Editing Philidor Defence (section)

==Main line: 3.d4 <span class="anchor" id="Main line"></span>==
With 3.d4, White immediately challenges Black in the {{chessgloss|centre}}. Black has several options.

===3...exd4===
The most common Black response is 3...exd4 which relieves the central {{chessgloss|tension}}, although it gives up the centre. After 4.Nxd4 Nf6 (4...d5 5.exd5, the [[Louis Paulsen|Paulsen]] Attack,<ref>Hooper & Whyld 1996, p. 293. ''Paulsen Attack''.</ref> continues 5...Qxd5 6.Qe2+ Be7 7.Nb5 Na6 8.N1c3{{chesspunc|+/{{=}}}} Paulsen<ref>Matanović 1997 (Vol C), p. 214, n. 19.</ref>) 5.Nc3, Black normally continues ...Be7 and ...0-0 (the [[Vladimir Antoshin#Philidor Defence|Antoshin Variation]]) and achieves a strong defensive position. A sample line is: 5...Be7 6.Bc4 0-0 7.0-0 c6, and the position is almost {{chessgloss|equality|equal}}. 

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 (chess)|draw]] against [[Mikhail Tal]] in 1969.<ref>{{cite web |url=https://www.chessgames.com/perl/chessgame?gid=1139887 |title=Mikhail Tal vs. Bent Larsen, Eersel NED (1969) |website=[[Chessgames.com]] }}</ref>

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===
{{Chess diagram 
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|rd|  |bd|qd|  |rd|kd|  
|pd|pd|  |nd|bd|pd|pd|pd
|  |  |pd|pd|  |nd|  |  
|  |  |  |  |pd|  |  |  
|pl|  |bl|pl|pl|  |  |  
|  |  |nl|  |  |nl|  |  
|  |pl|pl|  |  |pl|pl|pl
|rl|  |bl|ql|  |rl|kl|  
|Position after 7...c6. Black's aim in the Hanham is a {{chessgloss|strongpoint}} defence of e5.
}}

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 [[United States of America|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 {{chessgloss|material}}, but Black can develop a strong [[Initiative (chess)|initiative]] after, for example, 10...b5 11.Nxb5 Qa5+) 6...0-0 7.a4 (to prevent ...b5) c6 ({{em|see diagram}}).

[[Grandmaster (chess)|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."<ref>Kaufman 2004, p. 65.</ref>

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{{chesspunc|!}} Nxe4 5.Qd5! (the [[Ludwig Rellstab (chess player)|Rellstab]] Variation;<ref>Hooper & Whyld 1996, p. 334. ''Rellstab Variation''.</ref> 5.Nbd2 is the [[Alexey Sokolsky|Sokolsky]] Variation<ref>Hooper & Whyld 1996, p. 378. ''Sokolsky Variation''.</ref>) 5...Nc5 6.Bg5 Be7 7.exd6 Qxd6 8.Nc3.<ref name="Kaufman p.69">Kaufman 2004, p. 69.</ref><ref>Bauer 2006, p. 32.</ref>

====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.dxe5 Nxe5 (5...dxe5{{chesspunc|??}} 6.Ng5! wins) 6.Nxe5 dxe5 7.Bxf7+ Kxf7 8.Qxd8 Bb4+ 9.Qd2 Bxd2+ 10.Nxd2 winning a pawn, and 4...Be7 loses a pawn to 5.dxe5 Nxe5 (5...dxe5?? 6.Qd5! wins) 6.Nxe5 dxe5 7.Qh5!<ref name="Kaufman p.69"/><ref>Bauer 2006, p. 16.</ref> So 4...c6 is best for Black, but leaves White with the advantage of the {{chessgloss|bishop pair}} 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.<ref>Bauer 2006, pp. 17–22.</ref>

====Black experiments to reach the Hanham Variation====
In recent years, Black has experimented with other {{chessgloss|move orders}} in an attempt to reach the Hanham Variation while avoiding 3...Nf6 4.dxe5! and 3...Nd7 4.Bc4! 
*One such line is 1.e4 d6 2.d4 Nf6 3.Nc3 Nbd7 intending 4.Nf3 e5. White can deviate, however, with 4.f4{{chesspunc|!?}}<ref>Bauer 2006, p. 179.</ref><ref name="Kaufman 2004, p. 199">Kaufman 2004, p. 199.</ref> or even 4.g4!?<ref>Bauer 2006, pp. 197–206.</ref> 
*Another try is 1.e4 d6 2.d4 Nf6 3.Nc3 e5 which [[Transposition (chess)|transposes]] to the Hanham after 4.Nf3 Nbd7, but White can instead try to gain a small advantage with 4.dxe5 (Kaufman opines that 4.Nge2 is "also promising") 4...dxe5 5.Qxd8+ Kxd8 6.Bc4.<ref name="Kaufman 2004, p. 199"/> After 4.dxe5, Bauer concludes that "White stands a trifle better", but that "provided he plays accurately, Black doesn't have much to fear following 6.Bc4, by choosing any of the three valid replies, 6...Ke8, 6...Bb4, or 6...Be6. Then 7.Bxe6 fxe6 his position remains a hard nut to crack."<ref>Bauer 2006, p. 174.</ref>

===Philidor Countergambit: 3...f5 <span class="anchor" id="Philidor Countergambit"></span>===
{{Chess diagram 
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|rd|nd|bd|qd|kd|bd|nd|rd
|pd|pd|pd|  |  |  |pd|pd
|  |  |  |pd|  |  |  |  
|  |  |  |  |pd|pd|  |  
|  |  |  |pl|pl|  |  |  
|  |  |  |  |  |nl|  |  
|pl|pl|pl|  |  |pl|pl|pl
|rl|nl|bl|ql|kl|bl|  |rl
| Philidor Countergambit: 3...f5!?
}}

A more aggressive approach for Black after 3.d4 is 3...f5{{chesspunc|!?}} ({{em|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 {{chessgloss|open game|open positions}} than the other lines, but is often considered dubious.<ref>Kaufman 2004, p. 22.</ref><ref>Bauer 2006, pp. 22–32.</ref> Others maintain that 3...f5 is a valid idea. GM [[Tony Kosten]] considers the move respectable in his monograph on the opening.<ref>Tony Kosten, ''Winning with the Philidor'', Batsford Chess, 1992.</ref> The move was also played by [[David Bronstein]] and by [[Teimour Radjabov]].

After 3...f5 White has several ways to proceed:
*4.Nc3 (the [[Johannes Zukertort|Zukertort]] Variation<ref>Hooper & Whyld 1996, p. 460. ''Zukertort Variation''.</ref>) and White obtains a clear advantage:
**4...fxe4 5.Nxe4 d5 (if 5...Nf6 6.Nxf6 gxf6 7.dxe5 fxe5 8.Bc4 Qf6 9.Ng5{{chesspunc|+/−}} [[Lev Polugaevsky|Polugaevsky]]<ref>Matanović 1981 (Vol C), p. 196, n. 21.</ref>) 6.Nxe5 dxe4 7.Qh5+ g6 8.Nxg6 Nf6 (if 8...hxg6 9.Qxh8 Be6 10.Qe5+/− Larsen) 9.Qe5+ Kf7 (if 9...Be7 10.Nxh8 Nc6 11.Bb5 Qd5 12.Bg5+/− Zukertort<ref>Matanović 1981 (Vol C), p. 197, n. 24.</ref>) 10.Bc4+ Kg7 11.Bh6+ Kxh6 12.Nxh8 Bb4+ 13.c3 Qxh8 14.cxb4+/− (Keres).<ref>Matanović 1997 (Vol C), p. 214, n. 6.</ref> 
**4...exd4 5.Qxd4 fxe4 (if 5...Nf6 6.e5!<ref name=Korn_note(p) />) 6.Bg5 Nf6 7.Nxe4 Be7 8.Bc4 Nc6 9.Qe3+/− ([[Veniamin Sozin|Sozin]]).<ref>Matanović 1997 (Vol C), p. 214, n. 3.</ref>
**4...Nf6 5.dxe5 Nxe4 6.Nxe4 fxe4 7.Ng5 d5 8.e6 Bc5 9.Nxe4!+/− (Sozin, Sokolsky).<ref name=Korn_note(p) />
*4.Bc4 leads to clear advantage for White:
**4...exd4 5.Ng5 Nh6 6.0-0 (6.Nxh7, the [[Carl Jaenisch|Jaenisch]] Variation,<ref>Hooper & Whyld 1996, p. 185. ''Jaenisch Variation''.</ref> leads to an {{chesspunc|unclear}} position after 6...Ng4! 7.Nxf8 Kxf8 8.Qxd4 Nc6<ref name="2C_note14">Matanović 1981 (Vol C), p. 196, n. 14.</ref>) 6...Nc6 7.Re1 f4 (or 7...fxe4 8.Nxe4 Ne5 9.Bxh6 gxh6 10.f4 Nxc4 11.Nxd6+ +/−) 8.Bxf4 Qf6 9.Qd2 Ne5 10.Be2 Bg4 11.f3 Bd7 12.Bg3 0-0-0 13.f4+/−.<ref name=3C_note2 />  
**4...Nf6 5.Ng5 Qe7 (or 5...d5 6.dxe5 dxc4 7.Qxd8+ Kxd8 8.exf6+/−) 6.Bf7+ Kd8 7.Bb3 exd4 8.0-0+/− ([[Johann Berger|Berger]]).<ref name=2C_note14 />
**4...fxe4 5.Nxe5 d5 6.Qh5+ g6 7.Nxg6 Nf6 8.Qe5+ Be7 and continuing either 9.Qxe7+,<ref name=Korn_note(p) /> 9.Nxh8 ([[Wilhelm Steinitz|Steinitz]]),<ref name="3C_note2">Matanović 1997 (Vol C), p. 214, n. 2.</ref> or 9.Bb5+ ([[Paul Keres|Keres]]).<ref name=3C_note2 />
*4.dxe5 forces Black to complicate matters further with 4...fxe4 5.Ng5 d5 with an unclear position.<ref name=3C_note2 /> 
**After 6.e6 (the [[Ercole del Rio|del Rio]] Attack<ref>Hooper & Whyld 1996, p. 104. ''del Rio Attack''.</ref>), White obtains the upper hand after 6...Bc5 7.Nc3 (the [[Johann Berger|Berger]] Variation<ref>Hooper & Whyld 1996, p. 36. ''Berger Variation''.</ref>), or 6...Nh6 7.Nc3! (Berger);<ref name="2C_note10">Matanović 1981 (Vol C), p. 196, n. 10.</ref> however, Black can maintain lack of clarity with 6...Nf6!? 7.Nf7 Qe7 8.Nxh8 Bxe6, or 6...Bb4+ 7.c3 Bc5 8.Nf7 Qf6 9.Be3 Bxe6 10.Nxh8 Bxe3 11.fxe3 Qh4+ 12.g3 Qh6 13.Qd2 Nd7 14.c4 Ne5 15.Be2 dxc4 16.Nc3 Nd3+ 17.Bxd3 exd3 (Makarov).<ref name=2C_note10 /><ref>Matanović 1981 (Vol C), p. 196, n. 13.</ref>
**White also has 6.Nc3!? (Steinitz) and 6.c4.<ref>Matanović 1981 (Vol C), p. 196, n. 9.</ref>        
*4.exf5 e4 5.Ng5 Bxf5 6.Nc3 and White has a slight plus after 6...Nf6 7.f3 (Sozin),<ref>Matanović 1981 (Vol C), p. 196, n. 8.</ref> or 6...d5 7.f3.<ref name="Korn_note(p)">Korn 1982, p. 16, n. (p).</ref>

===3...Bg4?!===
Inferior is 3...Bg4{{chesspunc|?!}}, in light of 4.dxe5 Bxf3 (Black cannot recapture since 4...dxe5{{chesspunc|?}} 5.Qxd8+ Kxd8 6.Nxe5 wins a clean pawn; or, Black can gambit a pawn with 4...Nd7, the [[Adolf Albin|Albin]] Variation<ref>Hooper & Whyld 1996, p. 6. ''Albin Variation''.</ref>) 5.Qxf3 (or White can obtain an endgame advantage with 5.gxf3 dxe5 6.Qxd8+ Kxd8 7.f4{{chesspunc|+/−}} [[Géza Maróczy|Maróczy]]<ref name="2C_note7">Matanović 1981 (Vol C), p. 196, n. 7.</ref>) 5...dxe5 6.Bc4 giving White the advantage of the {{chessgloss|bishop pair}} in an open position as well as a large {{chessgloss|development}} 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 "[[Morphy versus the Duke of Brunswick and Count Isouard|Opera Game]]", where Morphy as White refrained from taking the b7-pawn and retained a strong {{chessgloss|initiative}} 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).<ref name=2C_note7 />