Double attack and the fork

The white king stands on f1, a white rook on d1, and between them the square e1 is empty. A black pawn on e3 steps forward to e2 and hits both squares at once: the king is in check, the rook is attacked. The king has to move, and next move the pawn takes the rook and becomes a queen. A pawn worth one point has won a rook.

This position comes from a real game, and we will come back to it at the end of the chapter. At the end of the chapter on piece values we stopped at a simple fact: a strong opponent does not leave pieces hanging. Attack their rook and they move it. Attack an undefended bishop and they defend it. One threat can almost always be met with one move. So you need two threats, both made with a single move. That is where tactics begins.

One threat and two

A move that makes two threats at once is called a double attack. The opponent can parry one of them, but they have only one move, and the other threat is carried out. When a single piece hits both targets, the double attack is called a fork: the piece spears two targets at once, like the two prongs of a fork. People say it mostly of knights and pawns, but any piece can fork, even the king.

The strongest fork is one where one of the targets is the king. A check must be answered at once, and the opponent has no move left for the other target. You know the answers to a check from chapter 5: move the king, block, or capture the checking piece. If none of them also saves the second target, it is lost.

Compare two moves in the position below. Qf3 also attacks the rook on a8, along the long diagonal. But that is one threat, and Black has time: the rook leaves a8, and the queen is attacking an empty square. The move we are looking for does the same and gives check as well. Black has to spend their move on the king, and the rook stays where it is, still attacked.

What makes a target

A double attack wins only if the opponent cannot save both targets, so choose them with care. Good targets are:

• the king: a check has to be answered, and there is no move left for the other target;
• an undefended piece: you take it for free; it is the hanging piece you already know;
• a piece worth more than the attacker: a knight attacks a rook, even a defended one, and after you take the rook and they take your knight back, you have won the exchange;
• a mating threat: it has to be answered just like a check. Mating threats get their own treatment in the chapter on mating patterns.

Two pieces that are defended and worth no more than the attacker make poor targets. The opponent simply leaves them where they are: you take one, you lose your own piece, and it is an ordinary trade.

The knight

The knight is the great forker. It attacks up to eight squares at once, in every direction, and its attack cannot be blocked: there are no squares between a knight and its target to put a piece on. And a knight attacks a queen or a rook without standing on their lines, so they cannot hit it back.

A simple trick helps you find the knight's forking square: look from the targets, not from the knight. Which square is exactly a knight's move from both targets? If there is one and your knight can reach it in one move, the fork is ready.

When a knight attacks the king, the queen and a rook all at once, it is called a family fork: the whole family is under attack. Find one yourself.

Now the same fork in a real game, with extra pieces around. The black knight on e3 sits in White's camp and looks dangerous, and the queen on d7 waits calmly. The knight on e4 is looking at a square from which it would see both the king and the queen.

The knight has its favourite squares. While the black king is on e8 and the queen and rooks are at home, Black's weak points are c7 and f7. From c7 a white knight attacks the king on e8 and the rook on a8; from f7 it attacks the queen on d8 and the rook on h8. White's matching squares are c2 and f2. That is why, after a slip in the opening, a knight so often lands on exactly those squares, and why castling, which takes the king off e8, also takes one of those forks away. Before you move a piece that guards c7 or f7, check whether an enemy knight is one jump away from them.

The pawn

The pawn is the cheapest piece, and that is exactly why its fork is the most dangerous. Every piece is worth more than a pawn, so the pawn does not care whether its targets are defended. Two pieces standing on the same rank with one square between them, like c6 and e6, are a ready target for a pawn that lands between them, on d5.

A pawn fork with check is stronger still: the opponent has to save the king and does not even get to choose which piece to save.

Pawn forks turn up as early as the opening, and one of them has a name: the fork trick. Black gives a knight for a pawn, then attacks two white pieces with a pawn and gets the knight back. It wins nothing, but it is a useful trade: Black removes White's centre pawn and puts their own there.

Look at the move before the fork. Black did not wait for White's pieces to step onto the right squares by themselves: by capturing on e4, they invited the white knight to e4. We will come back to this idea, luring a piece onto the forking square, at the end of the chapter.

The queen, bishop, rook and king

The queen attacks in all eight directions and has more forks than any other piece: you saw Qd5+ at the start of the chapter. But the queen is the most valuable piece, so its fork wins only against undefended pieces or together with a check. Bishops and rooks fork less often: the bishop attacks only along diagonals, the rook only along ranks and files, and the targets have to stand on those lines. When they do, the blow is just as hard to meet.

The fork a beginner most often loses a piece to is a queen fork with check: the king stands on an open diagonal, and an undefended bishop or rook is idling on the far side of the board. The enemy queen arrives from afar, as in the first exercise of this chapter, and wins time with the check. So before every move it pays to ask: what checks does the opponent's queen have, and what else does it attack from those squares?

In the endgame, once the queens are off, even the king forks. It attacks every square next to it, and if two enemy pieces stand next to the same square, the king goes there. The one condition is that the square itself is not attacked: the king never steps onto a square the opponent attacks.

When a fork fails

Not every move that hits two targets wins. Before you fork, ask yourself three questions.

1. Can the forking piece be taken? A knight that jumps up to the king may land where the king attacks it, and a pawn may land where another pawn attacks it.
2. Do the targets defend each other, or does something else defend them? Then it is a trade, as with the two bishops above.
3. Does the opponent have a move with a threat of their own? A check, a capture or a mating threat in reply, and they gain the time to save both pieces. Such a reply is called an in-between move, and it has a chapter of its own.

See what the engine says about a fork that fails the first question.

The king attacks every square next to it, and ...Kxc7 takes the knight for free. A fork on a square the opponent defends is just a gift.

The third question is the trickiest. The fork is on, both targets are attacked, but the opponent answers with a check of their own or takes something valuable with a threat. While you deal with their move, they rescue the second piece, and the fork comes away empty-handed. That is why strong players, having found a fork, look half a move further: which checks and captures will the opponent have once the piece stands on the forking square?

Setting up a fork

In a game the targets rarely stand exactly where your piece can reach them. Then you put them there yourself. There are two ways, and both rely on the force of forcing moves.

Drive with checks. The king must step out of check, and if it has few squares to go to, the check drives it to where the fork is waiting. The knight is especially good at this chase: its checks cannot be blocked.

Lure with a sacrifice. The enemy piece is on the wrong square? Offer it something to take, so that once it takes, it stands where you want it. Giving up material to get more back is a sacrifice; sacrifices and decoys are covered in chapter 15 and chapter 19.

Sometimes the target is in the right place but defended by a piece you can remove. That is removing the defender, and it too has its own chapter. See how it clears the way for a fork.

How to spot them

You do not hunt for forks blindly: you see them in how the pieces stand. Make a habit of three looks at the board before every move:

1. What does the opponent have undefended? Where are their king and queen?
2. Are there two such targets that one of your pieces can hit from one square? For a knight, look for a square a knight's move from both targets; for a pawn, two pieces on one rank with a square between them; for the queen, a square from which both targets are in sight along lines or diagonals.
3. Can you get there with a check, a capture or a sacrifice, and can your piece be taken there?

Give your own pieces the same look: where do they stand so that one blow could hit two of them? Undefended pieces are the first targets of any fork. Practise spotting them.

Now back to the pawn from the start of the chapter. Find its move yourself.

And the last puzzle, the hardest. Here the fork hides behind a queen trade, and to see it you have to notice why the pawn on c6 cannot capture.

Apart from three teaching "find the move" exercises in the early sections, every puzzle in this chapter comes from a real game played on lichess.org in January 2014. There are more like them, with a rating that grows as you do, on the Practice page, under the theme "Fork".

What's next

A fork attacks two targets, and the opponent saves one. But sometimes there is nothing to save with: the target is attacked and cannot move, because a king or a queen stands behind it. You saw this in the last puzzle: the pawn on c6 could not take the queen, because it would have exposed its king to check. That is a pin, and in the next chapter you will learn to set one up, to use it and to get out of one.