Chess Opening Theory/1. a3

1. a3 · Anderssen's Opening
This opening move does little for development or control of the center. In some cases, White can transpose the game to an opening where 1. a3 might have been useful, but using a tempo on such a move already on move one seems premature. In fact, this opening is based on the idea that White is playing with the black pieces, but he has the move 1. a3 already played. If a game starts 1. a3 e5 2. e4 Nf6 3. Nc3, Black cannot proceed in Ruy Lopez-fashion, and if Black plays 3... Bc5, then 4. Nf3 puts Black into the Two Knights' Defence and White's a3 precludes many possibilities.

Named after the German chess player Adolf Anderssen, who played this opening a few times against Morphy, this is a prophylactic waiting move that allows Black to choose an opening down a tempo, should a3 be useful in such cases.

Black's responses
There are a variety of ways for Black to respond to this move, including:


 * 1... e5 may transpose into an English (1. c4 e5 2. a3), where a3 is a useful move for White. It covers and prepares b4, and allows White to set up a structure similar to that in the Najdorf or Kan for Black.
 * 1... d5 makes transpositions into the Polish Opening or a reversed Pirc highly likely, should White eventually play b4 or d3/g3.
 * 1... g6 may thwart White's plans if they planned to play b4 and Bb2 as the a1-h8 diagonal would be first occupied by a black Bg7 in that case, provided that Black fianchettos their bishop immediately.
 * 1... c5 may transpose into an a3 Sicilian, or White may play b4 and attack c5.
 * 1... Nf6 will likely transpose into other aforementioned lines.

Statistics
Approximate chances

White win 30%, Draw 39%, Black win 31%.