What is Gravity Tic-Tac-Toe?
Gravity Tic-Tac-Toe plays as if the board stood upright. Instead of choosing a square, you choose a column, and your mark drops to the lowest empty square in it. A full column takes no more marks. Everything else is standard: X moves first, three of your marks in a row across, down or diagonally wins, and a full board without a line is a draw.
Gravity takes away most of the choice. On the 3×3 board there are at most three moves each turn, and a square becomes playable only once the square below it is filled. That makes threats a matter of timing: a line you can finish only on a square that is not reachable yet is useless until someone fills the square beneath it, and neither player wants to be the one who does.
On the 3×3 board the game is still a draw with perfect play, as a computer search of every position confirms. Gravity also works on the 4×4 and 5×5 boards, where four in a row wins, and combines with Misère and Wild.
Rule changes
| Rule | Standard Tic-Tac-Toe | Gravity Tic-Tac-Toe |
|---|---|---|
| Where you play | Standard Tic-Tac-ToeAny empty square. | Gravity Tic-Tac-ToeChoose a column; your mark drops to the lowest empty square in it. A full column is closed. |
| How to win | Standard Tic-Tac-ToeComplete a line of three of your marks, or four on the 4×4 and 5×5 boards. | Gravity Tic-Tac-ToeThe same, across, down or diagonally. |
| Perfect play | Standard Tic-Tac-ToeA draw. | Gravity Tic-Tac-ToeStill a draw on the 3×3 board. |
| Board and options | Standard Tic-Tac-ToeA 3×3 board. The table setup also offers 4×4 and 5×5 boards. | Gravity Tic-Tac-ToeAny board size. Gravity combines with Misère, which on 3×3 becomes a win for the first player, and with Wild. |
History
There is no standard rule book for gravity tic-tac-toe: it is the drop rule of Four in a Row applied to the tic-tac-toe board, and the rules here are this site's own. That rule became widely known through the upright four-in-a-row game designed by Howard Wexler and first sold in February 1974. It is played on an upright grid of six rows and seven columns, in which each disc falls to the lowest open slot of the column it is dropped into.
Four in a Row is also on this site, if you want the drop rule on the larger grid with four in a row to win.