Double Threes and Double Fours: Gomoku Winning Combinations
A gomoku double three is the most teachable winning combination: one stone makes two open threes, the opponent can answer only one. How double threes, double fours and four-threes convert, what forbidden-move rules change, and how to build the shape early.
A gomoku double three is the most teachable of all winning combinations: one stone creates two open threes at once, the opponent can answer only one, and the other turns into an open four no matter how the reply goes. Understanding it is easy. Building the shape two or three moves earlier, in a real game, is the part that takes practice. This covers how double threes, double fours and four-threes each convert into a win, which combinations forbidden-move rules take away, and a build order you can drill. The fastest way to make it stick is to try it in a live game.
Why a double three cannot be answered
An open three is one move away from an open four. An open four cannot be defended, because blocking one end leaves the other end completing five. That single property produces the whole forced line.
- Move one: place a stone that makes two open threes at once. That is the double three.
- Move two: the opponent blocks one of them and has no move left for the other.
- Move three: extend the surviving open three into an open four.
- Move four: the opponent blocks one end, you complete five from the other.
What matters is that the open four in move three is one you built, not one the opponent handed you. A double three earns its place not by looking clever but by turning a forced reply into a step of your own sequence.
Double fours and four-threes, the faster versions
A double three takes four moves to convert. Double fours and four-threes are faster, and they show up far more often in real games.
- Double four: one stone makes two straight fours with different completion points. The opponent blocks one, you complete the other on the next move.
- Four-three: one stone makes a straight four and an open three. The opponent must answer the four, then you extend the three into an open four.
- Open four: on its own it is already unstoppable and needs no support from another shape.
Ranked by speed: open four first, double four second, four-three third, double three last. Ranked by how easily you can prepare it, the order reverses, because a double three can be set up with quiet moves while double fours and four-threes usually need the opponent's stones to cooperate.
Building the shape two moves early
A double three is structure, not inspiration. Almost every one of them comes from two existing open twos whose extension lines cross.
- Place an open two in two different directions so that their extension lines intersect.
- The intersection must be empty, and a stone there must complete a continuous three in both directions.
- Prefer a diagonal paired with a straight line, since diagonals are what players miss when scanning.
- Check that the point is not one your opponent can answer with a straight four, or you will be forced to defend first.
Here is a self-check you can run immediately: list every open two you have on the board, extend their lines, and look at where two lines meet. Those intersections are your double-three candidates. Most players never find them because they never count their own open twos.
Under forbidden-move rules
Formal Renju rules restrict black to offset the first-move advantage. A move that creates two open threes at once is forbidden for black and loses on the spot. So does a double four. So does an overline of six or more.
- Double three: black making two open threes with one stone loses.
- Double four: black making two fours with one stone loses.
- Overline: six or more in a row does not count as a win for black.
- White has none of these restrictions and may use double threes and double fours freely.
One detail gets missed often: a four-three is not forbidden. Black creating a straight four plus an open three with one move is legal, and it is black's main way to win under forbidden-move rules. Confirm which ruleset you are playing on the gomoku rules page.
How white uses the double three
White carries no forbidden moves, which makes the double three the most reliable way for the second player to turn a game around. The best moment to build one is while black is committed to attacking one side.
- While black builds threats on the left, settle two quiet open twos on the right.
- Keep your open twos off black's extension lines so they are not blocked as a side effect.
- Do not delay once the intersection exists. If black occupies it, the chance does not come back.
White also has a quieter weapon: forcing black onto a forbidden point. When black has to block at a square that would also create a double three, black cannot play there at all. That is part of what compensates the second player, and the defense guide covers it in more detail.
Spotting the opponent's double three
- Count the opponent's open twos. Two of them means a threat exists.
- Extend their lines and find the crossing point. If it is empty, that square is the threat.
- If that square also gives the opponent a straight four, block the square rather than the existing shape.
The third line is the one that matters. Blocking the shape only delays the threat; blocking the intersection removes it. Most players start defending after the double three already exists, which is too late. The correct moment is the move right after the opponent's second open two lands.
Does a double three always win?
It wins as long as the opponent has no stronger threat. If they are holding a straight four, they complete five before you reach move three, so always clear the opponent's fours first.
Is a double three a forbidden move for black?
Under Renju forbidden-move rules, yes, and it loses immediately. Under freestyle rules it is not, and black may use it freely. Check the ruleset before you start.
Which is more practical, a double three or a four-three?
The four-three. It needs only a straight four plus an open three, so it is easier to construct, converts faster, and stays legal for black.
How do I train the eye for finding them?
Review each game afterwards and count the moments when two open twos coexisted and nobody used them. In play, use a time limit so you scan intersections every move. Speed comes from repetition, not from long thinking.
All three combinations, the forbidden-move boundaries, and the habit of looking for intersections can only be trained in real games. Open a live game with no sign-up; the AI running in your browser keeps producing shapes worth judging. Basic moves are on the how to play page.