Connect 4 Is a Solved Game, and the First Player Always Wins
Start in the middle column, and here's why
Staff Writer · · 2 min read
Connect 4 is a solved game, which means that with perfect play from both sides on the standard seven by six board, the first player wins.
This was proved in 1988, independently and within about two weeks of each other, by James Dow Allen and Victor Allis. Allis published it as part of a master's thesis, and the result has stood ever since.
Knowing this doesn't ruin the game, because nobody plays perfectly, but it does tell you what to aim for.
The first move decides it
The forced win requires the first player to open in the center column, and it has to be that specific move.
Open anywhere else and the guarantee disappears. If you open in the second column from either edge, the game is a draw with perfect play, and if you play the outermost column first, the second player can force a win.
So the entire theoretical advantage of moving first rests on one move, and if you take nothing else from this, take the center column.
Why the center matters
Count the ways to make four in a row through each column, and you'll see that the center column participates in more possible four-in-a-rows than any other, because lines through it can extend in both directions.
Pieces in the center are doing more work than pieces at the edge. That's the whole principle, and it holds for the second and third moves too, so keep fighting for the middle.
Odd and even threats
The idea that separates competent players from casual ones is that the row a threat sits on matters.
Because pieces stack from the bottom, a threat is only useful when the square below it gets filled. Broadly speaking, when you're playing first, threats on odd-numbered rows tend to work in your favor, and when you're playing second, even rows do.
If you don't want to think in parities, the practical version is this: pay attention to what your move lets your opponent place on top of it. Handing them the square above yours loses more games than any other single mistake.
The trap everyone falls into
The trap is building a threat that your opponent is forced to block, without noticing that blocking it gives them the exact square they needed.
This is the most common way an obviously winning position evaporates, so before you make a threat, look at what sits directly above it.
Does knowing this help?
Against a perfect opponent it doesn't help at all, but against an actual person it helps quite a lot. Open in the center, contest the middle columns, and check the square above before you commit, and you've got most of the practical game covered.
If you want to test it, Gamebot runs Connect 4 in Discord, which is a low-stakes way to find out whether the center column theory survives contact with your friends.