Hex

Join Your Two Edges

The board is a rhombus of hexagons. Two of its sides are red and two are blue. Players take turns placing one stone of their colour on any empty cell. Red wins by building an unbroken chain of red stones joining the two red sides; blue wins by joining the two blue sides. Stones are never moved, never captured, and never removed. Red plays first. That is the whole game.

Six Neighbours, Not Eight

Each hexagon touches six others. That is what makes the game work, and it is worth a moment because a square grid would not. On a square board, two paths crossing diagonally can pass through each other — so both players could complete a connection, and a draw would be possible. Hexagons have no diagonals. Two chains either meet or they do not, and that is exactly why exactly one player always connects.

The Swap Rule

Because the first player wins with perfect play, Hex is played with a balancing rule. After red places one stone, blue may either answer normally or take that stone, becoming red and leaving red to move. This is sometimes called the pie rule, after the childhood method of one child cutting the cake and the other choosing a slice: it makes red's opening a genuine decision, because an opening too strong will simply be taken. Red's real task on move one is to find a stone that is not worth stealing. On Cognivo the swap is offered as a move on red's stone — click it.

The Bridge

Two stones placed a short step apart, with two empty cells touching both of them, are already connected — even though they are not touching. If your opponent takes one of the two cells, you take the other. They cannot have both. This is called a bridge, and learning to see it is the single biggest jump in Hex strength. It lets you cross the board in half the stones, and it means a chain that looks full of gaps may be unbreakable. Most strong play is the construction of bridges rather than solid chains.

Ladders, And Escaping Them

When you push toward your edge and your opponent blocks alongside, and you push again and they block again, the pair of you run a ladder across the board. Ladders are forced sequences, and the player running them gains nothing by continuing — the outcome was decided before the first step. What decides a ladder is whether there is a friendly stone waiting where it ends. A single stone placed far away, long before the ladder starts, can make the whole sequence win instead of lose. This is called a ladder escape, and it is why strong players place stones that appear to do nothing.

The Short Diagonal

The centre is strong for the ordinary reason — it touches more of the board — but Hex has a second and more specific idea. The shortest line between your two edges runs along one diagonal of the rhombus, and it is the natural spine of your connection. Your opponent's spine is the other diagonal, and the two cross in the middle. That crossing is why the centre cell is the strongest opening, why it is always taken under the swap rule, and why the fight in a serious game happens in a band across the middle rather than near the edges.