411 REFERENCE · Wikibooks
Chess Opening Theory/1. e4/1...e6/2. d4/2...d5/3. Nd2/3...Nf6/4. e5
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Closed Tarrasch C05 French defence → Tarrasch → Closed Tarrasch
4. e5
White takes space, closes up their position and defends their e-pawn. Black plans to attack White's pawn chain at either end, with the c-pawn and the f-pawn, but first they must prevent their knight from falling.
Black should retreat it by playing 4...Nfd7.
4...Ne4?! is occasionally tried, but after 5. Nxe4 dxe4 Black's pawn on e4 is permanently weak.
Theory table
all Closed Tarrasch 4. ... Nfd7 5. Bd3 c5 6. c3 Nc6 7. Ne2 cxd4 8. cxd4 f6 9. exf6 Nxf6 + 4. ... ... 5. ... ... 6. ... ... 7. ... ... 8. ... Nb6 Leningrad variation ++ 4. ... ... 5. ... ... 6. ... ... 7. Ngf3 Qb6 8. O-O cxd4 9. cxd4 Nxd4 10. Nxd4 Qxd4 11. Nf3 Qb6 + 4. ... ... 5. ... ... 6. ... b6 7. Ne2 Ba6 8. Bxa6 Nxa6 9. O-O Nc7 Botvinnik variation ++ 4. ... Ne4?! 5. Nxe4 dxe4 6. dxe4 ++
References
French Defence