Open games or Double King Pawn games are chess openings where the first moves are 1 e4 e5. They are by far the most popular opening two moves. They are popular, because they are strong moves. We will examine these moves and the open game openings that fall under them in some detail. Open games are classed in ECO codes C20-C99.
1 e4 advances the White's King's pawn two squares. By doing so it fulfills several requirements of opening theory; control of center and rapid development of pieces. Pawn stakes a claim to center and by freeing the e2 square its clears a path for both the Bishop and the Queen to develop. On the other hand the move e4 weakens the points, d4 and f4, and the pawn on e4 is as yet undefended. By 2... e5 Black creates a mirror image of White's position with the same advantages and disadvantages. We are now in an Open Game
Now White has several second move options to choose from and most of them give rise to various popular openings.
By far the most used is the 2. Nf3. This aims at attacking the Black's central e5 pawn, prepares for pawn advance to d4, develops the Knight to its best square, and clears a square for King side castling, all which are comply with sound opening principles.
After 2 Nf3
Black also has several choices after 2. Nf3. Most used is 2 ... Nc6 defending the pawn and center and developing a piece. After that if White plays 3 Bb5 the game enters Ruy Lopez or Spanish opening. After 2 ... Nc6 2 d4, the opening is called Scotch Game, and after 2 ... Nc6 3. Bc4 it is the Italian Game. Another possibility is Four Knights Game after Nc6 3 Nc3 Nf6.
If Back chooses to play 2 ... Nf6 instead of Nc6 maintaining the mirror image the opening is called Petrov's Defense. Another possibility for Black is 2 ... d6 starting the Philidor Defense. Although it is a solid defense Philidor Defense is not popular nowadays because it tends to restrict the Black's mobility and ability to take the initiative, and allows White more space. All other responses to Nf3 are not recommended.
Alternatives to 2 Nf3
We will now consider White's valid alternatives second moves in an Open game. 2 Nc3 starts the Vienna Game, 2 Bc4 will lead to Bishop's Opening, and 2 f4 will start the King's Gambit. All three openings mentioned lead to similar positions and in some cases of Bishop's Opening to identical positions to Vienna Game. Vienna Game usually includes the f4 advance in the King's Gambit in order to attack the Black center. King's Gambit aims for rapid development and weakening of Back center by a pawn sacrifice.
Another possible second move is 2 d4, the Center Game. This leads to 2 ... exd4 3 Qxd4. White will have open a center and a prematurely developed Queen. He can avoid the pre mature development of Queen by playing the Danish Gambit 2 ... exd4 3 c3 sacrificing pawns for open center.
These are the main openings that come under the Open Game. Of other possibilities for White in Open Games, Parham Attack (2.Qh5), Napoleon Opening (2.Qf3), are very bad and Portuguese Opening (2.Bb5), Alapin's Opening (2.Ne2), Konstantinopolsky Opening (3.g3), and Inverted Hungarian Opening (3.Be2) are very risky and rarely met with in master play except as experimentations. In case of Black, Damiano Defense (2...f6) is consider very bad, while Elephant Gambit (2...d5) and Latvian Gambit (2...f5) are considered highly risky.
