Connect Four

How to play

Pick a column and your disc falls to the lowest free slot in it. Line up four of your colour in a row, a column or a diagonal to win, and a full board with no line is a draw. Play a friend on the same device or take on the computer at three strengths. Hard searches several moves ahead, so it will spot your threats and set up its own. You always move first, which is a real advantage in this game.

Tips

• Open in the middle column. Discs there belong to more possible lines than anywhere else on the board.
• Watch your opponent's threats before building your own. One unanswered three in a row ends the game.
• Build a double threat, where a single move creates two separate ways to make four. Only one can be blocked.
• Count the empty squares under a threat. A gap you can only complete by handing over the square above it is worthless.
• Avoid stacking directly on top of a square that would give your opponent four. Every disc you drop hands them the slot above.

Also a solved game

Connect Four was sold by Milton Bradley in 1974 and solved by computer in 1988, independently by James Allen and Victor Allis. The result: on the standard seven column, six row board, the first player wins with perfect play, and the winning first move is the centre column. Any other opening lets the second player draw or win. That is why the tips say to open in the middle, and why you always move first against the computer here.

Knowing the game is solved does not tell you how to win it, because the perfect strategy is far too large to memorise. The practical version is about threats: squares that would complete four for you, and who is forced to play under them.

Playing for threats

• The centre column is the strongest square on the board. It belongs to more possible lines than any other.
• A threat is a square that completes a line for you. Create one your opponent must block, then create a second while they do.
• Two threats stacked in the same column, one above the other, is usually decisive: blocking the lower one hands you the upper one.
• Count the empty squares below a threat. If the square under it is empty, whoever is forced to fill it loses the square above.
• Zugzwang wins endgames. When the board fills, the player who is forced to move under an enemy threat loses, so aim to have the spare moves.

Common questions

Who wins with perfect play?

The first player, by opening in the centre column. The game was solved in 1988. You move first against the computer here.

What is the best first move?

The centre column. Every other opening allows the second player at least a draw.

How strong is Hard?

It searches several moves ahead and will see and block your threats, so beating it usually needs a double threat rather than a single one.