Weak squares, holes, and colour complexes

Pawns cannot move backwards. That one rule is where weak squares come from, and it is why a square you give away today is still given away in forty moves.

Also called a hole
Cause a pawn move that can never be taken back
Worst case a knight there that cannot be traded

A square is weak when no pawn of yours will ever be able to attack it. Not "is not covered right now": ever. Because pawns cannot move backwards, the moment the pawn that guarded a square advances past it or gets traded off, that square is weak for the rest of the game.

A weak square that an enemy piece can actually reach is usually called a hole. Once a knight sits in one, you cannot chase it with a pawn, which means the only way to remove it is to take it, and taking it usually costs you a better piece. That is an outpost, seen from the other side.

The Najdorf hands over d5 and does it on purpose

The Najdorf Sicilian. Black's sixth move, 6...e5, is one of the most respected moves in opening theory and it creates a weak square on the spot.

1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 6.Be2 e5 7.Nb3 Be7

The white knight on c3 has four legal squares here, and d5 is the one the whole opening is about. Black's c-pawn was traded on move three and the e-pawn has gone past d5 to e5. Neither can come back, so no black pawn will attack d5 again for the rest of the game.

Black accepts this knowingly. In return the e5 pawn takes d4 and f4 away from White's pieces, the dark-squared bishop gets a free diagonal, and Black gets fast play on the queenside. Whether it is a good trade has been argued for seventy years, which is a fair summary of how weak squares work: they are a real cost, not an automatic loss.

A weak square is not a weak pawn

This is the confusion worth clearing up. A weak pawn is a pawn that can be attacked and cannot be defended by another pawn, such as an isolated pawn or a backward pawn. It is a target you can win.

A weak square has nothing on it. There is nothing to win and nothing to attack. What it costs you is the use of that square forever, and the damage arrives later, when a knight lands on it. The two often travel together, because the pawn move that creates the hole is frequently the same one that leaves a pawn backward behind it.

Colour complexes

Weak squares come in families. A pawn move weakens the squares of one colour, and the pawns beside it usually stand on the other colour, so the holes tend to arrive in groups on one colour of square. Play ...g6 and ...h6 and the dark squares round your king are thin; trade off the dark-squared bishop as well and there is nothing left to cover them at all.

That last point is the one that decides games. A colour complex is only serious when the bishop of that colour has gone, because a bishop is the piece that covers squares a pawn no longer can. Before you trade a fianchettoed bishop, look at what colour the squares around your king are, and see good and bad bishops for the other half of that trade.

Every pawn move creates weak squares. The question is only whether they matter.
A hole matters when the enemy can reach it with a knight and you cannot cover it twice.
It matters more in front of your king and less on the far side of the board.
It stops mattering if the position is completely closed or if all the minor pieces come off.
The cure is prevention: see prophylaxis, and think twice before pushing a pawn in front of your own king.

Questions people ask

What is the difference between a hole and a weak square in chess?

They are close to the same thing and most players use them interchangeably. Strictly, a weak square is any square your pawns can no longer control, and a hole is a weak square inside your own territory that an enemy piece can actually occupy. A hole on d5 is a problem; a weak square on h6 that no piece can reach is bookkeeping.

How do I stop creating weak squares?

Move pawns less, and when you do move one, look at the squares it can no longer attack and ask whether an enemy knight can reach any of them. Pawn moves in front of your own king deserve the most suspicion, because those are the holes that turn into attacks rather than into slow endgame problems.

Can a weak square be fixed?

Not by pawns, which is what makes it weak in the first place. You can cover it with pieces, which ties them down, or you can contest it by trading off every piece that wants to land there. The cleanest solution is usually to trade the enemy knight when it arrives, even at the cost of a bishop.

Weak square sits under Pawn structure in the reference. Nearby: