Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bc4/3...Nf6

Two knights defence
	a b c d e f g h 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 a b c d e f g h
	Position in Forsyth-Edwards Notation (FEN) r1bqkb1r/pppp1ppp/2n2n2/4p3/2B1P3/5N2/PPPP1PPP/RNBQK2R
	Moves: 1. e4 e5 2. Nf3 Nc6 3. Bc4 Nf6
	ECO code: C55
	Parent: Italian game

3...Nf6 · Two knights defence

With 3...Nf6, Black develops a knight and attacks the e4-pawn, getting one step closer to castling.

White has several ways to proceed from this position: defend the e-pawn, usually with 4. d3, attack f7 with the aggressive 4. Ng5 (taking advantage of the fact that Black's move 3...Nf6 blocked the queen's control of the g5-square), or sacrifice the pawn for an open centre and swift attack.

Defend e4

The e4-pawn is attacked, so the most logical move for white would be to defend it.

4. d3 is the most common move, defending the pawn and opening the c1-h6 diagonal for the dark squared bishop. This is known as the modern bishop's opening. After 4...Bc5 this transposes into the Giuoco Pianissimo. 4...Be7 continues with Ruy Lopez-style development.

4. Nc3 transposes into the Italian variation of the four knights opening. Though this looks promising as it defends e4 while also developing a piece, it is less common and allows Black to play a centre fork trick. 4...Nxe4 5. Nxe4 d5 6. Bd3 dxe4 7. Bxe4 Bd6: Black temporarily sacrifices a piece in order to play d5 and get back the piece with a comfortable position and has equalised.

Attack f7

4. Ng5!? is a sideline but the most common amateur move. This Romantic move is an attack on f7 with the bishop and knight, taking advantage of the fact that Black gave up control of g5 and cannot castle yet. However, it is unprincipled to attack before having finished development and Black equalises with best play.

The most serious continuation is 4...d5, sacrificing a pawn to relieve the pressure on f7, 5. exd5 Na5, the Polerio defence which counter-attacks the bishop.

4...Bc5? is the venomous but objectively dubious Traxler counterattack. Black can answer 5. Nxf7? Bxf2+! 6. Kxf2 Nxe4+=, but instead 5. Bxf7+ is a free pawn.

In a sense 4. Ng5 also defends e4, because 4...Nxe4? (called the Ponziani-Steinitz gambit) is answered by 5. Bxf7+! Ke7 6. d4.

Sacrifice e4

4. d4, called the open variation, opens up the centre. This almost always transposes into the Scotch gambit, 4...exd4, and the main moves are 5. O-O or 5. e5. If 4...Nxe4? there is a trap, 5. dxe5 Bc4?? 6. Qd5!, threatening Qxf7# to pick up the knight.

White can also gambit the e4-pawn with 4. O-O?, intending to meet 4...Nxe4 with 5. Nc3 Nxc3 6. dxc3. White has sacrificed the pawn for a rapid lead in development and an open position, hoping for a swift attack on Black's uncastled king.

History

This line has historically also been known as the Prussian defence.^[1]

Theory table

1. e4 e5 2. Nf3 Nc6 3. Bc4 Nf6

	4	5	6	7	8	9	10	11
Giuoco piano (by transposition)	d3 Bc5
Polerio defence	Ng5 d5	exd5 Na5	Bb5+ c6	dxc6 bxc6	Bd3 Nd5	Nf3 Bd6
Fried liver attack	... ...	... Nxd5	Nxf7 Kxf7	Qf3+ Ke6	Nc3 Nb4	O-O c6
Ulvestad variation	... ...	... b5	Bf1 Nd4	c3 Nxd5
Fritz variation	... ...	... Nd4	c3 b5	Bf1 Nxd5	Ne4 Qh4	Ng3 Bg4	f3 e4	cxd4
Ponziani-Steinitz gambit	... Nxe4	Bxf7+ Ke7	d4
Traxler counterattack	... Bc5	Bxf7+ Ke7	Bd5 Rf8	O-O d6	c3 Bg4	Qb3 Bb6	Bxc6 bxc6	h3 h6
Open variation	d4 exd4	e5 d5
Scotch gambit (by transposition)	... ...	O-O
Four knights game, Italian variation (by transposition)	Nc3

References

↑ Lasker, Emanuel (1927). Lasker's Manual of Chess. New York: E P Dutton & Co. pp. 52–3.