Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. c3/3...Nf6

3...Nf6, the Jaenisch counterattack, is Black's most popular retort to the Ponziani and most serious alternative to 3...d5. Nf6 targets White's e4 pawn, taking advantage of the fact that White cannot play Nc3 to defend it.

White may continue with 4. d4. This offers Black their choice of central pawns to take (4...Nxe4 or 4...exd4), after which White intends to push their other pawn to gain tempo and recover the pawn.

4. d3 to defend e4 is playable, but leaves White's pawn on c3 looking out of place and allows Black to take the centre with 4...d5. No other reply for White seems credible.

Carl Jaenisch recommended this reply in his 1842 book of analysis.^[1] Jaenisch gives the lines 1. e4 e5 2. Nf3 Nc6 3. c3 Nf6 4. d4 Nxe4 5. dxe5 (or 5. d5 Nb8 6. Bd3 Nf6 7. Nxe5 Bc5 8. O-O O-O 9. c4 d6 10. Nf3 Bg4 11. Nc3 Nbd7) d6 6. Bf4 dxe5 7. Qxd8+ Nxd8 8. Bxe5 Bc5.

Jaenisch discounted 3...d5 on account of 4. Bb5 and the "weakness" of Black's knight on c3. (Modern evaluation doesn't agree with his assessment of 4. Bb5?: Jaenisch seems to have missed, after 4...dxe4 5. Nxe5 to increase pressure on c6, that Black has 5...Qg5!, a double attack on e5 and g2. Today 2...d5 is one of the main ways for confront the Ponziani, and 4. Qa5 is White's most accurate reply).

1. e4 e5 2. Nf3 Nc6 3. c3 Nf6

Wikipedia has related information at Ponziani Opening.

• Taylor, Dave; Hayward, Keith (2010). Play the Ponziani. London: Everyman Chess. ISBN 1 8574 4620 8.