If you learn only one attacking pattern in gomoku, make it the four-three. It decides a huge share of practical games, in freestyle and in Vietnamese caro alike, and once you understand how it works you will start seeing it — for yourself and for your opponent — in almost every game.
What a four-three is
A four-three is a single move that creates two threats at once:
- a four (four marks with one way to make five), and
- an open three (three marks that can become an open four next move).
The defender is in an impossible position. The four must be blocked immediately, or the attacker makes five. But blocking the four uses the defender's move, and the attacker then turns the open three into an open four — which cannot be stopped.
Let us walk through the diagram:
- X plays i8. Row 8 now reads f8–g8–h8–i8, blocked on the left by O's e8. It threatens five at j8. Column i now reads i6–i7–i8, with empty points at i5 and i9 (and further at i4 and i10): an open three.
- O must play j8, or X makes five there.
- X plays i9 (or i5), making i6–i9 (or i5–i8), four in a row with both ends empty: an open four.
- O blocks one end; X completes five at the other.
Under blocked-ends rules the combination still works: the final five on column i has one open end, so it is not blocked at both ends.
Why it is so reliable
A four-three is forcing. The four leaves the defender exactly one legal reply that does not lose at once. That means the attacker can calculate the whole sequence with certainty — there are no surprises, no alternatives to consider. Compare this with a double three, where the defender has more freedom (see double-three attack).
The only escape for the defender is if their forced block happens to create a four of their own, or if they already have fours available that they can make first to regain the initiative. That is why, before playing a four-three, you should always check: does the opponent have any four they can make in reply?
How four-threes are built
Four-threes do not appear from nowhere. They come from two of your lines — one with three marks and one with two — crossing at an empty point. In the diagram, row 8 had three X marks and column i had two, and they crossed at i8.
To build four-threes, then:
- Collect lines in different directions near each other. Isolated lines never cross.
- Look for crossing points — empty points where two of your lines meet. Mentally mark them.
- Make one line a three and the other a two, with the crossing point still empty. Now the four-three is one move away.
The defender's job is to occupy your crossing points before you use them, so good attackers often build several crossings at once, knowing the defender can only take one per move.
Getting there with forcing moves
Often the crossing is not ready yet — you need one more mark on one of the lines. Instead of a quiet move (which gives the defender time to occupy the crossing), strong players use a forcing move to add that mark: a four whose forced reply is harmless, or an open three the defender must block.
The idea: every forcing move places one of your marks while the defender's reply goes to a predictable point. If your forcing marks land on the lines that meet at the crossing, you arrive at the four-three before the defender can stop it. This technique is covered in victory by continuous fours.
Spotting a four-three coming
As a defender, you can often see a four-three one or two moves ahead. Look for:
- A crossing point where the opponent has three on one line and two on another.
- A crossing point where the opponent has two and two — one quiet move away from a three-two, and then a four-three.
- A closed three and an open two pointing at the same empty point.
When you find such a point, occupying it is usually the best defence — better than blocking either line separately. If the point also helps your own shape, even better.
Common mistakes
Attacking without checking the opponent's fours. Your four must be blocked — but if the defender's forced block also creates a four for them, you have to answer it, and that lost tempo may let them block your open three as well. Check their potential fours before you start.
Making the four at the wrong end. Sometimes the three-plus-two crossing allows the four-three in two ways, with the four pointing in different directions. Choose the version where the defender's forced block is least useful to them.
Building only one crossing. A single crossing is easy for a defender to take away. Build two or three and the defender cannot stop them all.
Four-threes in every direction
The diagram above uses a row and a column because they are easy to see. In real games, four-threes just as often combine a row with a diagonal, or two diagonals. The diagonal versions are the most dangerous in practice, because defenders — and attackers — notice them less. When you look for crossing points, check all six pairs of directions: row–column, row–diagonal, row–anti-diagonal, column–diagonal, column–anti-diagonal and diagonal–anti-diagonal. Many players only ever look at the first pair.
Why beginners miss their own four-threes
It is surprisingly common for a beginner to have a four-three available and not play it. The usual reason is that they are looking for "a four" or "a three", not for one move that does both. A simple habit fixes this: whenever you are about to make a four, glance along the other three lines through the same point. If one of them would become an open three at the same moment, you have found a four-three.
Practice
Against the computer on the home board, set yourself a goal: win one game with a four-three. When you do, replay it from your account and find the move where the crossing first became possible. Then try to win the next game with a four-three that you planned two or three moves in advance.
Frequently asked questions
What is a four-three in gomoku?
A single move that creates a four and an open three at the same time. The defender must block the four, and the three then becomes an unstoppable open four.
Does the four-three work in Vietnamese caro?
Yes. The final five has at least one open end, so it wins under blocked-ends rules too.
How do I stop a four-three?
Occupy the crossing point before the opponent uses it. Once the four-three has been played, it is usually too late.
Is a four-three better than a double three?
It is more forcing, because the four leaves only one reply. A double three gives the defender a little more freedom.
