Go Moku was originally played on the 19x19 Go-board, though now it is played on a 15x15 sized board (the 15x15 board became part of the standard rules in 1931 by Takagi Rakazan, the 3rd permanent meijin in 1931). In some places, the board is played on an 'infinite' array of graph paper (just tape on another sheet).

The essence of the game Go Moku is that of getting an unbroken line of five stones or marks. These may be any orientation - vertically, horizontally, or diagonally. As soon as this is done, the game is won.

Historically, the game has been around since about 700 A.D. with the introduction of Go from China into Japan. The five in a row version has gone by a number of names: Kakugo, Gomoku-narabe, Itsutsu-ishi, gobang, morphion (if anyone wishes to add translations for those, please /msg me and I will add them). Some historians believe that the game can be traced back to a five in a row game from about 100 AD called 'kakugo'. It is quite possible that many of the five in a row games have been created independent from each other - it is a relatively simple concept.

As the proficiency of players grew the simple form with no restrictions was found to be in great favor of the player who goes first. Unrestricted go moku has been solved (meaning that it has been proven that the first player can force a win given perfect play on both sides).

In 1899, to offset the first person advantage a rule was introduced to make it more difficult for black by restricting certain formations and plays on the board known as 'double three' which creates two sets of three lines with the same move:

. . . . . .
. X X . * .
. . . . X .
. . . . X .
. . . . . .
The play of the '*' above makes two sets of threes. The essence behind this is to restrict the case where the opponent can only defend himself. Playing with this move restriction is standard for family games in Japan for both players. In 1903 this rule was adopted that only black was restricted. In 1912 the rules were modified that to make such a move would mean that black looses the game - even if the play was in defense (response to another move).

A double three is only forbidden if it is not possible to stop the opponent who has nothing to attack with and is only playing defensively. If the opponent is able to stop the play it is allowed. The easiest example of this is the corner:

| . . . . .
| . . X X .
| . . * . .
| . X X . .
| . . . . .
This would be allowed because it is not necessary to block both ends of the three. Another example of this would be:
. . . . . . .
O . X X * . O
. . . . X . .
. . . . X . .
. . . . . . .
Once again, it is not possible to grow either side out fully with the horizontal row and thus it is permitted.

A further restriction placed upon black is to disallow an 'overline' from being created. An overline is a unbroken line of more than 5 marks or stones (most often six stones).

X X X * X X
Playing '*' would make an overline of 6 stones. This rule was adopted in 1916 and results in black loosing the game if such a move is played. White may make such a move without any penalty.

In 1918, a further restriction upon black was added preventing him from making what is known as a '4-3-3' which is a sequence of four stones or marks and a double three. Realize that making exactly five stones in a row is never restricted, even if it makes a double three at the same time (though there were suggestions to adopt such a rule).

The creation of a 'double four' is also prohibited for black.

At this point, one wonders how it is possible for black to win with all these restrictions (much less keep them all in the mind at once to avoid accidently shooting yourself). Realize that the '4-3' is still allowed for black:

. . . . . .
. X X * X O
. . . X . .
. . . X . .
. . . . . .
The above is a winning (and legal) move for black. The rules specify that a double three is legal if either a or b is fulfilled (or both):
  1. Not more than one of the three´s can be made to a straight four when adding another stone in just any intersection, without at the same time an overline or double-four is attained in this intersection. To find out which double-three´s, which are allowed, you must make the move, which causes the double-three, in your mind, and then continue trying to make straight fours, which are allowed, in your mind.
  2. Not more than one of the three´s can be made to a straight four when adding another stone in just any intersection, without at the same time at least two three´s meet in this intersection and make a forbidden double-three. To find out if this last double-three is forbidden or not, you must at first examine if the double-three is allowed according to a) above, and then in your mind continue trying to make straight fours of the three´s in your mind. If, when making a straight four in your mind, another double-three would be attained also these double-three´s must be examined in the same way as above.

Furthermore, there are rules regarding the legal opening moves for both players.

  • Black (first player) and white (second player) are agreed upon as tentative players.
  • Black goes first - the move must be on the center intersection.
  • Black plays the next move for white. This move must be either horizontal or vertical (called "Direct") with the first move and in direct connection with the first move. The other option for a move is diagonal to the first move and in direct connection (called "indirect").
  • Black plays the 3rd move within an empty place that is within the zone of 5x5 of the center intersection.
    After the third move, there are only 13 places for black to move in either pattern. The first player has the choice of which of the initial 26 possible board positions.
  • At this point, Black has decided where the first three moves are played. At this point, white may change sides with black if he prefers Black's position (and thus become black with all the above restrictions). Alternately, white may play the fourth move wherever he wants.
  • Black then offers his opponent two moves that he (black) will play. In a timed game, the clock counts against black until both proposals are given. The two proposals must be unequal - that is they cannot be mirror reflections of each other. Time counts against white until one of the proposals is accepted and the 6th move is made.

A win occurs when the first player completes five in a row. Six or more in a row for white is also counted as a win.

A draw occurs when all the intersections of the board are occupied, agreement between both players, both players passing in turn, or the time for both players has ended.

Complete rules may be found at http://www.renju.nu/rifrules.htm