Chess Opening Theory/1. e4/1...d6/2. d4/2...Nf6/3. Nc3

White defends their e4 pawn, which was under attack, by developing their knight to its most active square. On this square the knight helps to control the centre but it does prevent White from playing c4 and prevents transposition into King's Indian games.

3...g6 is the main move, preparing to play ...Bg7 and pressure the centre with their pieces from afar, in the hypermodern style.

Alternatively Black can still choose to contest the centre with pawns.

3...e5 transposes into something like a Philidor defence, where Black has pawns on d6 and e5 and White on d4 and e4. If 4. dxe4 dxe4, this leads to queen trade and Black loses castling rights 5. Qxd8+ Kxd8. To keep queens on the board, Black can instead prepare ...e5 with 3...Nbd7. This is called the Lion defence: essentially a move order trick to play a Philidor defence where Black has avoided some critical lines.

3...c6, the Czech defence, is a sideline. Black opens a line for their queen to develop, and may yet play ...e5 or go for a "small centre" with ...e6.

1. e4 d6 2. d4 Nf6 3. Nc3

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