Since given names of chess openings are not very systematic other methods of classification has to be adapted for study and analysis purposes. The most common methods of such systematic classification class the openings according to the actual opening moves made.
From the opening position White can make twenty moves. However, only a few of these moves are popular since only they are conducive to implementing the general principles of opening which advocate control of center and rapid development of pieces. Most popular moves are 1.e4, 1.d4, 1.Nf3, and 1.c4.
In addition some of the other moves while they break the opening principles can give the player certain advantages. For instance 1 Nc3 or Dunst Opening places the Knight in a good position but prevents the c pawn from advancing. 1 f4 or Bird's Opening while increasing the pressure on center weaken the King side. The 1.b4 or Sokolsky Opening and 1.b3 and 1.g3 or the Queen's and King's fianchetto Openings, aims to develop the Bishops through fianchetto but does not directly dispute the control of center using pawns.
Each move has to be analyzed to learn its strengths and weakness. After such analysis twelve of the possible opening moves are judged to result in weak positions for White and are very infrequently used in major tournaments.
In reply to White's opening move Black too can make twenty moves. Most popular Opening moves for Black are exact counterparts of the White's Opening moves. However since Black is responding to White, Black can use other opening moves advantageously as well without breaking opening principles. For instance 1...c6 and 1...e6, can be coupled with 2... d5 for good effect, or 1...d6 coupled with a fianchetto of King side Bishop.
ECO
One of the most widespread and accepted methods of classification of openings used by professional players is the classification by Encyclopedia of Chess Openings (ECO) codes. ECO uses a unique coding system to classify the opening according the opening moves. The codes are classed into five main categories, and with hundred sub categories under each of them, according to the moves. For instance, openings beginning with 1.e4 comes under categories B and C with 1.e4 e6 (known as the French Defense) under sub categories C00-C19, 1.e4 e5 (Double King Pawn) under C20-C99, 1.e4 without 1...c5, 1...e6, 1...e5 under B00-B19, and 1.e4 c5 (Sicilian Defense) under B20-B99. All the possible openings are categorized in this way.
While ECO classification is useful to serious chess players, it can be too confusing and too technical for beginners and middle level players getting to grips with chess openings. It also separate related openings with similar features under different categories. For instance, Indian Systems can be found under both A and E categories.
Simpler Classification
So for educational purposes and better understanding of the theory, a simpler opening move based classification is used. This divides the openings to three categories; King's Pawn Openings (those that start with 1.e4), Queen's Pawn Openings (1.d4), and Others.
However since this categorization is too broad it is further sub-divided. King's Pawn Openings are divided into Open or Double King Pawn Games (opening moves 1.e4 e5) and Semi-Open or Single King Pawn Games (1.e4 without 1...e5). Queen's Pawn Openings are divided into Closed or Double Queen Pawn Games (1.d4 d5), and Semi-Closed or Single Queen Pawn Games (1.d4 without d5). Openings with moves b3, b4, c4, Nf3, f4, and g3 are termed Flank openings, while the rest of the openings are classed under "Unusual openings". Sometimes Indian Systems, which begins with the moves 1.d4 Nf6, which should come under Semi-Closed Games are classed separately since their breadth and importance require such study.
