A thread for discussing the opening phase of chess games.
- There is no agreed on definition for "opening phase". See #3.
- The Oxford Companion to Chess lists 1,327 named openings and variants.
- The Encyclopaedia of Chess Openings (ECO) code categorizes the chess openings into five broad areas ("A" through "E"), with each of those broken down into one hundred subcategories ("00" through "99"). Therefore, 500 top level categories.
- The longest number of moves in an ECO opening that has a name is the Ruy López Opening: Marshall Attack, Modern, Main Line, Spassky Variation. It is 18 moves for both sides.
1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.O-O Be7 6.Re1 b5 7.Bb3 O-O 8.c3 d5 9.exd5 Nxd5 10.Nxe5 Nxe5 11.Rxe5 c6 12.d4 Bd6 13.Re1 Qh4 14.g3 Qh3 15.Be3 Bg4 16.Qd3 Rae8 17.Nd2 Re6 18.a4 Qh5
- The number of possible games per plies (half-moves) made according to
en.wikipedia.org/wiki/Shannon_number
Number of plies Number of possible games
1 20
2 400
3 8,902
4 197,281
5 4,865,609
6 119,060,324
7 3,195,901,860
8 84,998,978,956
9 2,439,530,234,167
10 69,352,859,712,417
- From that same page:
Shannon showed a calculation for the lower bound of the game-tree complexity of chess, resulting in about 10^120 possible games.
As a comparison, the number of atoms in the observable universe, to which it is often compared, is roughly estimated to be 10^80.
The number of "sensible" games that can be played (not counting ridiculous or obvious game-losing moves such as moving a queen to be immediately captured by a pawn without compensation), then the result is closer to around 10^40 games. This is based on having a choice of about three sensible moves at each ply (half a move), and a game length of 80 ply (40 moves)
- But many of these games would reach the same position with the same player to move and possible moves per the rules (en passant, castling, etc). So in some sense the space is not as big as these numbers. It is still impractical to solve chess this way. The point Shannon was making was the impracticality of solving chess by brute force.
For comparison, 4×4×4 tic-tac-toe was solved by Oren Patashnik in 1980 by brute force (the first player can force a win).
Also for comparison, the game of Hex on an 11x11 board has a tree size of 10^98. John Nash was the first to prove (c. 1949) that Hex is a win for the first player. However, the winning method is unknown! The proof Nash used was to show that the second player could not have a winning method. He did that by what is known as a "strategy stealing" argument. Since Nash also proved that Hex cannot end in a draw, the only conclusion left is that the first player has a win.
- The Oxford Companion to Chess lists 1,327 named openings and variants.
- The Encyclopaedia of Chess Openings (ECO) code categorizes the chess openings into five broad areas ("A" through "E"), with each of those broken down into one hundred subcategories ("00" through "99"). Therefore, 500 top level categories.
- The longest number of moves in an ECO opening that has a name is the Ruy López Opening: Marshall Attack, Modern, Main Line, Spassky Variation. It is 18 moves for both sides.
1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.O-O Be7 6.Re1 b5 7.Bb3 O-O 8.c3 d5 9.exd5 Nxd5 10.Nxe5 Nxe5 11.Rxe5 c6 12.d4 Bd6 13.Re1 Qh4 14.g3 Qh3 15.Be3 Bg4 16.Qd3 Rae8 17.Nd2 Re6 18.a4 Qh5
- The number of possible games per plies (half-moves) made according to
en.wikipedia.org/wiki/Shannon_number
Number of plies Number of possible games
1 20
2 400
3 8,902
4 197,281
5 4,865,609
6 119,060,324
7 3,195,901,860
8 84,998,978,956
9 2,439,530,234,167
10 69,352,859,712,417
- From that same page:
Shannon showed a calculation for the lower bound of the game-tree complexity of chess, resulting in about 10^120 possible games.
As a comparison, the number of atoms in the observable universe, to which it is often compared, is roughly estimated to be 10^80.
The number of "sensible" games that can be played (not counting ridiculous or obvious game-losing moves such as moving a queen to be immediately captured by a pawn without compensation), then the result is closer to around 10^40 games. This is based on having a choice of about three sensible moves at each ply (half a move), and a game length of 80 ply (40 moves)
- But many of these games would reach the same position with the same player to move and possible moves per the rules (en passant, castling, etc). So in some sense the space is not as big as these numbers. It is still impractical to solve chess this way. The point Shannon was making was the impracticality of solving chess by brute force.
For comparison, 4×4×4 tic-tac-toe was solved by Oren Patashnik in 1980 by brute force (the first player can force a win).
Also for comparison, the game of Hex on an 11x11 board has a tree size of 10^98. John Nash was the first to prove (c. 1949) that Hex is a win for the first player. However, the winning method is unknown! The proof Nash used was to show that the second player could not have a winning method. He did that by what is known as a "strategy stealing" argument. Since Nash also proved that Hex cannot end in a draw, the only conclusion left is that the first player has a win.
- Since there is no agreed on definition of opening phase (or of opening) let's look at an attempt.
From en.wikipedia.org/wiki/Chess_opening
"A chess opening or simply an opening refers to the initial moves of a chess game. The term can refer to the initial moves by either side, White or Black, but an opening by Black may also be known as a defense."
The usual number of moves people consider belong to the "initial moves" are the first 10 to 15. The expectation is that by that time both sides will have had enough moves to develop all their pieces. 8 men to develop and allowing for one move each of those and 2 pawn moves would give 10. (The King "develops" when it castles, but I've allowed for moving that castled Rook again.) Obviously there are going to be exceptions; many exceptions.
After the opening, people say that the "middle game" begins. That's right, the definition of middle game depends on the definition of opening phase.
While we are looking at definitions of the phases of the game we may as well consider the "endgame". Again there is no agreed on definition. Here is one I've seen: "The stage of the game when there are few pieces left on the board." How few is few? Some endgame specialist say as soon as there are no Queens on the board. Another definition is that the endgame starts when the King can become active. Now you'd have to define what an "active King" means.
To all of these definitions, exceptions are the rule.
From en.wikipedia.org/wiki/Chess_opening
"A chess opening or simply an opening refers to the initial moves of a chess game. The term can refer to the initial moves by either side, White or Black, but an opening by Black may also be known as a defense."
The usual number of moves people consider belong to the "initial moves" are the first 10 to 15. The expectation is that by that time both sides will have had enough moves to develop all their pieces. 8 men to develop and allowing for one move each of those and 2 pawn moves would give 10. (The King "develops" when it castles, but I've allowed for moving that castled Rook again.) Obviously there are going to be exceptions; many exceptions.
After the opening, people say that the "middle game" begins. That's right, the definition of middle game depends on the definition of opening phase.
While we are looking at definitions of the phases of the game we may as well consider the "endgame". Again there is no agreed on definition. Here is one I've seen: "The stage of the game when there are few pieces left on the board." How few is few? Some endgame specialist say as soon as there are no Queens on the board. Another definition is that the endgame starts when the King can become active. Now you'd have to define what an "active King" means.
To all of these definitions, exceptions are the rule.
Opening Survey: A warning first.
An often asked question is how to go about surveying the possible openings. People usually ask this because they want some guidance on creating an opening repertoire.
Before answering this, I want to point out that almost all teachers recommend that beginners do not play the opening by rote! It is much better to start with rules-of-thumb (ROT) for the opening, and an understanding of some major exceptions to those ROT. Then beginners should spend their study time on deliberate practice of tactics and elementary endgames.
When the beginner is ready to go beyond the ROT, Silman's recommendation is to play an opening system. He recommends in his video series with the Great Courses that you play the Colle-Zukertort.system as White. As Black, Silman recommends the Queen's Gambit Declined Tartakower Variation against 1.d4 and the French Defense against 1.e4. You still do not play these openings by rote. You have to learn the plans that are possible by both sides, where to best place your pieces, etc. If you do not do this and instead just memorize moves, then as soon as you are at the end of the variation you've memorized you will have much difficulty finding candidate moves because you really do not understand the position in any way that helps.
By the way, the phrase "opening system" is also not well defined. However, the intent of the idea is that one pays more attention to the placement of your pawns and pieces than in the specific moves. Obviously you have to pay attention to what your opponent is doing, so this idea does not mean that you blindly play your moves.
An often asked question is how to go about surveying the possible openings. People usually ask this because they want some guidance on creating an opening repertoire.
Before answering this, I want to point out that almost all teachers recommend that beginners do not play the opening by rote! It is much better to start with rules-of-thumb (ROT) for the opening, and an understanding of some major exceptions to those ROT. Then beginners should spend their study time on deliberate practice of tactics and elementary endgames.
When the beginner is ready to go beyond the ROT, Silman's recommendation is to play an opening system. He recommends in his video series with the Great Courses that you play the Colle-Zukertort.system as White. As Black, Silman recommends the Queen's Gambit Declined Tartakower Variation against 1.d4 and the French Defense against 1.e4. You still do not play these openings by rote. You have to learn the plans that are possible by both sides, where to best place your pieces, etc. If you do not do this and instead just memorize moves, then as soon as you are at the end of the variation you've memorized you will have much difficulty finding candidate moves because you really do not understand the position in any way that helps.
By the way, the phrase "opening system" is also not well defined. However, the intent of the idea is that one pays more attention to the placement of your pawns and pieces than in the specific moves. Obviously you have to pay attention to what your opponent is doing, so this idea does not mean that you blindly play your moves.
Opening Survey
Once you are ready to do a survey of the openings there are several ways to do it. You can also combine these.
- Pick a book that has such a survey.
One such book that covers 44 openings is Silman's "The Complete Book of Chess Strategy". Silman describes, mostly in words instead of variations, what these openings plans are. There is very little said about where the names of the openings come from or the history of the openings. This book is more than a survey of the openings. The first part is about the openings, then comes a part on the middle game, a part on the endgame, and a part on practical matters. The parts are organized alphabetically by chess terms.
Another book, entirely on openings and including much more on the history, is "Fundamental Chess Openings" by Paul van der Sterren.
- Use wikipedia.
The page en.wikipedia.org/wiki/Chess_opening is itself a survey. On that page are many links when one is ready to pursue some opening deeper. Those links will include much more information including history.
- Ask your mentor.
If you have a chess mentor, I recommended in the Beginner Course to get one, then your mentor can go over some of your games and work with your objectives to point out which openings you might want to look at.
Once you are ready to do a survey of the openings there are several ways to do it. You can also combine these.
- Pick a book that has such a survey.
One such book that covers 44 openings is Silman's "The Complete Book of Chess Strategy". Silman describes, mostly in words instead of variations, what these openings plans are. There is very little said about where the names of the openings come from or the history of the openings. This book is more than a survey of the openings. The first part is about the openings, then comes a part on the middle game, a part on the endgame, and a part on practical matters. The parts are organized alphabetically by chess terms.
Another book, entirely on openings and including much more on the history, is "Fundamental Chess Openings" by Paul van der Sterren.
- Use wikipedia.
The page en.wikipedia.org/wiki/Chess_opening is itself a survey. On that page are many links when one is ready to pursue some opening deeper. Those links will include much more information including history.
- Ask your mentor.
If you have a chess mentor, I recommended in the Beginner Course to get one, then your mentor can go over some of your games and work with your objectives to point out which openings you might want to look at.
Working on Colle opening.
See lichess.org/study/6P90HTwf
See lichess.org/study/6P90HTwf
I recently added links to the Opening chapter in the Advanced Course:
I wonder if there is any tool that can be used to recognize reversed openings.
It is easy enough to take someone out of book. For example, sacrifice a pawn for easy development.
[Give examples.]
[Give examples.]
Playing an opening system and not carefully watching what your opponent is doing is a "bad idea". See game 23 in LCMBM.
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