King's Pawn Game

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White opens with the most popular of the twenty possible opening moves. Although effective in winning for White (54.25%), it is not quite as successful as the four next most common openings for White: 1.d4 (55.95%), 1.Nf3 (55.8%), 1.c4 (56.3%), and 1.g3 (55.8%).^[2] Since nearly all openings beginning 1.e4 have names of their own, the term "King's Pawn Game", unlike Queen's Pawn Game, is rarely used to describe the opening of the game.

Advancing the king's pawn two squares is highly useful because it occupies a center square, attacks the center square d5, and allows the development of White's king's bishop and queen. Chess grandmaster Bobby Fischer said that the King's Pawn Game is "Best by test",^[3] and proclaimed that "With 1.e4! I win."^{[4][page needed]}

King's Pawn Games are further classified by whether Black responds with 1...e5 or not. Openings beginning with 1.e4 e5 are called Double King's Pawn Games (or Openings), Symmetrical King's Pawn Games (or Openings), or Open Games – these terms are equivalent. Openings where Black responds to 1.e4 with a move other than 1...e5 are called Asymmetrical King's Pawn Games or Semi-Open Games.

The Encyclopedia of Chess Openings (ECO) classifies all King's Pawn Games into volumes B or C: volume C if the game starts with 1.e4 e6 (the French Defence) or 1.e4 e5; volume B if Black answers 1.e4 with any other move. The rare instances where the opening does not fall into a more specific category than "King's Pawn Game" are included in codes B00 (includes the Nimzowitsch Defence and unusual moves after 1.e4), C20 (includes Alapin's Opening and unusual moves after 1.e4 e5), C40 (includes the Latvian Gambit and unusual moves after 1.e4 e5 2.Nf3), and C50 (includes the Hungarian Defence, the Giuoco Pianissimo, and unusual moves after 1.e4 e5 2.Nf3 Nc6 3.Bc4).

The Black responses which are given one or more chapters in the Encyclopedia of Chess Openings (ECO) are given below, ranked in order of popularity according to ChessBase.

Apart from these eight responses, all other replies from Black are covered together in ECO chapter B00 ("Uncommon King's Pawn Opening"). A few of these are not entirely obscure, and have received extensive analysis.

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