Renju Forbidden Moves: Double-Three, Double-Four, and Overline (and Why Only Black)

The biggest difference between free-rule gomoku and Renju is the forbidden moves (kinte). In Renju, Black — the first player — has three moves it is not allowed to make: the double-three, the double-four, and the overline. These rules exist to rein in Black's first-move advantage and make the game a fair contest. Here are the three forbidden moves, why they apply to Black only, and the key exception that applies when Black makes five.

Why only Black has forbidden moves

In free-rule gomoku, the first player (Black) has an overwhelming advantage — with best play it is essentially a forced win. Renju addresses this by handicapping Black alone with forbidden moves, cancelling out the first-move edge so the game becomes balanced. That is why the forbidden moves are a Black-only rule; White, the second player, has none at all.

The three forbidden moves — double-three, double-four, overline

Black may not play any of the following; making one is an immediate loss. None of them apply to White.

• Double-three: a single move that makes two open threes (each a three with both ends free) at once. Two such threes cannot both be answered, so it is too strong — Black is forbidden from playing it.
• Double-four: a single move that makes two fours at once. Again two unstoppable threats arise together, so Black may not play it.
• Overline: Black making a line of six or more stones in a row. Black can win only with exactly five, so six-or-more is not a win but a forbidden move (a loss).

Making five takes precedence — a win beats a foul

There is an important exception: if Black's move makes exactly five in a row, it wins even if that same shape also contains a double-three or a double-four — making five takes precedence over the forbidden-move rule. An overline (six), however, is not 'five', so the exception never rescues it: an overline is always forbidden. Seen from White's side, steering Black into a position where the only finishing point is a forbidden one is a strong way to win (see the defense article). So as Black, while you chase with fours, you must check that your finishing move is not itself a forbidden move.

White has none — and the free-rule contrast

White may freely play a double-three, double-four, or overline, and for White an overline (six or more) is a win. Free-rule gomoku, by contrast, has no forbidden moves at all, and Black can win by an overline too — which is exactly why free-rule favors the first player. A simple way to remember it: 'Renju = forbidden moves for Black only; free-rule gomoku = no forbidden moves.' Play free-rule for a casual game; play Renju when you want the first and second player to be evenly matched.

How to practice

TsumeDojo's tsume Renju (VCF) problems have Black chase with fours and win with exactly five. As you read the chain of fours, get into the habit of noticing 'this point would be a double-three or double-four, so Black can't play it' — that builds the reading unique to Renju. Once you can spot forbidden moves accurately, as Black you can confirm your mate is not lost to a foul, and as White you can see how to steer Black into one.