Chess Opening Theory/1. e4/1...d5/2. exd5/2...Nf6/3. d4

With 3. d4, White focuses on controlling as much of the centre as they can, and opens lines to develop their queen and queen's bishop.

This offers back the pawn, and Black's main continuation is to take it with 3...Nxd5, the Marshall variation. White usually plays Nf3 and c4, securing control over the centre and Black can end up cramped. If 3...Qxd5 instead, play may transpose into the Scandinavian main line after 4. Nc3 Qa5.

3...Bg4 is the Portuguese gambit. It is a gambit for Black in that Black has chosen not to recapture on d5. Therefore White has chance to defend the d5 pawn instead (e.g. 4. f3 Bf5 5. c4). Though the superficial threat of ...Bxd1 is easily parried (4. Nf3 or 4. f3 are both played), Black hopes to develop quickly and benefit from more active piece placement. If Black wishes to challenge the troublesome d5 pawn and release their king's bishop into the game, they may now play ...e6 without fear of trapping their queen's bishop.

With 3...g6!?, the Richter variation, Black prepares to fianchetto their king's bishop, as White's control of the centre makes it hard to imagine developing it along the a3-f8 diagonal. This also gives White the chance to secure the d5 pawn, 4. c4.

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

1. e4 d5 2. exd5 Nf6 3. d4

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Wikipedia has related information at Scandinavian Defense.