Answers.Body: <p>Openings are typically decided by <a href="https://www.365chess.com/eco.php" rel="noreferrer">ECO Codes</a>.</p>
  
  <p>So as few as one move and as many as 5-6 or more moves could decide an opening. For example, as soon as you play 1. b3 it is a Nimzo-Larsen attack. (A01)</p>
  
  <p>As soon as 1. e4 c5 is played it is a Sicilian defence. (B20) But there are many variations. If the game continues 2. Nf3 e6 3. d4 cxd4 4. Nxd4 a6, it becomes the Kan variation. (B41) So on and so forth. You can find a full list of recognized openings and their ECO codes in the link above.</p>
  
  <p>As for your second question, no, after the identifying moves have been played, the opening is typically not completed yet. For example, take this line of the Budapest gambit.</p>
  
  <pre><code>[FEN ""]
  [Event "Budapest Gambit"]
  
  1. d4 Nf6 2. c4 e5 3. dxe5 Ng4 4. Nf3
  </code></pre>
  
  <p>This is as many moves as it takes to recognize the opening as Budapest Gambit, Adler Variation (A52). However, you can hardly say the opening is over.</p>
  
  <pre><code>[FEN ""]
  [Event "Budapest Gambit"]
  
  1. d4 Nf6 2. c4 e5 3. dxe5 Ng4 4. Nf3 Nc6 5. Bf4 Bb4+ 6. Nc3 Bxc3 7. bxc3 Qe7 8. Qd5 f6 (8... Qa3)
  </code></pre>
  
  <p>This is a very common continuation to the Budapest Gambit, even though these moves aren't needed to identify it as such - it is all still theory. The player isn't "on his own", there are still many established lines to follow.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-04-04T10:43:38.650Z
Answers.Text: ECO codes are a bit technical, and the opinion of a single publisher. There are many variations that get names in there because ECO needed a name for them, that aren't really recognized by any chess players. Like the "Adler variation", I've never seen that used in any article about some line in 4.Nf3.
Answers.UserDisplayName: RemcoGerlich
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Answers.Text: @RemcoGerlich True. Re this example, I'm not particularly sure why ECO distinguishes between 4. Nf3 and 4. Bf4, since the one not played is typically the 5th move anyway.
Answers.UserDisplayName: Quintec
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Answers.Text: There are differences, after 4.Nf3 black can play 4...Bc5 forcing 5.e3, and the bishop is locked in. And after 4.Bf4 he can play 4...g5!? making the position sharper.
Answers.UserDisplayName: RemcoGerlich
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Answers.UserDisplayName: Quintec
Answers.Body: <blockquote>
    <p>How many opening moves are needed before we can identify that such moves fall into a particular well-known opening such as Ruy Lopez, London, kings gambit, an so on?</p>
  </blockquote>
  
  <p>It depends on the opening. Some are more strictly defined than others; e.g. a game is really only a "Ruy Lopez" if it reached the position after 1.e4 e5 2.Nf3 Nc6 3.Bb5, but lots of different lines where white plays an early d2-d4 and black's ...c7-c5 is answered by d4-d5 are called "Benoni".</p>
  
  <p>Some variations have a well-known name on move 12-ish (like the Soltis variation in the Dragon), whereas a major line used in world championship matches like 1.Nf3 d5 2.g3 g6 doesn't even have a real name at all.</p>
  
  <p>There's really no logic to it, it's a bunch a historical accidents and traditions.</p>
  
  <p>But these are only the <strong>names</strong> of openings. They are useful when talking to somebody about your game, or when you need a title for your new book or you are looking for a book, and for nothing else.</p>
  
  <p>They are completely unrelated to how much a given player knows about some opening. Especially opening books often start <em>from</em> some named position.</p>
  
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Answers.LastEditDate: 2020-04-04T10:44:23.837Z
Answers.UserDisplayName: RemcoGerlich
Answers.Body: <p><a href="https://en.wikipedia.org/wiki/List_of_chess_openings" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/List_of_chess_openings</a> has what you want.</p>
  
  <blockquote>
    <p>And after such identifying moves, can we we say that such opening is already completed and the player is on his own for the development of his pieces</p>
  </blockquote>
  
  <p>Openings certainly don't "complete" like that. In fact, ECO openings only give you the head start. Whether a player is on his own depends on the skills. For example, grandmasters certainly understands better chess than the wikipedia can give.</p>
  
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Answers.UserDisplayName: SmallChess
Body: <p>How many opening moves are needed before we can identify that such moves fall into a particular well-known opening such as  Ruy Lopez, London, kings gambit, an so on? And after such identifying moves, can we we say that such opening is already completed and the player is on his own for the development of his pieces?</p>
  
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-04-05T22:27:32.023Z
Comments.Text: You may be interested in this related question: [Which opening requires the longest amount of chess moves?](https://chess.stackexchange.com/questions/24608/which-opening-requires-the-longest-amount-of-chess-moves/24610)
Comments.UserDisplayName: itub
Tags: <opening><learning>
Title: How do we identify opening lines?
ThreadText: # How do we identify opening lines?
  
  (Asked by: username_0 on 2020-04-03)
  
  How many opening moves are needed before we can identify that such moves fall into a particular well-known opening such as Ruy Lopez, London, kings gambit, an so on? And after such identifying moves, can we we say that such opening is already completed and the player is on his own for the development of his pieces?
  
  **Tags:** opening, learning
  
  > **Comments:**
  > **username_1**: You may be interested in this related question: [Which opening requires the longest amount of chess moves?](https://chess.stackexchange.com/questions/24608/which-opening-requires-the-longest-amount-of-chess-moves/24610)  
  
  ---
  
  ## 3 answers
  
  ### Answer by username_2 on 2020-04-03. Score: 5
  
  Openings are typically decided by [ECO Codes](https://www.365chess.com/eco.php).
  
  So as few as one move and as many as 5-6 or more moves could decide an opening. For example, as soon as you play 1. b3 it is a Nimzo-Larsen attack. (A01)
  
  As soon as 1. e4 c5 is played it is a Sicilian defence. (B20) But there are many variations. If the game continues 2. Nf3 e6 3. d4 cxd4 4. Nxd4 a6, it becomes the Kan variation. (B41) So on and so forth. You can find a full list of recognized openings and their ECO codes in the link above.
  
  As for your second question, no, after the identifying moves have been played, the opening is typically not completed yet. For example, take this line of the Budapest gambit.
  
  ```
  [FEN ""]
  [Event "Budapest Gambit"]
  
  1. d4 Nf6 2. c4 e5 3. dxe5 Ng4 4. Nf3
  
  ```
  
  This is as many moves as it takes to recognize the opening as Budapest Gambit, Adler Variation (A52). However, you can hardly say the opening is over.
  
  ```
  [FEN ""]
  [Event "Budapest Gambit"]
  
  1. d4 Nf6 2. c4 e5 3. dxe5 Ng4 4. Nf3 Nc6 5. Bf4 Bb4+ 6. Nc3 Bxc3 7. bxc3 Qe7 8. Qd5 f6 (8... Qa3)
  
  ```
  
  This is a very common continuation to the Budapest Gambit, even though these moves aren't needed to identify it as such - it is all still theory. The player isn't "on his own", there are still many established lines to follow.
  
  > **Comments:**
  > **username_3**: ECO codes are a bit technical, and the opinion of a single publisher. There are many variations that get names in there because ECO needed a name for them, that aren't really recognized by any chess players. Like the "Adler variation", I've never seen that used in any article about some line in 4.Nf3.  
  > **username_2**: @username_3 True. Re this example, I'm not particularly sure why ECO distinguishes between 4. Nf3 and 4. Bf4, since the one not played is typically the 5th move anyway.  
  > **username_3**: There are differences, after 4.Nf3 black can play 4...Bc5 forcing 5.e3, and the bishop is locked in. And after 4.Bf4 he can play 4...g5!? making the position sharper.  
  
  ---
  
  ### Answer by username_3 on 2020-04-04. Score: 3
  
  > How many opening moves are needed before we can identify that such moves fall into a particular well-known opening such as Ruy Lopez, London, kings gambit, an so on?
  
  It depends on the opening. Some are more strictly defined than others; e.g. a game is really only a "Ruy Lopez" if it reached the position after 1.e4 e5 2.Nf3 Nc6 3.Bb5, but lots of different lines where white plays an early d2-d4 and black's ...c7-c5 is answered by d4-d5 are called "Benoni".
  
  Some variations have a well-known name on move 12-ish (like the Soltis variation in the Dragon), whereas a major line used in world championship matches like 1.Nf3 d5 2.g3 g6 doesn't even have a real name at all.
  
  There's really no logic to it, it's a bunch a historical accidents and traditions.
  
  But these are only the **names** of openings. They are useful when talking to somebody about your game, or when you need a title for your new book or you are looking for a book, and for nothing else.
  
  They are completely unrelated to how much a given player knows about some opening. Especially opening books often start *from* some named position.
  
  
  ---
  
  ### Answer by username_4 on 2020-04-03. Score: 2
  
  <https://en.wikipedia.org/wiki/List_of_chess_openings> has what you want.
  
  > And after such identifying moves, can we we say that such opening is already completed and the player is on his own for the development of his pieces
  
  Openings certainly don't "complete" like that. In fact, ECO openings only give you the head start. Whether a player is on his own depends on the skills. For example, grandmasters certainly understands better chess than the wikipedia can give.
  
  
  ---
  
  