TECHNIQUE 4 OF 4
Forced next-turn wins: test every opposing reply
Two independently playable winning columns are one way to force a win. A stacked threat can work differently: blocking the lower winning square may make another winning square above it playable. The decisive test is what remains after every legal opposing reply.
The rule and its limit
After your proposed move, simulate every legal opponent drop. Reject the forced-win claim if any reply wins immediately for the opponent, draws the game, or leaves you without an immediate winning move. If every reply instead leaves you a winning drop, you have proved a win on your next turn. One familiar pattern creates two winning columns: a single opposing token can block at most one. Another uses stacked winning squares in one column, where occupying the lower threat supplies support for the upper one. Check the actual board after the reply; merely drawing two attractive lines proves neither pattern.
A common mistake
Two gaps above one stack are not two simultaneously playable moves. They can still form a forced sequence if every attempted block enables a verified win above. Conversely, an opponent's immediate win defeats the tactic before you can use either threat.
PLAYABLE EXAMPLE 1
A reply cannot cover every threat
Violet to move. Find a move after which every legal opposing reply leaves you an immediate winning 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
Forced next-turn winning columns: 4. For each qualifying move, every legal reply has been checked, including replies that might win immediately for the opponent. The reply table gives your winning response.
| First move | Immediate effect | Checked consequence |
|---|---|---|
| Column 1 | Lands at R1C1. | No opponent win in one move; no forced next-turn win established. |
| Column 2 | Lands at R2C2. | No opponent win in one move; no forced next-turn win established. |
| Column 3 | Lands at R5C3. | No opponent win in one move; no forced next-turn win established. |
| Column 4 | Lands at R4C4. | Forces a win on your next turn against every legal reply. |
| Column 5 | Lands at R1C5. | No opponent win in one move; no forced next-turn win established. |
| Column 6 | Lands at R5C6. | No opponent win in one move; no forced next-turn win established. |
| Column 7 | Lands at R3C7. | No opponent win in one move; no forced next-turn win established. |
PLAYABLE EXAMPLE 2
Prove the fork against each reply
Orange to move. Find a move after which every legal opposing reply leaves you an immediate winning 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
Forced next-turn winning columns: 3, 4. For each qualifying move, every legal reply has been checked, including replies that might win immediately for the opponent. The reply table gives your winning response.
| First move | Immediate effect | Checked consequence |
|---|---|---|
| Column 2 | Lands at R2C2. | No opponent win in one move; no forced next-turn win established. |
| Column 3 | Lands at R4C3. | Forces a win on your next turn against every legal reply. |
| Column 4 | Lands at R3C4. | Forces a win on your next turn against every legal reply. |
| Column 6 | Lands at R5C6. | No opponent win in one move; no forced next-turn win established. |
| Column 7 | Lands at R2C7. | No opponent win in one move; no forced next-turn win established. |
Two gaps in one column are not a two-column fork
Two of your potential lines need R4C4 and R3C4 respectively. Column 4 is filled through row 5, so R4C4 is its next landing square and R3C4 is above it.
The tempting move
Count the two empty line endpoints as two immediate winning moves.
Why it fails
Only R4C4 is currently playable. A token cannot reach R3C4 while R4C4 is empty, so the claimed second immediate winning drop does not exist.
What you can conclude
There is at most one currently playable threat in that column, so this is not evidence of two independent winning drops. A stacked tactic may still work if blocking R4C4 makes R3C4 an actual winning drop and every other reply also loses. Test those replies before accepting or rejecting the forced-win claim.
Try the idea in another position
After your move, columns 2 and 6 each contain a different currently playable winning drop for you. The opponent has no immediate win and chooses to occupy the winning square in column 2. What is your next tactical check?
Check your reasoning
Check that column 6 still has the legal winning drop and play it. Their column-2 move cannot remove your existing tokens or occupy the current landing square of column 6 in this classic version. The absence of an immediate opponent win is an essential premise.