How to win at Connect Four

The grid is 7 columns wide and 6 rows tall: 42 squares, so 21 discs each if it fills up. You drop a disc into a column and it falls to the lowest empty square. Four of yours in a line, across, up or diagonally, wins.

There are 69 different lines of four on the board: 24 across, 21 up and 24 diagonal. Every one of them is a way to win, and every square sits in a different number of them.

Count the lines of four that pass through each square and the centre wins easily. A corner square is part of 3 lines. The bottom square of the centre column is part of 7, and the two middle squares of the centre column are part of 13 each.

Add up a whole column and the centre is in 60 line-slots against 24 for an edge column. A disc in the middle simply does more work. Start there, and keep taking centre squares while they're useful.

A threat is an empty square that would finish a line of four for you. A single threat is easy to block. Two at once usually isn't: if you can make a move that opens two winning squares, your opponent can only cover one.

The other half of the game is the square underneath. If your opponent needs a square that's still floating, don't drop a disc into the square below it, because that hands them the spot. The same works for you: a threat with an empty square beneath it is safe until someone is forced to fill that square.

• Before every move, check whether they have a win next turn. If they do, block it.
• Then check whether your move puts a disc under one of their threats.
• Only then look for your own best move.

Number the rows 1 to 6 from the bottom. Late in a game, when most columns are full, the players end up filling the remaining squares in turn, and that decides who gets which row.

As a rule of thumb, the player who went first wants threats on odd rows (1, 3 and 5), and the player who went second wants them on even rows (2, 4 and 6). A threat on the right row tends to come good at the end, when your opponent runs out of safe moves and has to play under it.

• Opening on the edge. An edge column takes part in far fewer lines than the middle.
• Only watching lines across. Diagonals are the ones people miss, especially ones that climb from right to left.
• Blocking a three that can't become four anyway. If both ends of a line are taken or off the board, it's not a threat.
• Filling the square under your own threat, which just lets them block it.
• Moving fast at the end. With six squares left, count every column before you drop.

Yes. In 1988 James D. Allen and Victor Allis each showed, independently, that the first player wins with perfect play by starting in the centre column. Start anywhere else and perfect play leads to a draw or a loss.

That proof needs a computer to follow. For a human the useful part is shorter: go first, take the centre, and make your threats on odd rows.

On ScampLabs the computer has three levels. Easy drops discs at random, leaning toward the middle columns. Medium does the same but always takes a winning move and always blocks yours when it can see one. Hard looks 5 moves ahead, its own and yours.

Medium is a good place to practise threats, because it only sees one move ahead: set up two at once and it can't stop both. Hard will punish a disc dropped under your opponent's threat.

It’s free in your browser, with no sign-up. Play Connect Four against the computer, with a friend on the same screen, or with someone online.

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