Chess Opening Theory/1. e4/1...e6/2. d4/2...d5/3. Nc3/3...Nf6/4. Bg5/4...Be7

Classical variation
a b c d e f g h 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1 a b c d e f g h
Position in Forsyth-Edwards Notation (FEN) rnbqk2r/ppp1bppp/4pn2/3p2B1/3PP3/2N5/PPP2PPP/R2QKBNR w
Moves: 1. e4 e6 2. d4 d5 3. Nc3 Nf6 4. Bg5 Be7

Classical variation

Because Nf6 is no longer pinned, Black threatens to win the e4-pawn.
The attempt to defend the e4-pawn, e.g. by 5.f3?! or 5.Bd3?!, will still lose the pawn, because White's Bg5 is not defended, so Black can simply play 5...Nxe4! and win a pawn (6. Bxe7 Nxc3 7. Bxd8 Nxd1 8. Bxc7 Nxb2 -/+).
That's why White either plays the e4-pawn to a safe square (Main Line - 5.e5), or eliminates an attacker of e4 (5.Bxf6). A safe alternative is a transposition to the Exchange Variation (5.exd5).

Theory table

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

1. e4 e6 2. d4 d5 3. Nc3 Nf6 4. Bg5 Be7
	5
Main Line	e5	=
1	Bxf6	=
2	exd5	=

References

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