Semi Open Games or Single King Pawn Games are chess openings where the White's first move 2 e4 is followed by any other move than symmetrical 2 … e5. They include some of the most popular openings in chess.
In Semi-open events in reply to White's e4, which stakes a claim on central squares and open lines for White's Bishop and Queens, Black give up any attempt to create a mirror image by playing e5. Instead Black can take several other routes. The theory and ideas behind each of these Semi open openings can be quite varied.
For instance the Sicilian Defense (1 … c5) creates an unbalanced situation on the board, allowing both players excellent playing possibilities and chances for Black to seize the initiative. This explains that opening of high popularity.
French Defense accepts a certain lack of mobility in exchange for solidarity. The first move reply in French Defense is 1 … e6, usually followed by 2.d4 d5.
In Caro-Kann Defense, were 1 … c6 is usually followed by 2 d4 d5, Black will try to use the c pawn to bolter the strong point at d5 and develop the Queen side Bishop. In contrast Scandinavian Defense (1 … d5) also called Center Counter Defense invites an immediate tactical fight for the center.
Semi-open openings like Alekhine's (1 … Nf6), the Pirc (1.e4 d6 2.d4 Nf6 3.Nc3 g6) and the Modern defense (1.e4 g6) all operate under hypermodern opening theory, which after allowing White to create an extended center unhindered by Black pawns, aim to attack it with pieces from a distance.
Other valid Semi-open events include Nimzowitsch Defense and Owen's Defense. Nimzowitsch Defense (1 … Nc6) tries to steer the game into obscure lines of play condemning White clear targets. Owen's Defense (1 … b6) with an early fianchettoed Bishop, allows White to create a center and then attack it from wings. Black must be on constant vigilance in this opening
When it comes to popularity, by far the most popular of Semi-open openings is the Sicilian defense, followed closely by the French Defense and the Caro-Kann Defense. The Pirc Defense and Modern Defense also see a great deal of tournament exposure, while Alekhine's Defense and Scandinavian Defense make regular appearances in tournament play. Owen's Defense and Nimzowitsch Defense while valid Semi-open openings do not get much tournament play these days. Experimental possibilities exist for Grob Defense (1 … g5) and St.. George Defense (1 … a6).
ECO codes for semi open openings are, C00 to C19 for 1.e4 e6 or French Defense, B20 to B99 for 1 e4 c5, Sicilian Defense, and B00 to B19 for 1 e4 followed by any other move than 1 … c5, 1 … e6, 1 … e5.