Quick answer
Relative Pin is a tactical idea: a line piece pinned to the king. Work from the first evidence position for Relative Pin, and begin by testing Nb8.
Begin from Nb8 in 8/3n1k2/8/8/8/8/8/5BK1 b - - 5 3. Start with the forcing geometry: checks, captures, threats, defenders and flight squares around the target. The evidence answer is: Relative Pin: check whether the pinned defender can legally move and what happens after the capture. Candidate line: Nb8.
In the Relative Pin example, notice: side Black; pieces Black knight d7, Black king f7, White bishop f1, White king g1; legal first moves Nb8, Nf8, Nf6, Ne5, Nc5, Nb6, Ke8, Kf8. Keep the piece census tied to this diagram—other positions with the same theme can look completely different.
The tactical trigger
The first evidence board tests a line piece pinned to the king; the second board tests a line piece pinned to the king. For the pair of examples, install A from direct FEN setup and install B from direct FEN setup. The Chess Wiki and the Tactics hub collect the shared vocabulary. Then compare Candidate Moves with Family Fork, Cross Pin, X Ray Attack around a decoy square.
The two inventories make the distinction concrete. A contains side Black; pieces Black knight d7, Black king f7, White bishop f1, White king g1; legal first moves Nb8, Nf8, Nf6, Ne5, Nc5, Nb6, Ke8, Kf8; B contains side White; pieces Black knight d7, Black king f7, White bishop a4, White king e2; legal first moves Bb5, Bc6, Bxd7, Bb3+, Bc2, Bd1, Kd3, Ke3. Compare the side to move before comparing the labels in the context of the move that closes counterplay.
Topic dossier for this page and board pair r1:8 | r2:3n1k2 | r3:8 | r4:8 | r5:8 | r6:8 | r7:8 | r8:5BK1 / r1:8 | r2:3n1k2 | r3:8 | r4:8 | r5:B7 | r6:8 | r7:4K3 | r8:8: start with a decoy square; then test the move that closes counterplay; keep the order of checks before captures separate from the loose unit behind the target; use the defender carrying two jobs as the transfer check; and reserve the line revealed after clearance for the exception.
Calculation order
On the first board, calculate Nb8 after Nb8 and write down the opponent's best reply around a decoy square. On the second board, calculate Bxd7 after Bxd7 and check the move that closes counterplay. Calculate the most forcing move first, then test the opponent's best capture, interposition or counter-check before naming the motif. In this case the useful condition is the line revealed after clearance.
Key claim: Relative Pin is illustrated here by a line piece pinned to the king; the first concrete test is Nb8. The board anchor is 8/3n1k2/8/8/8/8/8/5BK1; the example is intentionally narrower than the topic label and should not be generalised without checking the surrounding position..
Practical boundary: To answer “How can a player recognize relative pin, calculate the winning idea, and test the defender's best resource?”, compare the recorded setup with Bxd7 and the opponent's reply. The decision is useful only when the stated condition survives that concrete test on board 8/3n1k2/8/8/B7/8/4K3/8. The evidence records Illustrative evidence for the stated mechanism; it is not a claim that the candidate move is forced or best in every position and the second board signature r1:8 | r2:3n1k2 | r3:8 | r4:8 | r5:B7 | r6:8 | r7:4K3 | r8:8. The false-positive test is whether the order of checks before captures appears without the loose unit behind the target, so the conclusion is useful only when the stated condition survives that concrete test.
Evidence positions
example-1: a line piece pinned to the king
Show answer
Relative Pin: check whether the pinned defender can legally move and what happens after the capture. Candidate line: Nb8.
Why this position is here: Relative Pin is represented by a line piece pinned to the king. This is a direct FEN setup with board anchor 8/3n1k2/8/8/8/8/8/5BK1; no opening history is inferred from the diagram.
FEN: 8/3n1k2/8/8/8/8/8/5BK1 b - - 5 3
Question: What is the first concrete decision in this relative pin position?
Answer cue: Relative Pin: check whether the pinned defender can legally move and what happens after the capture. Candidate line: Nb8. The first candidate to test is Nb8. Replay Nb8 on board anchor 8/3n1k2/8/8/8/8/8/5BK1 and write down what changes after it.
Evidence boundary: Illustrative evidence for the stated mechanism; it is not a claim that the candidate move is forced or best in every position.
example-2: a line piece pinned to the king
Show answer
Relative Pin: check whether the pinned defender can legally move and what happens after the capture. Candidate line: Bxd7.
Why this position is here: Relative Pin is represented by a line piece pinned to the king. This is a direct FEN setup with board anchor 8/3n1k2/8/8/B7/8/4K3/8; no opening history is inferred from the diagram.
FEN: 8/3n1k2/8/8/B7/8/4K3/8 w - - 4 3
Question: What is the first concrete decision in this relative pin position?
Answer cue: Relative Pin: check whether the pinned defender can legally move and what happens after the capture. Candidate line: Bxd7. The first candidate to test is Bxd7. Replay Bxd7 on board anchor 8/3n1k2/8/8/B7/8/4K3/8 and write down what changes after it.
Evidence boundary: Illustrative evidence for the stated mechanism; it is not a claim that the candidate move is forced or best in every position.
example-3: a line piece pinned to the king
Show answer
Relative Pin: check whether the pinned defender can legally move and what happens after the capture. Candidate line: Ke8.
Why this position is here: Relative Pin is represented by a line piece pinned to the king. This is a direct FEN setup with board anchor 3k4/8/1n6/8/8/3B4/3K4/8; no opening history is inferred from the diagram.
FEN: 3k4/8/1n6/8/8/3B4/3K4/8 b - - 5 3
Question: What is the first concrete decision in this relative pin position?
Answer cue: Relative Pin: check whether the pinned defender can legally move and what happens after the capture. Candidate line: Ke8. The first candidate to test is Ke8. Replay Ke8 on board anchor 3k4/8/1n6/8/8/3B4/3K4/8 and write down what changes after it.
Evidence boundary: Illustrative evidence for the stated mechanism; it is not a claim that the candidate move is forced or best in every position.
Reading the line
Read the first example (id example-1) as a complete record: continuation Nb8, source fide-laws. This is a direct FEN setup with board anchor 8/3n1k2/8/8/8/8/8/5BK1; no opening history is inferred from the diagram. If A does not expose a line piece pinned to the king, correct the evidence before relying on the prose.
Read the second example (id example-2) separately: continuation Bxd7, source fide-laws. Its feature is a line piece pinned to the king; inventory side White; pieces Black knight d7, Black king f7, White bishop a4, White king e2; legal first moves Bb5, Bc6, Bxd7, Bb3+, Bc2, Bd1, Kd3, Ke3. Compare what changes between Nb8 and Bxd7.
The defensive resource
The main mistake to avoid with Relative Pin is spotting a familiar motif but failing to test the defender's strongest legal resource. In A, the missing condition must be located in r1:8 | r2:3n1k2 | r3:8 | r4:8 | r5:8 | r6:8 | r7:8 | r8:5BK1 after Nb8; in B, test it against r1:8 | r2:3n1k2 | r3:8 | r4:8 | r5:B7 | r6:8 | r7:4K3 | r8:8 after Bxd7.
For Relative Pin, the first board's evidence boundary (after Nb8) is Illustrative evidence for the stated mechanism; it is not a claim that the candidate move is forced or best in every position. The second board's evidence boundary for Relative Pin is Illustrative evidence for the stated mechanism; it is not a claim that the candidate move is forced or best in every position. If a trusted source or careful calculation changes the conclusion around the defender carrying two jobs, update both the evidence record and this article.
Practice from a real game
cover the answer, list checks and captures, and record the defender or escape square that decides whether the idea works. Start with A's side to move and r1:8 | r2:3n1k2 | r3:8 | r4:8 | r5:8 | r6:8 | r7:8 | r8:5BK1; record two candidates, the reply to Nb8 and the correction. Repeat with B's side to move and r1:8 | r2:3n1k2 | r3:8 | r4:8 | r5:B7 | r6:8 | r7:4K3 | r8:8; the changed board tests transfer rather than diagram memory.
After the drill, compare your notes with Family Fork, Cross Pin, X Ray Attack through the loose unit behind the target. Keep A's rejected alternative beside B's chosen line Bxd7; this shows whether the conclusion survived a new board signature.
Sources and scope
Sources for Relative Pin: 1chess.online editorial scope, FIDE Laws of Chess. Source ids are original-analysis, fide-laws. Primary evidence hook: fide-laws. Comparisons and practice notes are editorial. Evidence revision: 2026-08-remediation-r2.
Scope note for board pair r1:8 | r2:3n1k2 | r3:8 | r4:8 | r5:8 | r6:8 | r7:8 | r8:5BK1 / r1:8 | r2:3n1k2 | r3:8 | r4:8 | r5:B7 | r6:8 | r7:4K3 | r8:8: this page does not claim that Nb8 is an engine principal variation, that an exact endgame result is verified when the evidence says it is not, or that a tool output replaces human calculation. The conclusion is limited to the recorded boundary and the exception the order of checks before captures.