Open Game

An Open Game (or Double King's Pawn Opening) is a generic term for a family of chess openings beginning with the moves:

1. e4 e5

When Black maintains symmetry by replying 1...e5, controlling the central square d4, the result is an Open Game.¹² The resulting position gives rise to many of the oldest and most deeply analyzed openings in the game. Play tends to continue 2.Nf3 Nc6, leading to the Ruy Lopez (3.Bb5), Italian Game (3.Bc4), Scotch Game (3.d4), and others. Black's most important alternative to 2...Nc6 is 2...Nf6, Petrov's Defense. Other Open Games include the King's Gambit (2.f4) and Vienna Game (2.Nc3).

Other responses to 1.e4 can be classified as Semi-Open Games or Single King's Pawn Games. When written in lowercase, the term "open game" refers to a chess position where ranks, files and diagonals are open, and tending to more tactical gameplay. It is possible that an Open Game may lead to a closed game.¹ For example, the Italian Game is an Open Game where White frequently plays d3, intending to keep the game closed, while the Sicilian Defence (1...c5), a Semi-Open Game, is frequently opened via 2.Nf3 and 3.d4 cxd4 4.Nxd4, known as the Open Sicilian.

After having been the most common response to White's most popular first move e4 until the mid-20th century, 1...e5 remains the second most popular top-level response to 1.e4 (1...c5 is slightly more popular among tournament players).³ 1.e4 e5 is often among the first openings taught to new players.⁴

1.e4 immediately stakes a claim in the center and frees two pieces (the queen and king's bishop) for development. Bobby Fischer wrote that 1.e4 is "Best by test."⁵ On the negative side, 1.e4 places a pawn on an undefended square and weakens the squares d4 and f4. The symmetrical 1...e5 incurs the same strengths, but also the same drawbacks, for Black: White's usual response 2.Nf3 attacks the undefended pawn. Along with the Sicilian Defence (1...c5), it is the most extensively analyzed of Black's responses to 1.e4. Compared to 1...c5, the other most common response to 1.e4, 1...e5 results in more draws; in particular, there are the drawing weapons of the Berlin Defence (2.Nf3 Nc6 3.Bb5 Nf6) and Petrov's Defence (2.Nf3 Nf6). However, there are many less drawish alternative lines for both sides.

The most popular second move for White is 2.Nf3 (the King's Knight Opening), attacking Black's king pawn, preparing to castle kingside, and preparing for d2–d4 in many lines. Black's usual reply to 2.Nf3 is 2...Nc6, defending the king's pawn without restricting the movement of the king's bishop. From here several named openings can arise.

The Ruy Lopez or Spanish Game (3.Bb5) is one of the most popular openings at all levels of chess, and one of the most extensively analyzed. Black's most common response is 3...a6, forcing White to make a decision between exchanging the bishop for the knight with 4.Bxc6 or retreating with 4.Ba4. Also common is 3...Nf6, the Berlin Defense. Black has several alternatives, the sharpest of which is the Jaenisch Gambit or Schliemann Defense, 3...f5.

The Italian Game (3.Bc4) is White's second most popular move, usually leading to either the Giuoco Piano (3...Bc5) or the Two Knights Defense (3...Nf6). The name "Italian Game" is also used as a synonym for the Giuoco Piano by many writers. A sharp continuation to the Giuoco Piano is the Evans Gambit (4.b4), offering a pawn for a lead in development and attacking chances.

The Scotch Game (3.d4) was popular in the 19th century and is still the third most common move. After the usual 3...exd4, White may either recapture with 4.Nxd4 with an approximately equal game, or play the Scotch Gambit (4.Bc4), a risky but dangerous tactical line against an unprepared opponent.

The Four Knights Game (3.Nc3 Nf6) was also quite popular in the 19th century. It frequently leads to positional games and is generally considered less challenging for Black to defend against than the three lines above. Less commonly after 3.Nc3, 3....g6 or 3...Bb4 (the Three Knights Game) are possible.

The Ponziani Opening (3.c3) has never achieved widespread popularity but is occasionally used as a surprise weapon. Other third moves for White such as the Konstantinopolsky Opening (3.g3)⁶⁷ and Inverted Hungarian Opening (3.Be2) are rarely played and offer White no advantage.

Black's most important alternative to 2...Nc6 is 2...Nf6, known as Petrov's Defense or Russian Defense. It is a common opening in high level play, where it has a reputation as a drawing weapon. White can avoid the extensive theory of the Petrov by playing 3.Nc3, which could transpose into a Four Knights Game after 3...Nc6. Another possibility is 3... Bb4.

The Philidor Defense (2...d6) defends the pawn on e5 but has the disadvantage of restricting the mobility of Black's king's bishop, and typically leads to solid but passive positions for Black. For this reason, it largely fell out of favor by the early 20th century as Black players sought more dynamic options, but it has a dependable reputation and is still occasionally seen at grandmaster level.

The Elephant Gambit (2...d5) and the Latvian Gambit (2...f5) are considered very risky for Black. The Gunderam Defense (2...Qe7) is an offbeat choice which blocks the development of the king's bishop and has never achieved widespread popularity. The Damiano Defense (2...f6) may be met by either 3.Nxe5 or 3.Bc4 with advantage and is almost never seen. The Busch–Gass Gambit (2...Bc5), which was something of an online fad in the early 2020s, is well met by 3.Nxe5 Nc6 4.Nf3.

The most popular alternatives to 2.Nf3 are 2.f4 (the King's Gambit), 2.Nc3 (the Vienna Game), and 2.Bc4 (the Bishop's Opening). The King's Gambit was popular before the 20th century with master and amateur alike. White offers a pawn to undermine Black's center and achieve quick development. The Vienna Game also frequently features such attacks on the Black center by means of f2–f4. Some of its lines, as well some in the Bishop's Opening, can transpose to variations of the King's Gambit.

In the Center Game (2.d4), White immediately opens the center, though if the pawn is to be recovered after 2...exd4 with 3.Qxd4, Black may gain a tempo on White's queen with 3...Nc6. An alternative is to sacrifice one or two pawns by offering the Danish Gambit (3.c3).

The early development of the queen in the Danvers Opening (2.Qh5, also known as the Parham Attack) is usually played only by amateurs, though Hikaru Nakamura has experimented with it in grandmaster tournaments and was able to achieve a reasonable position.⁸⁹ The Napoleon Opening (2.Qf3) has even less to recommend it as Black can easily block any mating threats without compromising their development. The Portuguese Opening (2.Bb5) and Alapin's Opening (2.Ne2) are offbeat tries for White, but neither gain any advantage against correct play. The Bongcloud Attack (2.Ke2) is considered a joke opening.