TECHNIQUE 3 OF 4
Immediate defence: stop the actual winning reply
If you cannot win now, enumerate the opponent's legal one-move wins. A useful block removes the real reply, not merely a square that looks dangerous.
The rule and its limit
Simulate each candidate move and then check the opponent's immediate winning drops. If the opponent has a single currently playable winning square and you have no immediate win, occupying that square is necessary to prevent that particular win. It may not be sufficient if your move opens another threat. Two independent winning columns require more than blocking either one.
A common mistake
Choosing an attractive attack while an opponent can win next turn overlooks the game's immediate outcome. Blindly dropping into a threatening column can also supply support for the opponent's winning square above your token.
PLAYABLE EXAMPLE 1
Remove the immediate danger
Orange to move. There is no immediate win for you. Which columns avoid handing the opponent a win on their next move?
Loading playable study…
Use the column buttons to drop a token. Orange (O) and Violet (V) take turns. You control both sides here; there is no computer opponent. Test a reply, then undo to compare another.
Keyboard: Tab to an enabled control, then press Enter or Space. The study starts from the diagram shown; reload can restore your own saved moves.
Try the task before inspecting the answer.
Compare the starting moves
Columns avoiding an immediate opposing win: 3. This certifies only the next reply; it does not prove that the game can be won or drawn.
| First move | Immediate effect | Checked consequence |
|---|---|---|
| Column 1 | Lands at R2C1. | Opponent can win next in column 3. |
| Column 2 | Lands at R4C2. | Opponent can win next in columns 2, 3. |
| Column 3 | Lands at R3C3. | No opponent win in one move; no forced next-turn win established. |
| Column 4 | Lands at R3C4. | Opponent can win next in column 3. |
| Column 5 | Lands at R5C5. | Opponent can win next in column 3. |
| Column 6 | Lands at R6C6. | Opponent can win next in column 3. |
| Column 7 | Lands at R5C7. | Opponent can win next in column 3. |
PLAYABLE EXAMPLE 2
Compare safe and unsafe drops
Orange to move. There is no immediate win for you. Which columns avoid handing the opponent a win on their next move?
Loading playable study…
Use the column buttons to drop a token. Orange (O) and Violet (V) take turns. You control both sides here; there is no computer opponent. Test a reply, then undo to compare another.
Keyboard: Tab to an enabled control, then press Enter or Space. The study starts from the diagram shown; reload can restore your own saved moves.
Try the task before inspecting the answer.
Compare the starting moves
Columns avoiding an immediate opposing win: 3. This certifies only the next reply; it does not prove that the game can be won or drawn.
| First move | Immediate effect | Checked consequence |
|---|---|---|
| Column 1 | Lands at R5C1. | Opponent can win next in column 3. |
| Column 2 | Lands at R5C2. | Opponent can win next in column 3. |
| Column 3 | Lands at R6C3. | No opponent win in one move; no forced next-turn win established. |
| Column 4 | Lands at R5C4. | Opponent can win next in column 3. |
| Column 5 | Lands at R5C5. | Opponent can win next in column 3. |
| Column 6 | Lands at R5C6. | Opponent can win next in column 3. |
| Column 7 | Lands at R5C7. | Opponent can win next in column 3. |
A supposed block can provide the missing support
Violet has a supported horizontal three at R4C1, R4C2 and R4C3. R4C4 and R5C4 are empty, while R6C4 is occupied. Orange is considering a drop in column 4.
The tempting move
Drop in column 4 to block Violet's gap at R4C4.
Why it fails
Orange lands at R5C4. That supplies the missing support, so Violet can next drop at R4C4 and complete the horizontal four, unless Orange's own move has already ended the game.
What you can conclude
The move does not occupy the intended blocking square. Check for an immediate Orange win or another plan; do not turn an unplayable enemy gap into a playable winning reply by mistake.
Try the idea in another position
The opponent can win on the next move by landing at R6C7. You have no immediate winning drop. Why must you consider column 7, and what should you check after simulating that block?
Check your reasoning
Dropping in column 7 occupies R6C7 and prevents that specific winning placement. Then enumerate the opponent's legal replies again: a different winning column or the newly available square above may still defeat you. Blocking one threat is not proof of a safe position.