Checkers (American English and Canadian English), also called American Checkers, Straight Checkers or, English Draughts (British English), is a popular board game all over the world. Unlike International Checkers, it is played on an eight-by-eight squared board (with sixty-four total squares) with twelve pieces on each side. The pieces move and capture diagonally. They may only move forward until they reach the opposite end of the board, when they are crowned or kinged and may henceforth move and capture both backward and forward.
As in all checkers variants, American Checkers is played by two people, on opposite sides of a playing board, alternating moves. Traditionally the pieces are either black, red, or white. The opponent's pieces are captured by jumping over them.
Over-the-board tournaments are (or were) held in Australia, Barbados, Canada, Channel Islands, China, Denmark, Germany, Guyana, Ireland, Italy, Kenya, New Zealand, South Africa, Turkmenistan, the United Kingdom and the United States.
- Pieces – Though pieces were traditionally made of wood, now many are made of plastic, though other materials may be used. Pieces are typically flat and cylindrical. They are invariably split into one darker and one lighter colour. Traditionally, these colours are white and red, but black and red are common in the United States, and light- and dark-stained wooden pieces are supplied with more expensive sets. There are two classes of pieces: men and kings. Kings are differentiated as consisting of two normal pieces of the same colour, stacked one on top of the other. Often indentations are added to the pieces to aid stacking.
- Starting position – Each player starts with twelve pieces on the dark spaces of the three rows closest to that person's own side (as shown in the diagram). The row closest to each player is called the crownhead or kings row. The player with the darker coloured pieces moves first.
- How to move – There are two ways to move a piece:
- A simple move involves sliding a piece one space diagonally forwards to an adjacent unoccupied dark square.
- A jump is a move from a square diagonally adjacent to one of the opponent's pieces to an empty square immediately and directly on the opposite side of the opponent's square, thus jumping directly over the square containing the opponent's piece. An uncrowned piece may only jump diagonally forwards, kings may also jump diagonally backwards. A piece that is jumped is captured and removed from the board. Multiple-jump moves are possible if when the jumping piece lands, there is another immediate piece that can be jumped; even if the jump is in a different direction. Jumping is mandatory – whenever a player has the option to jump, that person must jump (even if it's to the jumping player's disadvantage; for example, a player can choose to allow one of his men to get captured to set up capturing two or more of his/her opponent's men). When multiple-option jumping moves are available, whether with the one piece in different directions or multiple pieces that can make various jumping moves, the player may choose which piece to jump with and which jumping option or sequence of jumps to make. The jumping sequence chosen does not necessarily have to be the one that would have resulted in the most captures; however, one must make all available captures in the chosen sequence. Any piece, whether it is a king or not, can jump a king.
- Kings – If a player's piece moves into the kings row on the opposing player's side of the board, that piece is said to be crowned (or often kinged in the U.S.), becoming a king and gaining the ability to move both forwards and backwards. If a player's piece jumps into the kings row, the current move terminates; having just been crowned, the piece cannot continue on by jumping back out (as in a multiple jump), until the next move. A piece is normally crowned by placing a second piece on top of it; some sets have pieces with a crown molded, engraved or painted on one side, allowing the player to simply turn the piece over or to place the crown-side up on the crowned piece, further differentiating Kings from ordinary pieces.
- How the game ends – A player wins by capturing all of the opposing player's pieces or by leaving the opposing player with no legal moves. The game ends in a draw, if neither side can force a win.
In Tournament Checkers, a variation called three-move restriction is preferred. The first three moves are drawn at random from a set of accepted openings. Two games are played with the chosen opening, each player having a turn at either side. This tends to reduce the number of draws and can make for more exciting matches. Three-move restriction has been played in the United States championship since 1934. A two-move restriction was used from 1900 until 1934 in the United States and in the British Isles until the 1950s. Before 1900, championships were played without restriction: this style is called go-as-you-please (GAYP).
One rule of long standing that has fallen out of favour is the huffing rule. In this variation jumping is not mandatory, but if a player does not take their jump (either deliberately or by failing to see it), the piece that could have made the jump is blown or huffed, i.e. removed from the board. After huffing the offending piece, the opponent then takes their turn as normal. Huffing has been abolished by both the American Checker Federation and the English Draughts Association.
Two common rule variants, not recognized by player associations, are:
- That capturing with a king precedes capturing with a regular piece. (In such a case, any available capture can be made at the player's choice.)
- A piece which in the current move has become a king can then in the same move go on to capture other pieces (see under Kings, above).
- Main article: Portable Draughts Notation
For recording games, there is a standardised notation. All 32 reachable positions of the board are numbered in sequence. The numbering starts in black's double-corner. The blacks squares on the first rank are numbered 1 to 4, (in algebraic chess notation those being g1, e1, c1, a1. The next rank starts 5 to 8 (h2, f2, d2, b2) and so on. Moves are recorded as from-to, so a move from 9 to 14 would be 9-14. Captures are notated with an x connecting the start and end square. The result is often abbreviated as BW/RW (Black/Red wins) or WW (White wins)
A sample game. White resigned after blacks 46th move.
[Event "1981 World Championship Match, Game #37"]
[Black "M. Tinsley"]
[White "A. Long"]
1. 9-14 23-18 2. 14x23 27x18 3. 5-9 26-23 4. 12-16 30-26 5. 16-19 24x15 6. 10x19 23x16 7. 11x20 22-17 8. 7-11 18-15 9. 11x18 28-24 10. 20x27 32x5 11. 8-11 26-23 12. 4-8 25-22 13. 11-15 17-13 14. 8-11 21-17 15. 11-16 23-18 16. 15-19 17-14 17. 19-24 14-10 18. 6x15 18x11 19. 24-28 22-17 20. 28-32 17-14 21. 32-28 31-27 22. 16-19 27-24 23. 19-23 24-20 24. 23-26 29-25 25. 26-30 25-21 26. 30-26 14-9 27. 26-23 20-16 28. 23-18 16-12 29. 18-14 11-8 30. 28-24 8-4 31. 24-19 4-8 32. 19-16 9-6 33. 1x10 5-1 34. 10-15 1-6 35. 2x9 13x6 36. 16-11 8-4 37. 15-18 6-1 38. 18-22 1-6 39. 22-26 6-1 40. 26-30 1-6 41. 30-26 6-1 42. 26-22 1-6 43. 22-18 6-1 44. 14-9 1-5 45. 9-6 21-17 46. 18-22 BW
In Unicode, the checkers are encoded in block Miscellaneous Symbols:
- U+26C0 WHITE CHECKERS MAN
- U+26C1 WHITE CHECKERS KING
- U+26C2 BLACK CHECKERS MEN
- U+26C3 BLACK CHECKERS KING
The first English draughts computer program was written by Christopher Strachey, M.A. at the National Physical Laboratory, London. Strachey finished the programme, written in his spare time, in February 1951. It ran for the first time on NPL's Pilot ACE on 30 July 1951. He soon modified the programme to run on the Manchester Mark 1.
The second computer program was written in 1956 by Arthur Samuel, a researcher from IBM. Other than it being one of the most complicated game playing program written at the time, it is also well known for being one of the first adaptive program. It learned by playing games against modified versions of itself, with the victorious versions surviving. Samuel's program was far from mastering the game, although one win against a blind checkers master gave the general public the impression that it was very good.
In the 1990s, the strongest program was Chinook, written in 1989 by a team from the University of Alberta led by Jonathan Schaeffer. Marion Tinsley, world champion from 1955–62 and from 1975–91, won a match against the machine in 1992. In 1994, Tinsley had to resign in the middle of an even match for health reasons; he died shortly thereafter. In 1995, Chinook defended its man-machine title against Don Lafferty in a thirty-two game match. The final score was 1–0 with 31 draws for Chinook over Don Lafferty. In 1996 Chinook won in the USA National Tournament by the widest margin ever, and was retired from play after that event. The man-machine title has not been contested since.
In July 2007, in an article published in Science magazine, Chinook's developers announced that the program had been improved to the point where it could not lose a game. If no mistakes were made by either player, the game would always end in a draw. After eighteen years, they have computationally proven a weak solution to the game of Checkers. Using between two hundred desktop computers at the peak of the project and around fifty later on, the team made just 1014 calculations to search from the initial position to a database of positions with at most ten pieces.
The number of legal positions in American Checkers is estimated to be 1020, and it has a game-tree complexity of approximately 1040. By comparison, Chess is estimated to have between 1043 and 1050 legal positions.
When draughts is generalized so that it can be played on an n-by-n board, the problem of determining if the first player has a win in a given position is EXPTIME-complete.
The July 2007 announcement by Chinook's team stating that the game had been solved must be understood in the sense that, with perfect play on both sides, the game will always finish with a draw. Yet, not all positions that could result from imperfect play have been analyzed.
List of Top Checkers Programs
- Minicheckers, a variant played on a 4x4 board
- Suicide Checkers, the misère variant
- Tiers, a complex variant of Checkers that allows players to upgrade their pieces beyond kings
- World Draughts Federation
- English Draughts Association
- American Checkers Federation
- List of World Checkers Champions