Editing Philidor Defence (section)

===Philidor Countergambit: 3...f5 <span class="anchor" id="Philidor Countergambit"></span>===
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| Philidor Countergambit: 3...f5!?
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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>