4.Ng5 — Knight attack in the Two Knights
4.Ng5
Definition
The algebraic notation 4.Ng5 denotes a knight move to the g5-square on a player’s fourth turn. In modern practice the term almost always refers to the position arising after the sequence 1. e4 e5 2. Nf3 Nc6 3. Bc4 Nf6 4. Ng5 in the Italian Game, Two Knights Defence. White’s king-side knight (originally on g1) has maneuvered via f3 to the aggressively posted g5 square, immediately attacking f7 and setting the stage for the celebrated Fried Liver and Lolli attacks.
Typical Opening Contexts
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Italian Game, Two Knights Defence
1. e4 e5 2. Nf3 Nc6 3. Bc4 Nf6 4. Ng5 - Occasionally in other e-pawn openings if Black imitates the Two Knights set-up, but these are rare.
Strategic Purpose
By leaping to g5, the knight unleashes a direct threat: Nxf7+, forking Black’s queen and rook and rupturing the king’s shelter. The move therefore forces Black to make a critical choice:
- 4…d5!? – the main line, striking in the center. After 5. exd5, Black can choose 5…Na5 (the aggressive Traxler Counter-Attack) or the solid 5…Nxd5 (leading to the mainline Two Knights). If Black instead plays 5…Nxd5? 6. Nxf7! is the guts of the Fried Liver Attack.
- 4…Bc5?! – the sharp Wilkes-Barre (Traxler) Variation, conceding the f7 pawn in search of counterplay against White’s king.
- Other tries—such as 4…h6 or 4…d6—are considered inferior because they allow 5. Nxf7.
Tactical Motifs
- Double attack on f7 (king & rook).
- Discovered attack ideas after d2–d4 opening the c1-bishop.
- King hunt patterns: Ke8–f7–g6 in the Fried Liver.
- Counter-sacrifice themes for Black in the Traxler.
Historical Significance
The line dates back at least to the 16th century, studied by Greco and later by Paul Morphy, who used it to crush many opponents in simultaneous exhibitions. Its romantic, sacrificial nature made it a darling of 19th-century chess, yet the move retains practical venom even with modern engines.
Illustrative Game
Paul Morphy – Duke Karl / Count Isouard, Paris 1858 (consultation game). Morphy demonstrates the power of central development over material in a famous miniature that begins 1. e4 e5 2. Nf3 Nc6 3. Bc4 Nf6 4. Ng5 and culminates in the dazzling queen sacrifice 17. Qb8+!.
Common Continuations & Theory Table (overview)
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4…d5 5.exd5
- 5…Na5 ― Mainline Two Knights (solid for Black)
- 5…Nxd5?! 6.Nxf7 ― Fried Liver (risky for Black)
- 4…Bc5!? ― Traxler / Wilkes-Barre Counter-Attack (ultra-sharp)
- 4…h6? 5.Nxf7! Kxf7 6.d4 ― Large advantage for White
Interesting Facts & Anecdotes
- In scholastic tournaments the phrase “Go for the Fried Liver” is practically synonymous with 4.Ng5, highlighting its popularity among juniors for its immediate attacking chances.
- Despite deep engine analysis, top grandmasters like Fabiano Caruana and Wesley So occasionally spring 4.Ng5 in rapid and blitz, trusting preparation and clock pressure.
- The move led to one of the most famous computer-chess upsets: Comet – Fritz, 2004. The underdog engine used 4.Ng5 to win spectacularly.