Chess Opening Theory/1. e4/1...e5/2. Nf3

King's knight opening C40 2...Nc6 · Normal variation 2...Nf6 · Russian game/Petrov 2...d6 · Philidor defence 2...f5 · Latvian gambit 2...d5 · Elephant gambit 2...Qf6 · McConnell/Greco defence 2...Qe7 · Gunderam defence Open game 2. Nf3 · King's knight opening White develops a piece to a more active square, asserts control in the centre and over the d4 square, and attacks Black's e5-pawn. This is the most common opening played in chess. Black now chooses: defend the pawn, or counter-attack? Defend Black's e-pawn Black has several ways to defend e5, with a piece or pawn. 2...Nc6 is the main line. This develops a piece while also defending e5. A key advantage of 2...Nc6 over alternative moves is that 2...Nc6 controls both e5 and d4. It is about five times more popular than everything else combined. 2...Nc6 leads into many of the most popular openings, including 3. Bb5, the Spanish or Ruy Lopez, 3. Bc4, the Italian, and 3. d4, the Scotch. 2...d6 defends e5 with a pawn. This is known as the Philidor defence, and was recommended by chess theoreticians in past centuries who wanted to avoid facing 2...Nc6 3. Bb5. This is the second most common move in amateur play, but much less common today in tournament play. The main disadvantage of defending e5 with a pawn is that, by not developing a piece instead, Black can fall behind in development. 2...d6 also makes it harder to develop Black's king side bishop: Black will have to move the g-pawn or d-pawn again to free it. Since 2...d6 doesn't help control d4, White's most critical response is 3. d4. There are a few other eccentric ways to defend e5, ranging from poor to perilously bad: 2...f6? is the other way to defend e5 with a pawn. However, for tactical reasons f6 is actually unable to defend e5 as it weakens Black's kingside too much. If 2...Nxe5 3. fxe5 allows Qh5+!, and Black either ends up losing a rook or having their king hunted into the centre of the board. It was refuted (debunked) in the 16th century by Pedro Damiano. 2...Bd6? technically develops a piece to defend the pawn, but this is a mistake for a bunch of reasons. This isn't a great place to develop the bishop to and Black will soon want to move it again: its scope (the number of squares it controls) is not much better on d6 than f8, and on d6 it blocks in Black's d-pawn. Unlike 2...Nc6, this does not help Black to control d4. 2...Qf6?, the McConnell or Greco defence, defends the e5-pawn but at the cost of preventing Black from developing their knight to f6. 2...Qf6 pressures f2: Black may hope that White will one day move their knight and blunder checkmate. 2...Qe7?! is the Gunderam defence. This blocks in Black's bishop: Black will have to move their queen again or fianchetto it with g6 and Bg7. 1. e4 e5 2. Nf3 Nc6 King's knight normal variation 1. e4 e5 2. Nf3 d6 Philidor defence 1. e4 e5 2. Nf3 f6 Damiano defence 1. e4 e5 2. Nf3 Bd6 1. e4 e5 2. Nf3 Qf6 McConnell defence 1. e4 e5 2. Nf3 Qe7 Gunderam defence Attack White's e-pawn Black can ignore the attack on their e-pawn to threaten White's instead. 2...Nf6 develops a piece while counter-attacking White's e4 pawn. This known as the Russian game, or Petrov's or Petroff's defence. White can take the e5 pawn 3. Nxe5 but Black has several ways to win it back. This opening is notoriously drawish at the highest levels due to the resultant symmetric positions. Alternatively, Black can also attack e4 with either the d or f pawn. Both of these gambits are considered dubious with best play but have the potential to outwit an unprepared opponent. 2...f5?! is the Latvian gambit. White has their choice of captures: 3. exf5 or 3. Nxe5. Both are playable, and it's up to Black to prove they have lured White into a minefield of traps, not just given away a pawn for nothing. 2...d5?! is the Elephant gambit. Again, White has their choice of captures and both 3. exd5 and 3. Nxe5 are playable. There are tactical possibilities for both sides. 1. e4 e5 2. Nf3 Nf6 Russian game 1. e4 e5 2. Nf3 f5 Latvian gambit 1. e4 e5 2. Nf3 d5 Elephant gambit Sacrifice the pawn The above continuations account for almost the entire corpus of serious, tournament games. At the amateur level, Black can of course just choose to do something completely different, including: 2...Bc5, the Busch-Gass gambit. Black sacrifices the pawn to attack f2 straight away with 3...Qh4, or with the plan of trading off the knights and opening up lines for development (3. Nxe5 Nc6 4. Nxc6 dxc6). 2...c6, the Gunderam gambit, played presumably with the idea of supporting 3...d5, but by preventing Black from playing Nc6 it invites 3. d4! exd4 4. Qxd4. 2...c5 transposes into the abysmal Jalalabad variation of the Sicilian defence. Theory table 1. e4 e5 2. Nf3 2 3 4 5 Ruy Lopez ...Nc6 Bb5a6 Ba4Nf6 O-OBe7 = Petrov's Defence ...Nf6 Nxe5d6 Nf3Nxe4 d4d5 = Philidor Defence ...d6 d4exd4 Nxd4Nf6 Nc3Be7 += Latvian Gambit ...f5 Nxe5Qf6 d4d6 Nc4fxe4 +/- Elephant Gambit ...d5 exd5Bd6 d4e4 Ne5Nf6 += Câmara Defence ...Qe7 Bc4d6 O-Og6 d4Bg7 += Greco Defence ...Qf6 Bc4Qg6 Nc3 +/- Damiano Defence ...f6? Nxe5! +/- King's Knight Opening References Panov, Vasily (1973). Teoría de Aperturas, Tomo I: Aperturas Abiertas - Aperturas Semiabiertas. 84-270-0132-0. Schiller, Eric (2002). Standard Chess Openings. 1-58042-048-6.