Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. c3/3...d5/4. Qa4

By pinning Black's knight on c6 to their king, 4. Qa4 undefends Black's e pawn and threatens Nxe5.

Were Black to ignore the threat and counterattack instead, 4... dxe4? 5. Nxe5! (threatens Nxc6 bxc6 Qxc6 winning at least one pawn) Qd6 6. Nxc6 bxc6 7. Qxe4+ wins a pawn.

So Black must protect the e5 pawn. Their choices are:

• 4...Bd7, the Caro gambit. Eliminates the pin. This protects the e pawn but, by obstructing queen's vision of d5, gives up Black's d pawn. After 5. exd5 Nd4 (discovered attack on the queen) 6. Qd1□ Nxf3+ 7. Qxf3 Black has equalised.

• 4...f6, the Steinitz variation. Defends e5 directly. The traditional, most Ponziani-ist reply is 5. Bb5, threatening to take the pinned knight, where the natural 5...Bd7? to interrupt the pin is greatly in White's favour. (5. Bb5 Bd7? 6. exd5 Nce7 7. Bxd7+ Qxd7 8. Qxd7+ Kxd7 ±) After 5...Nge7 to defend the knight however, 6. exd5 Qxd5 7. d4 and the position is unclear.

The modern move, advised by the engine and played by top players like Nepomniachtchi, is 5. d3 =, where White gives up on playing d4 in one move and admits that c3 looks a little disjointed now.

• 4...Nf6, allowing Nxe5 with the Leonhardt variation. Although this appears add an attacker on to White's e4 pawn, it doesn't work out that way (5. Nxe5 Nxe4 6. Nxc6 bxc6 7. Qxc6+ Bd7 8. Qxd5 Nf6 and White is up two pawns).

Instead, it acts to over-protect d5, allowing Bd4 and preparing to castle. 4...Nf6 5. Nxe5 Bd6 6. Nxc6 bxc6 and 7. Qxc6+? fails to 7...Bd7, where in this line White doesn't have 8. Qxd5.

Game may continue 7. d3 (e4 was hanging) O-O or 7. d4 Nxe4 8. Qxc6+ Bd7 9. Qxd5 O-O, where White is still up two pawns but Black has castled and has compensation in development.

• 4...Qd6 is an alternative to protect the pawn. One idea for Black's is that this allows Bd7, breaking the pin, without obstructing their queen's vision of d5. After 5. d4 Bd7 6. exd5? leads to a much better (for Black) version of the Caro gambit. 6...Nxd4 (discovered attack) 7. Qd1 Nxf3+ 8. Qxf3 O-O-O.

5. Bb5 and 5. d4 (engine's preference) have both been played. 4...Qd6 is uncommon and doesn't have a name, but was played in 1857 in Loewenthal vs Barnes, so might be called the Barnes variation.

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

1. e4 e5 2. Nf3 Nc6 3. c3 d5 4. Qa4

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Wikipedia has related information at Ponziani Opening

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