Discovered Check and Double Check: Why They Are So Strong

A check is usually given by the piece that just moved. A knight jumps and checks, a rook swings over and checks. Sometimes, though, the check comes from a piece that didn’t move at all. It was standing behind the piece that moved. That is a discovered check. And if the piece that moved also gives check, two pieces are checking at once. That is a double check.

Both are known as some of the strongest tactics in chess. In this post I explain why, using two positions. Each one was checked with a program to confirm that the moves are legal and give exactly the check I describe.

Check in the rules

In the FIDE Laws of Chess, Article 3.9.1 says the king is “in check” if it is attacked by one or more of the opponent’s pieces. Article 3.9.2 says no piece can be moved that will either expose the king of the same colour to check or leave that king in check.

The words “discovered check” and “double check” don’t appear in the Laws. They are names for ways a check can arise. But since the article covers a king attacked by “one or more” pieces, a double check is, as far as the rules go, simply a check.

There are three ways to get out of check: move the king, capture the checking piece, or put a piece in between. I wrote about them in Check vs Checkmate. Which of the three is available is exactly what makes these two patterns strong.

Discovered check

The English Wikipedia article Discovered attack describes a discovered attack as an attack revealed when one piece moves out of the way of another, and says that if the discovered attack is a check, it is called a discovered check.

The piece behind has to be a long-range piece: a queen, a rook or a bishop. The piece in front can be anything.

What makes it strong is that the front piece gets to do something useful while it steps aside. Your opponent has to deal with the check first, so whatever the front piece is threatening, there is no time to answer it.

Position 1: White: king g1, rook e1, knight e4, pawns f2, g2, h2. Black: king e8, queen a4, pawns a7, b7, f7, g7, h7. White to move.

White’s rook and Black’s king are on the same e-file, and the only piece between them is White’s own knight. Once the knight leaves e4, the rook gives check.

White plays Nc5+. The knight itself doesn’t attack the black king. The check comes from the rook on e1. Meanwhile the knight on c5 attacks Black’s queen on a4.

Black has only three legal moves: Kf8, Kd8 and Qe4. Kd7 is covered by the knight on c5, and Ke7 by the rook. If the king moves, White plays Nxa4 and takes the queen. If Black blocks with Qe4, White simply captures the queen there. Whatever Black chooses, the queen is lost.

If the knight had attacked the queen without a check, Black would just move the queen away. Because the attack comes together with a check, there is no move left for that.

Double check

If the front piece steps aside and also gives check itself, two pieces are checking at the same time. That is a double check. The English Wikipedia article Double check states that the only possible reply to a double check is a king move.

The reason is simple. With two checking pieces, capturing one leaves the other still giving check. Blocking one line leaves the other line open. One move can’t remove both, so the only defence left is to move the king.

Position 2: White: king g1, rook e1, knight e4, pawns a2, b2, c2, f2, g2, h2. Black: king e8, queen d8, rooks a8 and h8, knight b8, bishops c8 and f8, pawns a7, b7, d7, f7, g7, h7. White to move.

The material isn’t balanced here. Just look at the squares around Black’s king. d8 holds Black’s own queen, f8 Black’s own bishop, and d7 and f7 Black’s own pawns. The remaining square, e7, is on the e-file, inside the rook’s line.

Now Nd6 is checkmate. The knight on d6 checks the king on e8, and at the same time it opens the check from the rook on e1.

It looks as if Black can capture the knight. The bishop on f8 reaches d6 through e7, so Bxd6 seems possible. But after Bxd6 the rook’s check is still there, so the move is illegal. Blocking the rook with Qe7 or Be7 leaves the knight’s check in place. The king has no square, so it is mate.

If White’s rook were not on the e-file and only the knight were checking, Black would just play Bxd6. The same knight move becomes mate only because of the rook behind it.

In this position Nf6 is also mate, for the same reason. A knight on f6 also attacks e8, and the rook’s check opens too. Black can’t take on f6 with the g7 pawn either.

Mate puzzles and double check

The “only the king can move” property fits mate puzzles very well. With an ordinary check, you have to read captures and blocks as well. With a double check, you only read the king’s squares. If every one of them is covered, you already know it’s mate.

A famous example is the game Réti vs Tartakower, Vienna 1910, which the Wikipedia article on double check also describes. White sacrificed the queen with 9.Qd8+, Black took with 9…Kxd8, and then 10.Bg5+ was a double check: the rook on d1 and the bishop on g5 check together. After 10…Kc7 comes 11.Bd8#, and after 10…Ke8 comes 11.Rd8#. Either way it is mate. This sequence was also checked with a program.

Giving up even a queen to reach a double check, so that the opponent’s only option is to move the king: this is one reason sacrifices show up so often in mate puzzle solutions.

How it differs from a pin

A discovered check looks a lot like a pin. In both, a long-range piece and the enemy king stand on one line with a single piece between them.

The difference is whose piece is in the middle. If it belongs to your opponent, it can’t move, and that is a pin. If it is your own, it can step aside whenever you like and give a discovered check. I wrote about pins in Basic Chess Tactics: Fork, Pin and Skewer.

The same idea in shogi

Shogi has the same patterns. The Japanese Wikipedia article on 王手 (check) calls a check made by moving your own piece off the line of a ranging piece (rook, bishop, lance, dragon or horse) an “aki-ōte” or “hiraki-ōte”, and a check given by two pieces at once a “ryō-ōte”. It also says that against a ryō-ōte no piece can be dropped in between, and the only option is to move the king.

These are almost exactly discovered check and double check. The piece behind is a ranging piece, and against two checks only the king can move. If you play shogi, your feel for these patterns carries straight over to chess.

The difference is what happens to captured pieces. In shogi you can drop them back on the board. In chess you can’t. So in chess, winning a big piece with a discovered check, as in Position 1, is a pure material gain. Other differences between the two kinds of puzzles are in Tsume Shogi vs Chess Mate Puzzles.

How to spot them

Beginners often miss a discovered check even when it is there, because the piece that moves and the piece that checks are different. Look at the board in this order.

First, draw lines from your queen, rooks and bishops toward the enemy king. Check whether any of them meets the king along a file, rank or diagonal.

Second, count the pieces on that line. If the only thing in between is one of your own pieces, a discovered check is ready.

Third, think about where that front piece can go. Look for a square where it attacks the queen or a rook, captures something, or gives check itself. If it can give check too, that’s a double check, and then you only need to count the enemy king’s squares.

The same view works in defence. If one of your opponent’s pieces stands alone between their long-range piece and your king, a check arrives the moment it moves. I also wrote about the order for finding candidate moves in Checks, Captures, Threats.

Looking for discovered checks in Chess365

Chess365 is a mate puzzle app with 1,000 puzzles each of mate in 2, 3, 4 and 5. You always play White, and any legal move can be played. Black answers with the defence that lasts longest, and if you don’t mate within the move count, the attempt fails. You have three retries.

Puzzles with a discovered or double check aren’t many. That is exactly why it pays to stop when one of your own pieces stands alone on the line of your rook or bishop, and consider moving it out of the way. Looking at checks first makes these easier to find.

A hint lights up the piece to move and the square it goes to. You still make the move yourself. If the lit piece doesn’t attack the enemy king, look at what stands behind it. After solving, “Review moves” lets you step back and forward one move at a time, so you can see which piece was giving check.

Every puzzle is free to solve, and a one-time Remove Ads purchase turns the ads off. How to read mate in 2 is in Chess Checkmate Puzzles for Beginners, and how to use the app is in Getting Started with Chess365.