A pin is useful only when you know what is pinned, what sits behind it, and whether the front piece can afford to move. Calling every aligned piece “pinned” hides the most important distinction. ## Absolute pin: the knight cannot move White to move: ```fen 4r1k1/8/8/8/8/8/4N3/4K3 w - - 0 1 ``` The knight on e2 stands between Black's rook and the white king. Moving it would expose check, so every knight move is illegal. White has only king moves. This is an **absolute pin**: the rules of chess, not merely the value of a piece, hold the knight in place. Before calculating an attack on a pinned defender, check whether the king can step away. Once White moves the king off the e-file, the knight may become mobile again. ## Relative pin: moving is legal but expensive White to move: ```fen 4k3/8/8/8/6b1/5N2/8/3QK3 w - - 0 1 ``` Black's bishop on g4 attacks the knight on f3, with White's queen on d1 behind it. The knight has legal moves because the king is not exposed, but most of them abandon the queen. This is a **relative pin**. That difference changes calculation. In the first position, knight moves can be discarded immediately. Here they must be examined. A forcing knight move could give check, win Black's queen, or create mate and justify the material loss. ## A famous warning: pinned does not mean immobile After **1.e4 e5 2.Nf3 Nc6 3.Bc4 d6 4.Nc3 Bg4**, Black appears to pin the f3-knight to White's queen: ```fen r2qkbnr/ppp2ppp/2np4/4p3/2B1P1b1/2N2N2/PPPP1PPP/R1BQK2R w KQkq - 2 5 ``` The Legal Trap illustrates the danger of trusting that pin blindly. If **5.Nxe5?** is met by the greedy **5...Bxd1?**, White has **6.Bxf7+ Ke7 7.Nd5#**. The knight moved, the queen fell, and Black was checkmated. The trap does not make **5.Nxe5** automatically sound; Black can decline the queen and defend. Its lesson is narrower and more useful: whenever a relatively pinned piece makes a forcing move, calculate checks and mate before counting material. ## A practical pin checklist When pieces line up, ask: 1. Is the rear piece a king, queen, rook, or simply a less valuable piece? 2. Is moving the front piece illegal, costly, or tactically forcing? 3. Can the pinned side break the line with a check, capture, block, or king move? 4. Can the attacker add pressure to the pinned piece before the pin disappears? Set up the first two diagrams and list every legal move of the pinned knight. The contrast is the pattern worth remembering: an absolute pin removes moves; a relative pin changes their price.