Two Knights Defense

The Two Knights Defense (also called the Prussian Defense) is a chess opening that begins with the moves: 1. e4 e5 2. Nf3 Nc6 3. Bc4 Nf6 Black's third move threatens to capture White's pawn on e4. First recorded by Giulio Cesare Polerio in c. 1580, White’s traditional and most direct approach is 4.Ng5, threatening Black’s f-pawn, defended only by the king. The theory of this opening was extensively developed in the 19th century, when Mikhail Chigorin demonstrated Black's compensation in the line 4.Ng5 d5 5.exd5 Na5 6.Bb5+ c6 7.dxc6 bxc6, where Black gambits a pawn for a lead in development. White also frequently plays 4.d3, a more positional continuation often transposing to the Giuoco Pianissimo, or 4.d4, usually transposing to the Scotch Gambit. The Two Knights is a more aggressive continuation than the Giuoco Piano (3...Bc5), which avoids the 4.Ng5 line. David Bronstein argued that the term "defense" doesn't capture the opening's true character and suggested "Chigorin Counterattack" as a more appropriate name. The Two Knights Defense has been played and analyzed by many aggressive players, including Chigorin, Paul Keres, and world champions Mikhail Tal and Boris Spassky.