Philidor Defence

The Philidor Defence (or Philidor's Defence) a chess opening characterised by the moves:
The opening is named after the famous 18th-century player François-André Danican Philidor, who advocated it as an alternative to the common 2...Nc6. His original idea was to challenge White's by the pawn thrust ...f7–f5.
Today, the Philidor is known as a but passive choice for Black, and is seldom seen in top-level play except as an alternative to the heavily analysed openings that can ensue after the normal 2...Nc6. It is considered a good opening for amateur players who seek a defensive strategy that is simpler and easier to understand than the complex positions that result from an opening such as the French Defence.
The "Encyclopaedia of Chess Openings" code for Philidor Defence is C41.
Use.
The Philidor occurred in one of the most famous games ever played, "The Opera Game" played in 1858 between the American chess master Paul Morphy and two strong amateurs, the German noble Duke Karl of Brunswick and the French aristocrat Count Isouard. The game continued 3.d4 Bg4, a deviation from modern standard lines. The Philidor Defence declined in popularity as became more developed, and it had almost completely vanished from top-tier chess by World War I.
, there are no top players who employ the Philidor with regularity, although Étienne Bacrot and Liviu-Dieter Nisipeanu have occasionally experimented with it in classical play. However, its popularity in master play has increased slightly over the last 20 years. It has also become fairly popular in rapid, blitz, and bullet chess.
Main line: 3.d4.
With 3.d4 White immediately challenges Black in the . Black has several options.
3...exd4.
The most common Black response is 3...exd4 which relieves the central , although it gives up the centre. After 4. Nxd4 Nf6 5. Nc3, Black normally continues ...Be7 and ...0-0 (the Antoshin Variation) and achieves a strong defensive position. A sample line is: 4.Nxd4 Nf6 5.Nc3 Be7 6.Bc4 0-0 7.0-0 c5, and the position is . 
In this line Black can also fianchetto his bishop to g7, although this is uncommon. Bent Larsen tried this in a few games, including a draw against Mikhail Tal in 1969.
Instead of 4.Nxd4, White can play 4. Qxd4, as Paul Morphy favoured, intending 4...Nc6 5.Bb5 Bd7 6.Bxc6 Bxc6 7.Nc3 Nf6 8.Bg5 followed by 0-0-0. This line was played in many 19th-century games.
Hanham Variation.
The other main option for Black is to maintain the central tension and adopt a setup with ...Nd7, ...Be7, and ...c6. This plan is named the Hanham Variation (after the American chess master James Moore Hanham) and was favoured by Aron Nimzowitsch. A common line is: 3... Nf6 4. Nc3 Nbd7 5. Bc4 Be7 6. 0-0 (6.Ng5 is an interesting alternative: after 6...0-0 7.Bxf7+ Rxf7 8.Ne6 Qe8 9.Nxc7 Qd8 10.Nxa8, White is up , but Black can develop a strong initiative after, for example, 10...b5 11.Nxb5 Qa5+) 6... 0-0 7. a4 (to prevent ...b5) c6 (see diagram).
Grandmaster (GM) Larry Kaufman notes that the Hanham Variation aims to maintain Black's pawn on e5, analogously to closed lines of the Ruy Lopez, and opines that "it would be quite popular and on a par with the major defences to 1.e4, except for the annoying detail that Black can't actually reach the Hanham position by force."
As an alternative to 4.Nc3 in response to Black's 3...Nf6, according to both Kaufman and GM Christian Bauer, White retains some advantage with: 4. dxe5 Nxe4 5. Qd5! (the Rellstab Variation; 5.Nbd2 is the Sokolsky Variation) 5... Nc5 6. Bg5 Be7 Qxd6 8. Nc3.
Alternative move order.
Black sometimes tries 3... Nd7 intending 4.Nc3 Ngf6, reaching the Hanham Variation. But then 4. Bc4! is awkward for Black to meet, since 4...Ngf6 loses to 5.Ng5, and 4...Be7 loses a pawn to 5.dxe5 Nxe5 (5...dxe5 6.Qd5! wins) 6.Nxe5 dxe5 7.Qh5! So 4... c6 is best for Black, but leaves White with the advantage of the after 5. 0-0 Be7 6. dxe5 dxe5 (6...Nxe5 loses a pawn to 7.Nxe5 dxe5 8.Qh5) 7. Ng5! Bxg5 8. Qh5! Qe7 and now 9.Bxg5 or 9.Qxg5.
Black experiments to reach the Hanham Variation.
In recent years, Black has experimented with other move orders in an attempt to reach the Hanham Variation while avoiding 3...Nf6 4.dxe5! and 3...Nd7 4.Bc4! 
Philidor Countergambit: 3...f5.
A more aggressive approach for Black after 3.d4 is 3...f5 (diagram), Philidor's original intention and recommendation. In the 19th century, 3...f5 was also played by Paul Morphy. The move can lead to more than the other lines, but is often considered dubious. Others maintain that 3...f5 is a valid idea. GM Tony Kosten considers the move respectable in his monograph on the opening. The move was also played by David Bronstein and by Teimour Radjabov.
After 3...f5 White has several ways to proceed:
3...Bg4?!
Inferior is 3...Bg4, in light of 4. dxe5 Bxf3 (Black cannot recapture since 4...dxe5 5.Qxd8+ Kxd8 6.Nxe5 wins a clean pawn; or, Black can gambit a pawn with 4...Nd7, the Albin Variation) 5. Qxf3 (or White can obtain an endgame advantage with 5.gxf3 dxe5 6.Qxd8+ Kxd8 7.f4 Maróczy) 5... dxe5 6. Bc4 giving White the advantage of the in an open position as well as a large advantage. Black cannot block the attack on the f7-pawn with the "natural" 6...Nf6? because White wins a pawn with 7.Qb3 (played in the famous "Opera Game", where Morphy as White refrained from taking the b7-pawn and retained a strong after 7...Qe7 8.Nc3). Black does better with 6...Qf6 7.Qb3 Bc5 8.0-0 Bb6 9.a4 a5 10.Nc3 Ne7 11.Be3 Nd7 12.Rad1+/−, or 6...Qd7!? (Maróczy).
References.
Bibliography