paul Morphy as White declined to win the pawn but retained a strong initiative after 7...Qe7 8.Nc3.

An alternative approach for White is to play 3.Bc4, and either delay d4 or forego it altogether and instead play d3.

As of 2004, there are no top players who employ the Philidor Defence with any regularity, although Etienne Bacrot and Liviu-Dieter Nisipeanu have occasionally experimented with it.

The ECO code for Philidor Defence is C41.