After 1.e4 e5 2.d4 exd4, continuations than 3.Qxd4 are possible, including
transpositions to other openings.
Danish Gambit: 3.c3 3.Nf3 or 3.Bc4 Postponing recapture of the queen pawn is a standard idea in the Scandinavian Defense (1.e4 d5 2.exd5 Nf6), but 3.Nf3 is less commonly played after 2...exd4. Black can safely transpose to the
Scotch Game,
Petrov's Defense or the
Philidor Defense, or play 3...c5 4.Bc4 b5 (the Kieseritzky Variation) or a line recommended by
Alexander Alekhine, 3...Bc5 4.Nxd4 Nf6 and now 5.e5 would be met with 5...Qe7. Similar ideas are possible after 3.Bc4, which is also uncommon. 3.Bc4 is referred to in older chess works as the
Center Gambit.
Halasz Gambit: 3.f4 The Halasz Gambit, 3.f4, is another rare try. Although the move dates back to at least 1840, it has been championed more recently by the Hungarian
correspondence player Dr. György Halasz. The
gambit has been described as dubious but it has not been definitively refuted. ==References==