Connect Four looks like a children’s game and is a solved one — the first player wins with perfect play, proved independently by James Allen and Victor Allis in 1988. Between those two facts sits a genuinely interesting game, and three ideas cover most of it.
Why the centre column is worth so much
Count the ways to make four in a row on a seven-by-six board. There are 69 of them: horizontal, vertical and both diagonals.
Now count how many pass through each column. A square in the centre column takes part in up to 13 of those lines. A square in an outer column, only 3.
That ratio is the entire opening theory. Discs in the centre are simply working harder than discs anywhere else, and a player who owns the middle three columns will find threats appearing without having planned them.
It is also why the game is a first-player win: opening in the centre column is strong enough to be decisive with perfect play on both sides.
Most games are lost, not won
The most common way to lose is not failing to see a threat. It is creating one for your opponent.
Every disc you drop makes the square above it playable. If that square would complete four for the other side, you have handed them the game — and you did it voluntarily.
Before every move, look at the square directly above the one you are about to fill. That single check, done consistently, is worth more than any amount of offensive planning. Strong players spend more time on it than on their own threats, because a good position thrown away by one gift is indistinguishable from a bad position.
The corollary: when your opponent has a threat you cannot block, look for a column where filling it does not help them, rather than blocking reflexively.
Double threats
Any single threat gets blocked. Winning therefore means creating two at once.
The classic shape is a horizontal three with open squares at both ends:
. . X X X . .Both ends complete four, only one can be blocked. Building toward this shape — rather than toward any specific four — is what offence in Connect Four actually looks like.
The other common double is a three where one completion is horizontal and another is diagonal through the same disc. These are harder to see and harder to defend, which is why diagonal play is where the game gets interesting.
Parity
Once you have stopped hanging pieces, parity is the next layer.
Because discs stack from the bottom, the row a threat sits on determines who gets there first. On a seven-column board, if both players keep filling columns evenly, the odd-numbered rows (counting from the bottom) tend to fall to the first player and the even-numbered rows to the second.
The practical version: if you moved first, aim your threats at odd rows. If you moved second, aim at even rows. And when your opponent has a threat on a row that favours them, try to change the parity of that column by forcing a move into it.
This is where club-level Connect Four separates from casual play. You do not need to calculate it precisely — just noticing which rows your threats are landing on will change how you choose between two otherwise equal moves.
Playing the bot
The hard bot on our version searches five moves ahead with alpha-beta pruning and evaluates threats plus centre control. It will take any win it can see and block any single threat, so beating it means building a genuine double.
The easy bot plays randomly but still takes immediate wins and blocks immediate losses — a bot that misses those is not easy, it is broken, and playing against one teaches nothing.
There is also a pass-and-play mode, which is where parity actually starts to matter, since a human opponent will punish you for ignoring it in a way neither bot reliably does.