Quick answer
Underpromotion Rules is a rules question: the legal-move test. Work from the first evidence position for Underpromotion Rules, and begin by testing e4.
Begin from e4 in 8/8/4k3/8/8/4P3/4K3/8 w - - 3 3. Read the side to move, legal conditions, history fields and procedural distinction before relying on a shortcut. The evidence answer is: Underpromotion Rules: identify checks, captures, pins and king safety before accepting a move as legal. Candidate line: e4.
In the Underpromotion Rules example, notice: side White; pieces Black king e6, White pawn e3, White king e2; legal first moves e4, Kd3, Kf3, Kf2, Kf1, Ke1, Kd1, Kd2. The side-to-move and piece list are scoped to this teaching position and stop there.
The exact condition
The first evidence board tests the legal-move test; the second board tests the legal-move test. A opens with the string direct FEN setup, whereas B opens with direct FEN setup. Look up neighbouring ideas via the Chess Wiki and the Rules hub. Then compare Piece Movement with Choosing A Promotion Piece, The Pawn Two Square Move, Chess Board Coordinate Notation around a malformed game record.
The two inventories make the distinction concrete. A contains side White; pieces Black king e6, White pawn e3, White king e2; legal first moves e4, Kd3, Kf3, Kf2, Kf1, Ke1, Kd1, Kd2; B contains side White; pieces Black king d8, White pawn e2, White king f2; legal first moves e3, e4, Ke3, Kf3, Kg3, Kg2, Kg1, Kf1. Compare the side to move before comparing the labels in the context of the identity used for repetition.
Topic dossier for this page and board pair r1:8 | r2:8 | r3:4k3 | r4:8 | r5:8 | r6:4P3 | r7:4K3 | r8:8 / r1:3k4 | r2:8 | r3:8 | r4:8 | r5:8 | r6:8 | r7:4PK2 | r8:8: start with a malformed game record; then test the identity used for repetition; keep the halfmove clock field separate from the history that changes a right; use whether a square is attacked as the transfer check; and reserve the exact side-to-move condition for the exception.
Procedure and counterexample
On the first board, calculate e4 after e4 and write down the opponent's best reply around a malformed game record. On the second board, calculate e4 after e4 and check the identity used for repetition. Separate what the board proves from what only the move record, clock or arbiter can establish. In this case the useful condition is the exact side-to-move condition.
Key claim: Underpromotion Rules is illustrated here by the legal-move test; the first concrete test is e4. The board anchor is 8/8/4k3/8/8/4P3/4K3/8; the example is intentionally narrower than the topic label and should not be generalised without checking the surrounding position..
Practical boundary: To answer “When is underpromotion rules legal, what exceptions matter, and how can a player verify the rule at the board?”, compare the recorded setup with e4 and the opponent's reply. The decision is useful only when the stated condition survives that concrete test on board 3k4/8/8/8/8/8/4PK2/8. The evidence records The position tests the stated rule or record field; verify the relevant source when a procedural decision matters and the second board signature r1:3k4 | r2:8 | r3:8 | r4:8 | r5:8 | r6:8 | r7:4PK2 | r8:8. The false-positive test is whether the halfmove clock field appears without the history that changes a right, so the conclusion is useful only when the stated condition survives that concrete test.
Evidence positions
example-1: the legal-move test
Show answer
Underpromotion Rules: identify checks, captures, pins and king safety before accepting a move as legal. Candidate line: e4.
Why this position is here: Underpromotion Rules is represented by the legal-move test. This is a direct FEN setup with board anchor 8/8/4k3/8/8/4P3/4K3/8; no opening history is inferred from the diagram.
FEN: 8/8/4k3/8/8/4P3/4K3/8 w - - 3 3
Question: What is the first concrete decision in this underpromotion rules position?
Answer cue: Underpromotion Rules: identify checks, captures, pins and king safety before accepting a move as legal. Candidate line: e4. The first candidate to test is e4. Replay e4 on board anchor 8/8/4k3/8/8/4P3/4K3/8 and write down what changes after it.
Evidence boundary: The position tests the stated rule or record field; verify the relevant source when a procedural decision matters.
example-2: the legal-move test
Show answer
Underpromotion Rules: identify checks, captures, pins and king safety before accepting a move as legal. Candidate line: e4.
Why this position is here: Underpromotion Rules is represented by the legal-move test. This is a direct FEN setup with board anchor 3k4/8/8/8/8/8/4PK2/8; no opening history is inferred from the diagram.
FEN: 3k4/8/8/8/8/8/4PK2/8 w - - 2 2
Question: What is the first concrete decision in this underpromotion rules position?
Answer cue: Underpromotion Rules: identify checks, captures, pins and king safety before accepting a move as legal. Candidate line: e4. The first candidate to test is e4. Replay e4 on board anchor 3k4/8/8/8/8/8/4PK2/8 and write down what changes after it.
Evidence boundary: The position tests the stated rule or record field; verify the relevant source when a procedural decision matters.
Reading the record
Read the first example (id example-1) as a complete record: continuation e4, source fide-laws. This is a direct FEN setup with board anchor 8/8/4k3/8/8/4P3/4K3/8; no opening history is inferred from the diagram. If A does not expose the legal-move test, correct the evidence before relying on the prose.
Read the second example (id example-2) separately: continuation e4, source fide-laws. Its feature is the legal-move test; inventory side White; pieces Black king d8, White pawn e2, White king f2; legal first moves e3, e4, Ke3, Kf3, Kg3, Kg2, Kg1, Kf1. Compare what changes between e4 and e4.
Common confusions
The main mistake to avoid with Underpromotion Rules is remembering a simplified slogan while overlooking a history field, exception or procedural condition. In A, the missing condition must be located in r1:8 | r2:8 | r3:4k3 | r4:8 | r5:8 | r6:4P3 | r7:4K3 | r8:8 after e4; in B, test it against r1:3k4 | r2:8 | r3:8 | r4:8 | r5:8 | r6:8 | r7:4PK2 | r8:8 after e4.
For Underpromotion Rules, the first board's evidence boundary (after e4) is The position tests the stated rule or record field; verify the relevant source when a procedural decision matters. The second board's evidence boundary for Underpromotion Rules is The position tests the stated rule or record field; verify the relevant source when a procedural decision matters. If a trusted source or careful calculation changes the conclusion around whether a square is attacked, update both the evidence record and this article.
Practice with a position
rebuild the position from the initial board, change one condition, and explain exactly which rule changes the result. Start with A's side to move and r1:8 | r2:8 | r3:4k3 | r4:8 | r5:8 | r6:4P3 | r7:4K3 | r8:8; record two candidates, the reply to e4 and the correction. Repeat with B's side to move and r1:3k4 | r2:8 | r3:8 | r4:8 | r5:8 | r6:8 | r7:4PK2 | r8:8; the changed board tests transfer rather than diagram memory.
After the drill, compare your notes with Choosing A Promotion Piece, The Pawn Two Square Move, Chess Board Coordinate Notation through the history that changes a right. Keep A's rejected alternative beside B's chosen line e4; this shows whether the conclusion survived a new board signature.
Sources and scope
Sources for Underpromotion Rules: FIDE Laws of Chess, 1chess.online editorial scope. Source ids are fide-laws, original-analysis. Primary evidence hook: fide-laws. Comparisons and practice notes are editorial. Evidence revision: 2026-08-remediation-r2.
Scope note for board pair r1:8 | r2:8 | r3:4k3 | r4:8 | r5:8 | r6:4P3 | r7:4K3 | r8:8 / r1:3k4 | r2:8 | r3:8 | r4:8 | r5:8 | r6:8 | r7:4PK2 | r8:8: this page does not claim that e4 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 halfmove clock field.