The twenty motifs

One piece attacks two things at once, and only one of them can be saved.

The knight is the famous forker because it attacks squares no other piece defends the same way, but every piece forks: a pawn hitting two minor pieces, a queen hitting a rook and a loose bishop, a king in the endgame stepping between two pawns. The test is not "am I attacking two things" but "can both of them get out".

A piece cannot move because something more valuable is behind it.

Absolute when the king is behind it — moving is illegal, not merely bad. Relative when it is a queen or a rook behind, where moving is legal and simply loses material. The follow-up is what wins: a pinned piece is a piece that cannot defend, so pile more attackers onto it, or hit it with a pawn.

A pin the other way round: the valuable piece is in front and has to move.

Check the king along a line with a rook, bishop or queen, and whatever stood behind it is yours when the king steps aside. Skewers are rarer than pins because they need the two pieces already lined up with the valuable one in front — which is why they usually appear after a check has forced the king onto the line.

Moving one piece unmasks an attack from the piece behind it.

The strongest tactic in chess by a distance, because the piece that moves is free to do something of its own while the attack it uncovers does the work. Two threats appear in one move and neither of them can be answered by capturing the moving piece.

The unmasked attack is a check, so the opponent has no time for anything else.

A discovered attack where the piece behind gives check. Whatever the moving piece does — take a queen, walk to a mating square, put itself en prise — the reply must deal with the check first, so it happens for free.

Two pieces give check at once, so the king must move. No block, no capture.

The only tactic against which there is exactly one legal class of reply. Capturing one checker leaves the other; blocking one line leaves the other. This is why double check delivers mates that look impossible — the defender may have five ways to stop each check separately and none that stops both.

Force a defender away from the job it is doing.

A piece is holding a mating square, a back rank or another piece. Attack something it values more, or simply take something it must recapture, and the defence it was providing disappears with it. Often the sacrifice looks absurd until you notice what the recapturing piece stops covering.

Lure a piece — usually the king — onto a square where it can be hit.

Also called the decoy. A sacrifice that the opponent is obliged to accept, played not to win material but to put a piece somewhere fatal: a king dragged onto a fork square, a queen pulled onto a line with a rook. The material comes back with interest a move later.

Get your own piece out of the way of your own attack.

The line or the square is right and your own man is standing on it. Clearance moves it with tempo — usually with a check or a capture, so the opponent has no time to reorganise while the road opens.

Cut the line between a defender and the thing it defends.

Put a piece — often a sacrificed one — squarely between a rook and the square it is guarding. The defender is still on the board, still notionally defending, and no longer able to. Rare, and one of the hardest patterns to see, because the interfering piece usually looks like a blunder.

A piece acts through another piece, along the line it will occupy later.

A rook defending its own piece through an enemy piece, or attacking through one. Nothing is happening yet; what matters is what happens the moment the piece in between moves or is taken. Recognising an x-ray is usually what makes a capture that "loses material" not lose it.

The in-between move: before recapturing, do something more forcing.

German for "intermediate move", and the single most common reason a calculated line turns out to be wrong. You expect a recapture; instead comes a check, or a bigger threat, and by the time the recapture happens the position has changed. Look for one every time a sequence seems forced.

Having to move is itself the problem.

Every legal move makes the position worse, and passing is not allowed. Mostly an endgame idea — king and pawn endings are decided by it — and the reason "the opposition" matters: whoever is obliged to step aside first loses the square. Almost the only situation in chess where the right of a move is a liability.

A king boxed in by its own pawns, mated along the first rank.

The most common mate between players who have castled and left the pawns alone. It rarely appears as a mate on the board — it appears as a threat that wins material, because every defensive move has to keep guarding the rank. The whole family of deflection tactics exists to remove that guard.

A knight mates a king that its own pieces have hemmed in.

The finish of Philidor’s Legacy: queen sacrifice on g8, rook recaptures, knight on f7 delivers mate with the king surrounded by its own men. Rare in real games and worth knowing anyway, because the pattern is what makes you look at a corner and count escape squares.

Something is simply undefended and can be taken.

Not glamorous, and it decides more games than every other item on this list combined. Most losses under 1800 are one player taking a free piece the other stopped watching. The habit that fixes it is checking what is loose — both colours — before every move.

A piece has no safe square, and can be hunted down at leisure.

Usually a bishop that took a pawn it should have left, or a knight that went raiding. The tactic is not a single blow but a squeeze: take away the squares one at a time and the piece falls with no sacrifice needed.

The winning move is not a check, not a capture, and not a threat.

The reason strong players find combinations that others miss. After a forcing sequence the answer is a modest move that takes away the last escape square, and it is invisible to anyone who only calculates checks and captures. If a position looks winning and nothing forcing works, look for the quiet one.

Give material for something worth more than material.

Time, lines, squares, or the position of the enemy king. A real sacrifice is not a gamble; it is a calculation whose end is concrete. What separates one that works from one that does not is almost always whether the defending pieces can come back in time.

A pawn near promotion changes what every other piece is worth.

A pawn on the seventh is not a pawn; it is a queen that has to be watched by something, and that something is no longer free. Most endgame tactics are really about the tension between stopping a pawn and doing anything else.