Backgammon, a game played with draughtsmen and a special board, depending on the throw of dice. It is said to have been invented about the 10th century (Strutt). A similar game (Ludus duodecim scriptorum, the "twelve-line game") was known to the Romans, and Plato (Republic, bk. x.) alludes to a game in which dice were thrown and men were placed after due consideration. The etymology of the word "backgammon" is disputed; it is probably Saxon - baec, back, gamen, game; i.e. a game in which the players are liable to be sent back. Other derivations are, Dan. bakke, tray, gammen, game (Wedgwood); and Welsh bach, little, cammaun, battle (Henry). Chaucer alludes to a game of "tables," played with three dice, in which "men" were moved from the opponent's "tables," the game (ludus Anglicorum) being described in the Harleian MSS. (1527). The French name for backgammon is trictrac, imitative of the rattle of the dice.
Backgammon is played by two persons. The "board" (see diagram) is divided into four "tables," each table being marked with six "points" coloured differently. The inner and outer tables are separated from each other by a projecting bar. The board (in the ordinary form of the game) is furnished with fifteen white and fifteen black men, "set" or arranged as in the diagram. It is usual to make the inner table the one nearest to the light. Two dice-boxes are required, one for each player, and a pair of dice, which are used by both players. The dice are marked with numbers on their six sides, from one to six, number one being called, "ace"; two, "deuce": three, "trey." Formerly the four was called "quatre" (pronounced "cater"); the five, "cinque" (pronounced either "sank" or "sink"); and the six, "six" (size).
For the right to start each player throws one or two dice; the one who throws the higher number has the right of playing first; and he may either adopt the numbers thrown or he may throw again, using both dice.
The men are moved on from point to point, according to the throws of the dice made by the players alternately. White moves from black's inner table to black's outer, and from this to white's outer table, and so on to white's inner table; and all black's moves must be in the contrary direction. A player may move any of his men a number of points corresponding to the numbers thrown by him, provided the point to which the move would bring him is not blocked by two or more of his adversary's men being on it. The whole throw may be taken with one man, or two men maybe moved, one the exact number of points on one die, the other the number on the other die. If doublets are thrown (e.g. two sixes), four moves of that number (e.g. four moves of six points) may be made, either all by one man or separately by more. Thus, suppose white throws five, six, he may move one of his men from the left-hand corner of the black's inner table to the left-hand corner of black's outer table for six; he may, again, move the same man five points farther on, when his move is completed; or he may move any other man five points. But white cannot move a man for five from the black's ace-point, because the six-point in that table is blocked.
Any part of the throw which cannot be moved is of no effect, but it is compulsory for a player to move the whole throw unless blocked. Thus if the men were differently placed, and white could move a six, and having done so could not move a five, his move is completed. If, however, by moving the five first, he can afterwards move a six, he must make the move in that manner.
When a player so moves as to place two men on the same point, he is said to "make a point."
When there is only a single man on a point, it is called a "blot." When a blot is left, the man there may be taken up (technically the blot may be "hit") by the adversary if he throws a number which will enable him to place a man on that point. The man hit is placed on the bar, and has to begin again by entering the adversary's home table again at the next throw should it result in a number that corresponds to an unblocked point. The points in the home tables count for this purpose as 1, 2, 3, 4, 5, 6, beginning from the ace-point. A player is not allowed to move any other man while he has one to enter. It is, therefore, an advantage to have made all the points in your own board, so that your adversary, if you take a man up, cannot enter; and you can then continue throwing until a point is opened.
The game proceeds until one of the players gets all his men into his inner table or home. Then he begins to take his men off the board, or to bear them, i.e. to remove a man from any point that corresponds in number with his throw. If such a point is unoccupied, a move must be made, if there is room for it, and a move may be taken, instead of bearing a man, at any time; but when six is empty, if six is thrown a man may be borne from five and so on. If, after a player has commenced throwing off his men, he should be hit on a blot, he must enter on his adversary's inner table and must bring the man taken up into his own inner table before he can bear further.
Whoever first takes off all his men wins the game: - a single game (a "hit") if his adversary has begun bearing; a double game (a "gammon") if the adversary has not borne a man; and a triple game (a "backgammon") if, at the time the winner bears his last man, his adversary, not having borne a man, has one in the winner's inner table, or has a man up. When a series of games is played, the winner of a hit has the first throw in the succeeding game; but if a gammon is won, the players each throw a single die to determine the first move of the next game.
In order to play backgammon well, it is necessary to know all the chances on two dice and to apply them in various ways. The number of different throws that can be made is thirty-six. By taking all the combinations of these throws which include given numbers, it is easily discovered where blots may be left with the least probability of being hit. For example, to find the chance of being hit where a blot can only be taken up by an ace, the adversary may throw two aces, or ace in combination with any other number up to six, and he may throw each of these in two different ways, so that there are in all eleven ways in which an ace may be thrown. This, deducted from thirty-six (the total number of throws), leaves twenty-five; so that it is 25 to 11 against being hit on an ace. It is very important to bear in mind the chance of being hit on any number. The following table gives the odds against being hit on any number within the reach of one or two dice: -