Pawn movement and promotion

Canonical source: docs/rules/pawn-vectors.md. This page is copied from the repository at build time; edit the repository file, not this page.

The tables give legal and illegal moves for ordinary and advanced central pawns in each army, using minimal custom positions. [official] identifies an outcome shown or stated by the official sources below; [inference] identifies a documented library interpretation where those sources do not spell out every orientation. The official tutorial determines pawn direction.

Sources

Source	URL	Role
Official illustrated quick rules (PDF)	https://play.quaternity.com/static/media/quick_start_rules.ee41e5de.pdf	Basic rules 1–17 (rules 3, 6, 9, 10 are pawn rules)
Official tutorial, quick start chapter 5	https://play.quaternity.com/how-to-play/quick-start/chapter5	Six ordinary pawns per army and their forward moves
Official tutorial, quick start chapter 6	https://play.quaternity.com/how-to-play/quick-start/chapter6	One-square forward move on the same file or rank
Official tutorial, quick start chapter 7	https://play.quaternity.com/how-to-play/quick-start/chapter7	Diagonal capture “in the direction of movement”
Official tutorial, quick start chapter 8	https://play.quaternity.com/how-to-play/quick-start/chapter8	Advanced central pawns; rank-or-file first move
Official tutorial, quick start chapter 9	https://play.quaternity.com/how-to-play/quick-start/chapter9	Advanced pawn “3 options for an attack”
Official tutorial, quick start chapter 10	https://play.quaternity.com/how-to-play/quick-start/chapter10	Commitment to the moved rank/file
Official tutorial, quick start chapter 11	https://play.quaternity.com/how-to-play/quick-start/chapter11	Main-diagonal capture keeps the choice open
Official tutorial, quick start chapter 12	https://play.quaternity.com/how-to-play/quick-start/chapter12	Promotion on the furthest rank/file, same move, same sq.
Opening position fixture	docs/fixtures/opening-position.md	The 64 starting squares and army corners

The tutorial is a public single-page app. Its per-chapter rule-illustration data (the selected pawn, the arrowDirection move arrows and the xMark attack squares) was read as the chapter’s pictured content — the same tutorial-data method used to check the starting position. No vendor engine or move-generation code was copied.

Official rule text quoted verbatim:

• Chapter 5: “Each player has six pawns, three of which are located on a rank and three on a file. Any pawn can be moved to the nearest square including the first move.”
• Chapter 6: “Pawns may move to the unoccupied square immediately in front of it on the same file or rank.”
• Chapter 7: “A pawn may also take opponent’s piece, located diagonally in the direction of movement of the pawn.”
• Chapter 8: “Each player has two advanced central pawns located on the main diagonal. Advanced central pawns may move on the rank or file depending on which direction they made their first move.”
• Chapter 9: “Each advanced central pawn has 3 options for an attack.”
• Chapter 10: “Once advanced central pawns move they are committed to the direction they were moved.” (10-2: first move horizontally → committed to the rank; 10-3: first move vertically → committed to the file.)
• Chapter 11: “If an advanced central pawn captures an opposing piece toward the center then it maintains the option on two directions.” (11-2: White advanced central pawn captured the green knight on e5; it stays an advanced pawn.)
• Chapter 12: “When a pawn reaches the rank/file furthest from its starting position it must be exchanged as part of the same move on the same square for a new queen, rook, bishop or knight of the same color.”
• PDF rule 3: “Pawns may move one square only per turn - even on their first move.”
• PDF rule 6: promotion as part of the same move on the same square; the choice is not restricted by previously captured pieces.
• PDF rule 9: the two Advanced Central Pawns “can choose to move left or right for their first move, after that … committed to the chosen direction.”
• PDF rule 10: an Advanced Central Pawn capturing on the main diagonal keeps the power to choose its subsequent direction until committing.

1. Orientation grounding (validated)

Each army’s pawns move perpendicular to the line they stand on, away from their own corner: pawns on a rank move along a file; pawns on a file move along a rank. [official] (chapters 5–6 picture every one of the six ordinary pawns and its arrow.)

Army (corner)	Rank-line pawns	Forward (file axis)	File-line pawns	Forward (rank axis)
White (bottom-l)	a5, b5, c5 (rank 5)	+rank (up): c5→c6	e1, e2, e3 (file e)	+file (right): e3→f3
Red (top-left)	a8, b8, c8 (rank 8)	-rank (down): c8→c7	e10, e11, e12 (file e)	+file (right): e10→f10
Black (top-right)	j8, k8, l8 (rank 8)	-rank (down): j8→j7	h10, h11, h12 (file h)	-file (left): h10→g10
Green (bottom-r)	j5, k5, l5 (rank 5)	+rank (up): j5→j6	h1, h2, h3 (file h)	-file (left): h3→g3

The two advanced central pawns per army sit on the army’s main diagonal (White and Black on a1–l12; Red and Green on a12–l1).

2. Ordinary pawns: forward move

Baseline setup for every row (see §7): White king a1, Red king a12, Black king l12, Green king l1; plus the pawn under test on its opening square and nothing else. [official] chapters 5–6.

Army	Pawn line	Pawn	Legal forward	Illegal (wrong axis)	Illegal (backward)	Illegal (blocked)
White	rank 5	c5	c5–c6	c5–d5, c5–b5	c5–c4	c5–c6 if c6 occupied
White	file e	e3	e3–f3	e3–e4, e3–e2	e3–d3	e3–f3 if f3 occupied
Red	rank 8	c8	c8–c7	c8–d8, c8–b8	c8–c9	c8–c7 if c7 occupied
Red	file e	e10	e10–f10	e10–e9, e10–e11	e10–d10	e10–f10 if f10 occ.
Black	rank 8	j8	j8–j7	j8–i8, j8–k8	j8–j9	j8–j7 if j7 occupied
Black	file h	h10	h10–g10	h10–h9, h10–h11	h10–i10	h10–g10 if g10 occ.
Green	rank 5	j5	j5–j6	j5–i5, j5–k5	j5–j4	j5–j6 if j6 occupied
Green	file h	h3	h3–g3	h3–h4, h3–h2	h3–i3	h3–g3 if g3 occupied

“Wrong axis” is the move a chess-trained reader expects: a rank-line pawn sliding along its rank (c5–d5, c5–b5), or a file-line pawn sliding along its file (e3–e4, e3–e2). “Backward” is the opposite direction along the pawn’s own movement axis (c5–c4 for the rank-line pawn, e3–d3 for the file-line pawn). Both are illegal here — the pawn moves perpendicular to its line and only forward.

3. Ordinary pawns: capture

A pawn captures on the two diagonals forward of its movement axis, one square each. [official] text (chapter 7) plus the chapter-7 pictures; the “two diagonals” reading is [inference] for the diagonal that chapter 7 does not picture (each chapter-7 example places only one enemy on a diagonal). This both diagonals are supported by this library (§8).

Baseline setup: §2, plus an enemy piece (“target”) on each named capture square. Capture squares are empty in the base case; × marks a capture.

Army	Pawn (axis)	Forward diagonals	Legal captures	Illegal (straight)	Illegal (backward diag.)
White	c5 (up)	b6, d6	c5×b6, c5×d6	c5×c6	c5×b4, c5×d4
White	e3 (right)	f4, f2	e3×f4, e3×f2	e3×f3	e3×d4, e3×d2
Red	c8 (down)	b7, d7	c8×b7, c8×d7	c8×c7	c8×b9, c8×d9
Red	e10 (right)	f11, f9	e10×f11, e10×f9	e10×f10	e10×d11, e10×d9
Black	j8 (down)	i7, k7	j8×i7, j8×k7	j8×j7	j8×i9, j8×k9
Black	h10 (left)	g11, g9	h10×g11, h10×g9	h10×g10	h10×i11, h10×i9
Green	j5 (up)	i6, k6	j5×i6, j5×k6	j5×j6	j5×i4, j5×k4
Green	h3 (left)	g4, g2	h3×g4, h3×g2	h3×g3	h3×i4, h3×i2

Chapter-7 anchors (each [official]): White e3×f4 (Red bishop), Red c8×b7 (White knight), Red e10×f11; the same chapter also shows Black g10×f11, Green j6×k7 and White c6×b7 on its custom lesson board. Every pictured capture is one of the two forward diagonals of the pawn’s axis, consistent with the table above.

4. Advanced central pawns: first-move commitment axes

An uncommitted advanced pawn moves one square along its rank or its file (forward only). [official] chapters 8–10. The first such move commits it to that rank (horizontal) or file (vertical) for the rest of the game.

Baseline setup: §2, plus the advanced pawn under test on its opening square.

Army	Pawn	File-axis move (commit file)	Rank-axis move (commit rank)	Illegal (backward)
White	d4	d4–d5 → file d	d4–e4 → rank 4	d4–d3, d4–c4, d4–c3
White	e5	e5–e6 → file e	e5–f5 → rank 5	e5–e4, e5–d5, e5–d4
Red	d9	d9–d8 → file d	d9–e9 → rank 9	d9–d10, d9–c9, d9–c10
Red	e8	e8–e7 → file e	e8–f8 → rank 8	e8–e9, e8–d8, e8–d9
Black	i9	i9–i8 → file i	i9–h9 → rank 9	i9–i10, i9–j9, i9–j10
Black	h8	h8–h7 → file h	h8–g8 → rank 8	h8–h9, h8–i8, h8–i9
Green	h5	h5–h6 → file h	h5–g5 → rank 5	h5–h4, h5–i5, h5–i4
Green	i4	i4–i5 → file i	i4–h4 → rank 4	i4–i3, i4–j4, i4–j3

After commitment the pawn is an ordinary pawn on that axis: e.g. after d4–d5 (commits file d) the only forward moves are d5–d6, d6–d7, … ; d5–e5, d5–c5 and d5–d4 are illegal. [official] chapter 10. An advanced pawn’s forward move — before and after commitment — is to the unoccupied square immediately in front of it on its chosen rank/file; a blocked forward square cannot be entered, exactly as for ordinary pawns (chapter 6). [official] A diagonal move is never a plain move — only a capture (§5).

5. Advanced central pawns: captures and the non-committing main-diagonal capture

Before commitment an advanced pawn may capture on three diagonal squares: the forward diagonal along its main diagonal (toward the center) plus the two side diagonals. [official] chapter 9 (“3 options for an attack”; White e5 pictures attack marks on d6, f6, f4). The per-army sets for Red, Black and Green are [inference] by symmetry — chapter 9 pictures only White’s e5 set, and chapter 11 pictures only White’s d4 set.

Army	Pawn	Capture set (3 squares)	Non-committing (toward center)	Committing side captures (committed direction)
White	d4	c5, e3, e5	d4×e5	d4×c5 (up), d4×e3 (right)
White	e5	d6, f4, f6	e5×f6	e5×d6 (up), e5×f4 (right)
Red	d9	c8, e8, e10	d9×e8	d9×c8 (down), d9×e10 (right)
Red	e8	d7, f7, f9	e8×f7	e8×d7 (down), e8×f9 (right)
Black	i9	h8, h10, j8	i9×h8	i9×h10 (left), i9×j8 (down)
Black	h8	g7, g9, i7	h8×g7	h8×g9 (left), h8×i7 (down)
Green	i4	h3, h5, j5	i4×h5	i4×h3 (left), i4×j5 (up)
Green	h5	g4, g6, i6	h5×g6	h5×g4 (left), h5×i6 (up)

Chapter 11 main-diagonal example [official]. Minimal setup: the four kings (§7) plus White pawn d4 and a Green knight on e5 (the chapter-11 lesson board). White plays d4×e5, capturing the knight toward the center. The pawn stays an advanced central pawn and keeps its choice of direction; it does not become committed. It now stands on e5 with the three attack squares d6, f6, f4 (chapter 9 / chapter 11 step 2). By contrast, capturing a side square (d4×c5 or d4×e3) is [inference] to commit the pawn to a persistent direction relative to its current square (§8): d4×c5 commits up from c5, so the pawn then moves c5–c6 and captures b6/d6; d4×e3 commits right from e3, so it then moves e3–f3 and captures f4/f2. The pawn does not stay on the original file/rank: old-line continuations are illegal (after d4×c5, c5–d5, c5–b5, c5–c4 and c5×d4 are illegal; after d4×e3, e3–e4, e3–e2, e3–d3 and e3×d4 are illegal). The same holds for White’s other advanced pawn: e5×d6 commits up from d6, and e5×f4 commits right from f4.

Illegal for an uncommitted advanced pawn: a diagonal move onto an empty square (e.g. d4–c5 with c5 empty); any backward straight move (§4); a capture on the square that points back toward its own corner (d4×c3, e5×d4).

6. Promotion

[official] chapter 12 and PDF rule 6.

• A pawn must be promoted when it reaches the rank/file furthest from its starting line — the board edge it is heading toward. It is mandatory, happens as part of the same move on the same square, and is not a separate turn.
• The choice is queen, rook, bishop or knight of the same colour — never a king or a pawn. The choice is unrestricted by previously captured pieces.

Army	Axis	Promotion edge	Example
White	up (+rank)	rank 12	chapter 12: d11–d12 becomes a queen
White	right (+file)	file l	e.g. k3–l3 promotes on l3
Red	down (-rank)	rank 1	e.g. c2–c1 promotes on c1
Red	right (+file)	file l	e.g. k10–l10 promotes on l10
Black	down (-rank)	rank 1	e.g. j2–j1 promotes on j1
Black	left (-file)	file a	e.g. b10–a10 promotes on a10
Green	up (+rank)	rank 12	e.g. j11–j12 promotes on j12
Green	left (-file)	file a	e.g. b3–a3 promotes on a3

An advanced pawn promotes on the edge of its committed direction: a pawn committed up (e.g. d4–d5…d11–d12) promotes on the far rank (d12); a pawn committed right (d4–e4…k4–l4) promotes on the far file (l4); after a side capture the direction is preserved relative to the new square (§5), so d4×c5 then up c5–c6…c12 promotes on rank 12 and d4×e3 then right e3–f3…l3 promotes on file l. [inference] for the advanced-pawn paths; the ordinary case is [official].

Promotion and check (baseline caution). With the §7 default home corners (Red king a12, Black king l12), any White queen or rook promoting on rank 12 — the quiet d11–d12 or a capture such as d11×e12 — attacks along rank 12 and therefore gives check to both Red a12 and Black l12. The promotion rule itself is [official] and mandatory; only the check/mate consequences are separate adjudication questions. The example below uses a custom baseline so that promotion is the only thing under test.

Capture-to-promotion. [official] chapter 12 (same move, same square) with the §3 capture rule. Custom minimal setup, distinct from the §7 default corners: White king a1, Green king l1, Red king a10, Black king l10; plus a White advanced pawn on d11 committed up (forward move d11–d12) and a Red knight on e12. All four kings are safe before the move (the pawn d11 attacks only c12/e12; the knight e12 attacks only c11, d10, f10, g11) and after every promotion choice: a queen or rook on e12 attacks rank 12 and file e but no king stands there, a bishop on e12 attacks its a8/l5 diagonals, and a knight on e12 attacks c11, d10, f10, g11 — none is a king square. So d11×e12 is a legal forward-diagonal capture that lands on rank 12, and promotion is mandatory as part of that same move on e12: White must replace the pawn there with a queen, rook, bishop or knight of the same army/colour (White) — never a king or pawn, whichever of the four is chosen.

Blocked promotion edge. [official] chapter 6. With any piece occupying d12, the quiet move d11–d12 is illegal: the forward square is occupied and cannot be entered, so the pawn cannot promote by a straight move into an occupied edge square. Promotion only happens on a square the pawn can actually reach.

7. Minimal setups

• Kings baseline. White king a1, Red king a12, Black king l12, Green king l1. These four home squares are pairwise non-adjacent and no test piece below attacks them before the move under test, so all four kings are safe when the move begins; a case whose own move attacks a king is re-checked in §6.
• Custom baselines. Where a fixture needs the kings clear of a promotion rank — e.g. the §6 capture-to-promotion case — it states its own king squares and re-checks king safety; such cases are marked custom and do not use the default corners.
• Move cases use the baseline plus the single pawn under test on its opening square. Blocked cases additionally put any one piece on the forward square.
• Capture cases use the baseline plus the pawn under test and one enemy “target” piece on the capture square named in the row. Captures of an empty square are not captures.
• Advanced-pawn cases use the baseline plus the advanced pawn under test; the chapter-11 case adds a Green knight on e5.

All squares named are on the 12×12 board (a–l × 1–12).

8. Library interpretations

The official sources show the one-square forward move, captures, central-pawn commitment and promotion. The following details apply consistently across all four rotated armies; where a source does not picture every case, they are labelled [inference] rather than presented as a quotation.

Captures, commitment and promotion

1. Ordinary pawns capture on both forward diagonals. Chapter 7 states the generic rule (“located diagonally in the direction of movement”) and its alternate lesson examples each show one of the two forward diagonals (White e3×f4, White c6×b7, Red c8×b7, Red e10×f11, Black g10×f11, Green j6×k7); no example places enemies on both, but none excludes the second diagonal either. Both diagonals are therefore legal captures (§3).
2. A side capture commits the pawn to a persistent direction relative to its current square. For an uncommitted advanced pawn, a capture whose displacement fits exactly one forward direction commits it to that direction, applied from the square it now occupies — not to the original file/rank: White d4×c5 (left+up) commits up from c5 (c5–c6, captures b6/d6), White d4×e3 (right+down) commits right from e3 (e3–f3, captures f4/f2), White e5×d6 commits up from d6, White e5×f4 commits right from f4; the same rotation gives the Red, Black and Green side captures in §5. Old-line continuations are illegal (after d4×c5: c5–d5, c5–b5, c5–c4, c5×d4; after d4×e3: e3–e4, e3–e2, e3–d3, e3×d4).
3. The main-diagonal (toward-center) capture does not commit. White d4×e5 (right+up) fits both directions, so it stays uncommitted — the chapter-11 case. [official] chapter 11.
4. Red/Black/Green advanced attack sets rotate White’s shapes by each army’s corner and forward directions (§5); chapter 9 pictures only White’s e5 set.
5. A committed advanced pawn promotes on the boundary of its preserved direction (§6): a pawn committed up promotes on the far rank (e.g. d4×c5 then c5–c6…c12 promotes on rank 12), a pawn committed right promotes on the far file (e.g. d4×e3 then e3–f3…l3 promotes on file l).
6. An uncommitted pawn that reaches the far board edge by successive toward-center captures also promotes on entering the edge. Walking the main diagonal by repeated center captures (e.g. White d4×e5, e5×f6, f6×g7, …) reaches the far edge (White rank 12); chapter 12 makes promotion mandatory on reaching that rank/file, regardless of commitment.

Chapter 7’s generic diagonal wording and pictured captures support the two forward diagonals; chapter 10 describes direction commitment; chapter 11 keeps the choice open after a capture toward the centre; chapter 12 requires promotion at the far edge. The side-capture commitment and symmetry-derived cases remain labelled [inference]. The §1 orientation table and §2–§3 move examples follow the tutorial’s pictured directions, not ordinary two-player chess vectors.