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

King's Knight Opening
	Position in Forsyth-Edwards Notation (FEN) rnbqkbnr/pppp1ppp/8/4p3/4P3/5N2/PPPP1PPP/RNBQKB1R b
	Moves: 1. e4 e5 2. Nf3
	Responses: ; 2...Nc6; 2...Nf6 - Petroff Defence; 2...d6 - Philidor's Defence; 2...f5 - Latvian Gambit; 2...d5 - Elephant Gambit; 2...c6 - Gunderam Gambit; 2...Qe7 - Gunderam Defence; 2...c5 - Jalalabad Gambit; 2...Qf6 - Greco Defence; 2...Bb4 - Billy Gambit; 2...Ne7 - Colman Gambit; 2...Qh4 - Mayet Gambit; 2...Qg5 - Joseman Gambit; 2...a6 - Flekon Gambit; 2...Ke7 - Reversed Bongcloud;

2. Nf3 - King's Knight Opening

After 1. e4 e5 2. Nf3, White has initiated one of the most classical and popular chess openings, the King's Knight Opening. No matter which opening White chooses, the goal is to develop their pieces quickly and control the center of the board. White should also be aware of Black's counterplay and be prepared to defend against it. With their first two moves, White demonstrates fundamental principles of chess opening play, including control of the center, development of pieces, and preparation for castling.

Control of the Center: The move 1. e4 claims central space and opens lines for the queen and king's bishop. The question for Black at this point is whether to challenge the opposing pawn on e4 or support their own pawn on e5. The follow-up 2. Nf3 develops a knight to its most active square, attacking the e5 pawn and further exerting control over the center.
Importance of Flexibility: While these are standard plans, White must remain flexible and adapt to Black's responses, tailoring the strategy to the specific position on the board.
Strategic Goals for White: In all these variations, White's objectives include rapid piece development, king safety (usually through castling), maintaining or increasing central control, and creating opportunities for tactical or positional advantages in the middlegame.

Responses by Black: Supporting the black pawn

Black's valuable center pawn is threatened with capture, but White's pawn remains safe. Black's typical response to 2. Nf3 is either 2...Nc6, defending the e5-pawn, or 2...Nf6, challenging White's e4 pawn (the Petrov Defense). Each choice leads to different types of positions and strategies.

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

2...Nc6 (King's Knight, main line)

2...Nc6 is the natural move, combining defence of the pawn with control of the d4 square and avoiding committing another pawn for now. 2. Nf3 is 10 times more popular than everything else combined, and in turn the reply 2...Nc6 is about 5 times more popular than everything else combined.

Common Continuations for White after 1. e4 e5 2. Nf3 Nc6:

3. Bb5 (Ruy Lopez): A classical approach aiming to exert pressure on Black's center and knight on c6.
3. Bc4 (Italian Game): Targets f7, the weakest point in Black's camp, and supports White's central pawns.
3. d4 (Scotch Opening): Aiming for rapid development and opening of the center.
3. Nc3 (Three Knights' Opening): Develops another piece while keeping central tension.
3. c3 (Ponziani Opening): Prepares to support the d4 push, challenging Black's central pawn structure.

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

2...d6 (Philidor)

2...d6, Philidor's Defence, is the other safe option to defend the pawn.

It restricts Black's dark-squared bishop to the e7-square, and grants White an advantage in territory, but it builds a fortress that cannot be easily battered down. This is generally considered an inferior way to defend the e5 pawn because white can easily push for advantage here, and white gets a 58% score here, with 41% wins opposed to Black's 25%. This is especially the case if Black makes a ...c7-c5 push to kick a potential knight on d4, greatly weakening the d6-pawn.

An alternative (older) way to play this is to follow up with 3...f5, but more recent analyses have proven this line to be completely losing for Black

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

2...f6? (Damiano)

Note that 2...f6? is a bad move.

2...f6 is known as the Damiano Defence. It is a poor move as it weakens black's kingside and deprives the knight on g8 of its most natural development square. Additionally, it does not even defend the pawn; if 2...Nxe5, fxe5 allows Qh5+, after which black either loses a rook (3... g6 4. Qxe5+) or is hunted into the center of the board with 3...Ke7 4. Qxe5+. Even the person for who the "defence" is named after, Pedro Damiano, condemned the defense as weak and inferior.

Challenging the White pawn

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

2...Nf6 (Petrov)

2...Nf6 is the Petrov Defence.

Black wants the same things that White wants, but once again White will be back in a symmetrical position with the advantage of moving first. This opening is known to be notoriously drawish due to the resultant symmetric positions.

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

2...f5 (Latvian Gambit)

2...f5 is the Latvian Gambit.

This iconic counter-thrust divides opinion like very few other openings.

Has Black lured White into a minefield of tricks and traps leading to an inevitable violent death?

Or has Black given away a pawn for nothing?

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

2...d5 (Elephant Gambit)

2...d5 is the Elephant Gambit.

It's along the same lines as the Latvian, but less complex – White needs to do less memorising to reach a good position.

Statistics

Estimated next move popularity.

Nc6 83.5%, Nf6 11%, d6 4%, f5 0.5%, other less than 0.5%.

Theory table

For explanation of theory tables, see theory table and for notation, see algebraic notation.

1. e4 e5 2. Nf3

	2	3	4	5
Ruy Lopez	... Nc6	Bb5 a6	Ba4 Nf6	O-O Be7	=
Petrov's Defence	... Nf6	Nxe5 d6	Nf3 Nxe4	d4 d5	=
Philidor Defence	... d6	d4 exd4	Nxd4 Nf6	Nc3 Be7	+=
Latvian Gambit	... f5	Nxe5 Qf6	d4 d6	Nc4 fxe4	+/-
Elephant Gambit	... d5	exd5 Bd6	d4 e4	Ne5 Nf6	+=
Câmara Defence	... Qe7	Bc4 d6	O-O g6	d4 Bg7	+=
Greco Defence	... Qf6	Bc4 Qg6	Nc3		+/-
Damiano Defence	... f6?	Nxe5!			+/-

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Wikipedia has related information at King's Knight Opening

References

Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.

Nunn's Chess Openings. 1999. John Nunn (Editor), Graham Burgess, John Emms, Joe Gallagher. ISBN 1-8574-4221-0.

Panov, Vasily (1973). Teoría de Aperturas, Tomo I: Aperturas Abiertas - Aperturas Semiabiertas. ISBN 84-270-0132-0.
Schiller, Eric (2002). Standard Chess Openings. ISBN 1-58042-048-6.