Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. d4/3...exd4/4. Nxd4/4...Bc5

Classical variation C45 Scotch game → 4. Nxd4 4...Bc5 · Classical variation In the classical continuation of the Scotch, 4...Bc5 attacks White's central knight and puts indirect pressure on the f2 square. White has three continuations of roughly equal popularity. 5. Be3 defends the knight and relieves the pressure on f2. It threatens a tactic to win a piece: if, say, 5...Nf6?? 6. Nxc6! (trades with tempo on Black's queen) dxc6 7. Qxd8+ Kxd8 8. Bxc5 wins a bishop. The main move is 5...Qf6, adding pressure to f2 and another attacker to White's knight, which White defends with 6. c3. 6. Nb5?!, the Blumenfeld attack, which threatens Nxc7+ to win the rook, is inferior due to the continuation 6...Bxe3 (threatening 7...Qxf2#) 7. fxe3 Qh4+ 8. g3 Qxe4, and if 9. Nxc7+ Kd8 10. Nxa8 White's knight is trapped and Black can pick up a rook themselves with 10...Qxh1. 5. Nxc6 trades off the knight immediately with tempo on the queen. As 5...dxc6?! allows a queen trade where Black loses castling rights, the main move is 5...Qf6, called the intermezzo variation, which threatens 6...Qxf2#. Finally, 5. Nb3, the Potter variation, saves the knight while winning a tempo on Black's bishop. Other ways to save the knight are less accurate and allow Black to build on their lead in development. 5. Nf5 sets a trap: 5...Nf6? 6. Nxg7+ Kf8 7. Bh6, threatening 8. Ne6+ winning the queen. However, it is losing to 5...d5, intending 6...Bxf5 and extending Black's development lead. 5. c3 defends the knight but doesn't develop a piece. Though this looks like it would transpose to the main line after 5...Qf6 6. Be3, Black has other options including attacking the e4 pawn and taking advantage of the fact that White can no longer play Nc3 to defend it: 5...Qh4 or 5...Nf6. 5...Qh4 6. Bd3 Nxd4 7. cxd4 Bxd4 8. O-O, Black is up a pawn. Theory table 5. Be3 Qf6 6. c3 Nge7 7. Bc4 Classical variation + 5. ... ... 6. Nb5 Bxe3 7. fxe3 Qh4+ 8. g3 Qxe4 9. Nxc7+ Kd8 10. Nxa8 Qxh1 Blumenfeld attack - 5. ... Nf6?? 6. Nxc6 dxc6 7. Qxd8+ Kxd8 8. Bxc5 (illustrative trap) 5. Nxc6 Qf6 6. Qf3 bxc6 7. Nc3 Qxf3 8. gxf3 Intermezzo variation + 5. Nb3 Bb6 6. Nc3 Nf6 7. Qe2 O-O 8. Bg5 Potter variation + 5. Nf5?! Nf6?? 6. Nxg7+ Kf8 7. Bh6 Kg8 (illustrative trap) ++ 5. c3?! Qh4!? 6. Bd3 Nxd4 7. cxd4 Bxd4 8. O-O References See also Scotch Game, Classical Variation