Opening classification is determined by the most recent book move made in a game.
If the position on the chess board is a known one from a recognized opening, the game is said to be of that type, regardless of how it got there. This is called a "transposition."
The best way to ID openings is using ECO codes, because each code refers to an exact sequence of moves. The ECO codes are precise and specific. See the links for more info that will make more sense than I can in a few sentences. Of course, if you don't use any chess software the odds are you don't use ECO codes because there's 500 of them from A00 - E99 and the software has a much better memory than most people!
http://www.chessgames.com/chessecohelp.html
http://www.365chess.com/eco.php
dont get the question
ohh......... yea ECO codes work, but I don't use them
A chess opening is defined as the "Most Specific" description that fits the moves of the game.
The "Queen's Gambit" is a very generic description. The "Slav Defense" is a subset of the Queen's Gambit. The "Queen's Gambit Declined" is more specific than Queen's Gambit, but still generic and typically used to describe 2...e6.
So think of it as follows:
1.d4 d5 2.c4 e6 3.Nc3 Nf6 4.Bg5 Be7 5.e3 O-O 6.Nf3 Nbd7 is the "Queen's Gambit Declined, Orthodox Defense"
1.d4 d5 2.c4 e6 3.Nc3 c5 is the "Tarrasch Defense"
1.d4 d5 2.c4 c6 3.Nf3 Nf6 4.Nc3 dxc4 or 4...a6 is the "Slav Defense" while 4...e6 is the "Semi-Slav Defense"
1.d4 d5 2.c4 Nc6 is the Chigorin Defense
1.d4 d5 2.c4 h6 is simple "The Queen's Gambit" because it's the most specific description for the line played as Black's second move is utter nonsense.
King's Indian Attack:
King's Indian Defense:
Thank you so much for all the responses. This definitely has answered my question. I know that at my level I should be spending more time with tactics and end game, however the opening is such an essential part of chess so I wanted to be somewhat familiar with the theory. I now understand that the opening position can change and therefore be labeled differently multiple times in the initial series of moves.
For example, in a Queens Gambit opening by white if black responds with a Slav Defense is the game labeled as Queen's Gambit or Slav Defense?
My question is will there be a certain point reached after a series of opening moves when one side claims the opening label. Or is there etiquette involved such as a well known black defense will always claim the opening title?
I apologize if this question seems confusing but if someone could explain how opening titles work I would appreciate it.
Thanks