Weak squares and outposts

A game on lichess.org, 2014. Black's pawns have advanced to d5 and f5, and between them the e5-square is left. No black pawn can defend it any more: to do so it would have to go back to d6 or f6. White to move.

The knight on e5 stands firm: no pawn will drive it away, and the d4-pawn protects it. Such a square is called an outpost. In this chapter we look at where weak squares come from, why a knight on an outpost can be stronger than the opponent's rook, and how to fight for such squares when the opponent has them.

What a weak square is

A weak square is a square that none of your pawns can defend any more. A pawn captures diagonally forwards, and the square in front of it on the next file is defended while the pawn stands behind it. Once the pawn walks past or disappears in an exchange, the square is left without defence for good: pawns do not move back.

So every pawn move is a long-term decision. A badly placed piece can come back a move later. A pawn pushed without need will leave weak squares behind it until the end of the game. Experienced players move pawns with care and often ask themselves: which squares am I giving away now? This matters most for the pawns in front of your king and the pawns in the centre.

A weak square by itself is not yet a disaster. If the opponent cannot get to it, its weakness stays on paper. A weak square becomes a real problem when a piece can be put on it, and especially when that piece stands in the centre or near the king. And the most dangerous weak square is one where the opponent's piece is protected by their pawn: such a piece cannot be driven away by a pawn and cannot simply be taken.

How do you find weak squares? Look at the opponent's pawns file by file. For each square in front of their pawns, ask: can any pawn on a neighbouring file ever attack it? If the pawns on the neighbouring files have already passed that square or are gone altogether, the answer is “no”, and the square is weak. Start with the centre and the squares near the king: weak squares matter most there. It is useful to do the same for your own pawns: then you know in advance where the opponent will want to put their pieces.

Another name you will meet is a hole. It is used for a weak square in the opponent's camp, especially on the third and fourth ranks from their edge. In the chapter on pawn structure you saw a special case: the square in front of a backward pawn. The pawn cannot go there, the neighbouring pawns have moved on, and an enemy piece occupies the square.

The outpost

An outpost is a weak square in the opponent's camp that your pawn protects. A piece on an outpost stands firm: no pawn will drive it away, and it can only be taken by a piece, at the cost of an exchange. Outposts are usually on the fourth to sixth ranks from your own edge: there the piece already presses on the opponent's camp and is still protected.

The best piece for an outpost is the knight. It moves only a short way, and it needs to stand close to the opponent. A knight on d5 hits eight squares, and half of them are in the opponent's camp. It stops the opponent's rooks from crossing from wing to wing and is afraid of nothing itself. A bishop on an outpost is good too, but for a bishop range matters more than closeness, and it stands well from far away. A rook or a queen needs an outpost less often: a minor piece easily chases them away, and they are strongest on open lines anyway.

The engine knows about outposts. It has a separate term, “Knight outpost”: a knight on the fourth to sixth rank, protected by a pawn, that no enemy pawn can drive away. On the board below the white knight stands on c3. Play Nd5 and watch how the evaluation and its terms change. Then try other moves and make Black's moves too.

After Nd5 a “Knight outpost” row has appeared, about a fifth of a pawn in White's favour. Other terms have grown too: the knight stands better in the centre, and the penalty for the black bishop on e7, which runs into its own pawn on d6, has doubled. That term is called “Bad bishop”. The “Mobility” row has even gone down: from c3 the knight hit more free squares. The evaluation adds everything up, and the outpost outweighs it. Each of these numbers is small, but together they make what players call a positional advantage. It builds up from such details until one of them decides the game.

An outpost in the opponent's camp is valuable even before a piece stands on it. A knight may take several moves to get there, and that is fine: occupying a strong square is worth the time spent if the opponent cannot do anything meanwhile. The classic manoeuvre in the Spanish Game is Nb1–d2–f1–e3 and on to d5 or f5. Four moves with one knight for the sake of one square.

A knight on the sixth rank, on d6 or e6, presses hardest of all. It hits squares on the seventh and eighth ranks, stops the opponent's rooks from connecting and keeps the pawns in front of the king under fire. Russian players call such a knight a bone in the throat. The opponent often gives up a rook for it: losing the exchange is cheaper than putting up with such a knight to the end of the game.

How to use an outpost

A knight on an outpost often gives tactics. It stands close to the opponent's king and heavy pieces, and a jump from there can become a fork or an attack on the queen. In the next two games the knight lands on the same square, d6. In both, Black has no pawn that could defend it: the c-pawn has moved on or vanished, and the e-pawn already stands on e6.

But most often an outpost works without tactics, simply because the knight stands there. It ties down the opponent's pieces: one of them has to watch the squares around the knight all the time, the others cannot go where the knight hits. Sooner or later the opponent gives up a bishop or a rook for the knight just to get rid of it. If you have an outpost, do not hurry: put a piece there and improve your position with the others.

If the opponent trades off the piece on the outpost, check what you will recapture with. It is often better to take with a pawn: the pawn stands on the outpost, presses on the opponent's camp and sometimes becomes passed. That is what happens in the Sveshnikov Variation: after Nd5 Black gives up a bishop for the knight, White takes back with the e4-pawn, and White gets a pawn on d5 that presses on Black's camp.

How to fight for a weak square

A weak square is defended by pieces. So to win it, you have to trade those pieces off or deflect them. The most common method is to trade a bishop for the knight that defends the weak square. The bishop gives up its range, but the square is yours for a long time.

See how it is done in the Sveshnikov Variation. From the very start Black accepts the weak d5-square for the sake of active play, and White fights for it with everything they have.

The fight for a square also goes the other way. If the opponent wants to put a knight on an outpost, trade that knight off in advance, before it gets there, or occupy the outpost with your own piece first. A bishop that hits the outpost square is valuable too: while it is on the board, the opponent's knight will not stand there in peace. So do not hurry to trade such a bishop, even if the exchange looks harmless.

Weak squares are easier to defend against in advance, before they appear. Do not move pawns without a purpose, especially in front of your king. If a weak square is already there, keep a piece near it that defends it, and do not trade that piece without need. And sometimes the best defence is to push a pawn on the neighbouring file and cover the square, even at the cost of a new weakness elsewhere: such a swap can pay off if the opponent cannot use the new weak square.

Weak squares near the king

The most dangerous weak squares are those near the king. The pawns in front of a castled king defend the squares by which the opponent's pieces approach it. The move …g6 weakens f6 and h6, the move …h6 weakens g6, the move …f6 weakens e6 and g6 and the diagonal to the king. While a bishop of one's own stands on g7, the weakening after …g6 is bearable: the bishop itself holds the dark squares. Once that bishop is traded, holes appear around the king.

When no pawns are left in front of the king at all, every square around it becomes weak. The opponent's pieces go where they cannot be driven away, and mate often comes in two moves. There is hardly anything to calculate: it is enough to put the pieces on the weak squares, and the threats appear by themselves.

Weak colour complexes

Sometimes a whole group of squares of one colour becomes weak. This happens when the pawns stand on squares of one colour and the bishop of that colour has been traded. For example, black pawns on c6, d5 and e6 stand on light squares, as in the Semi-Slav Defence. They defend the light squares in front of them, but they hold the dark squares nearby, d6 and e5, poorly: no pawn will ever defend d6 again, and only the f-pawn can defend e5, if it goes to f6. While Black has the dark-squared bishop, this is no disaster. If it has left the board, only the knight and the queen hold the dark squares, and White's pieces can occupy them one after another.

Hence the rule: put your pawns on squares of the colour opposite to your bishop. Then the bishop defends the squares the pawns do not hold, and no weak squares are left. If the pawns stand on the bishop's colour, the bishop becomes bad and the squares of the other colour weak. More about the bad and the good bishop, and about when a knight is stronger than a bishop, is in the chapter “Bishop against knight”.

A weak colour complex is hard to repair: that would mean rearranging the pawns, and pawns do not move back. So such positions are played slowly and patiently. The side with the advantage does not hurry with the attack. It puts pieces on the weak squares one by one, trades off the opponent's pieces that defend those squares, and only then goes for a break. The fewer pieces left on the board that can cover squares of the needed colour, the weaker those squares become. This happens in the French Defence: Black's pawns on e6 and d5 stand on light squares, and in the Winawer Variation, where Black gives up the dark-squared bishop for the knight on c3 of their own accord, White then plays on the dark squares for a long time.

What's next

A knight loves closed positions with firm squares. Rooks need something else: open files by which they get into the opponent's camp, and the seventh rank, where their pawns stand. That is the subject of the next chapter.