Relative pin
A relative pin is a pin in which the piece behind the pinned piece is more valuable but is not the king, so the pinned piece may legally move but would lose that piece.
In a relative pin, the piece behind is a queen, a rook or some other valuable piece, not the king. The rules do not forbid the pinned piece from moving. The pin works because moving it would cost something bigger. Whether the pin holds depends on what the pinned piece can gain by moving and what the player behind it would lose.
Because a relative pin is only a threat, it can be broken by a counter threat. The pinned piece might move with check or with a capture that gives your opponent something more important to do than take the piece behind. Always look for those forcing moves before you rely on a pin.
To use a relative pin, line up a bishop, rook or queen with an enemy piece that has something more valuable behind it. To defend against one, you can move the valuable piece away, defend the pinned piece well, or attack the pinning piece. If a trade on the line costs you little, the pin does not hurt.
In the diagram White to move plays Rd1. The rook attacks the knight on d5, and the queen on d8 stands behind it on the d-file. The knight is protected by the queen, so White does not take it. It should not move, because Rxd8+ would then win the queen.
It sits close to Mirror defense. A mirror defense is a strategy where Black copies White's moves, keeping a symmetrical position, and it works only until a concrete tactic or a forcing sequence makes the copying fail.
Compare it with Pin. A pin ties a piece to its square: a bishop, rook or queen attacks it, and stepping aside would expose a more valuable piece standing behind it on the same line.
Compare it with Zwischenzug. A zwischenzug, German for in-between move, interrupts a sequence both sides expect: instead of recapturing or answering a threat at once, a player slips in a check or bigger threat first.
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Related terms
A pin ties a piece to its square: a bishop, rook or queen attacks it, and stepping aside would expose a more valuable piece standing behind it on the same line.
An absolute pin is a pin in which the piece behind the pinned piece is the king, so the pinned piece cannot legally move off the line at all.
A skewer attacks a valuable piece that stands in front of a less valuable one on the same line. The front piece must run, and the piece behind it is then taken.
In a discovered attack one of your pieces steps off a line, and that move unmasks a bishop, rook or queen standing behind it, so a single turn produces two threats.
Guides that go further
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