Correspondence, blindfold, simultaneous exhibitions, consultation and odds do not all change the underlying move rules.
They instead alter one or more of:
time → information access → player relationship → starting resources → move transmission.
This area proves why variant, mode and format must remain separate concepts.
Correspondence Chess
Correspondence chess is a mode in which opponents transmit moves remotely and normally receive far longer reflection periods than OTB play. The underlying chess rules can remain orthodox or use a variant such as Chess960.
Remote Move Transmission
Moves can be transmitted by post, email or a dedicated server; transmission method is part of the mode, not the piece rules.
Postal History
Postal correspondence historically allowed games across cities/countries over months or years. The broader historical narrative belongs in chess history; here the relevant question is how remote move transmission changes the mode of play.
Server Correspondence
Modern server correspondence centralizes timestamps, move transmission, claims and tournament administration.
ICCF
The International Correspondence Chess Federation (ICCF) is the principal international governing body for official correspondence chess; current rules are versioned and event-specific.
Long Time Controls
Correspondence reflection time is measured on scales far longer than ordinary OTB controls and can include leave, time banks or server-specific counting rules.
Conditional Moves
A conditional move is a pre-submitted response sequence executed if the opponent follows the specified line; exact server/event support and commitment rules are source-specific.
Analysis Tool Rules Are Event-Specific
Engine, database, book and tablebase policies differ by correspondence authority/event. Never teach a universal engines allowed or engines forbidden rule.
Engines / Databases — Rule Provenance
Before using external analytical help, read the exact event regulations. ICCF, national federations and platform correspondence products can impose different assistance policies.
Adjudication / Tablebase Rules
Correspondence events can have special adjudication/tablebase claims. Current ICCF 2026 rules recognize certified 7-piece tablebase claims, illustrating why OTB draw assumptions cannot simply be copied across modes.
Correspondence Chess960
ICCF's 2026 rules include a World Correspondence Chess 960 Championship pathway, proving that variant and mode are orthogonal.
Variant + Mode Are Orthogonal
A game can simultaneously be Chess960 (ruleset) and correspondence (mode), or orthodox chess (ruleset) and blindfold (mode). Taxonomy should permit independent dimensions.
Blindfold Chess
Blindfold chess is ordinary chess played without visual access to the board/pieces, requiring the player to maintain the known position mentally.
Same Legal Game, No Visible Board
Blindfold normally changes information presentation, not legal state or hidden opponent information; all moves remain those of the underlying ruleset.
Board-State Memory
The player must reconstruct current occupancy, rights and side to move from memory of the move history.
Visualization
Blindfold performance depends heavily on visualization and accurate state updating; the underlying calculation skills are the same ones used in ordinary board visualization.
Blindfold vs Hidden Information
Blindfold hides the display from the player; Kriegspiel/Fog of War withholds objective game information by rule. The concepts are fundamentally different.
Blindfold Simultaneous Displays
A strong player can conduct multiple blindfold games at once; this combines blindfold mode with simultaneous-exhibition mode.
Accessibility Blind Mode Is a Different Concept
A screen-reader or accessibility blind mode can present full chess information nonvisually. It is an accessibility interface, not necessarily blindfold chess.
Simultaneous Exhibition
In a simul, one player faces many opponents on separate boards, normally cycling among them under declared move/clock procedure.
One Player vs Many Boards
The asymmetry is in player relationship and time allocation, not necessarily the underlying chess rules.
Move-Order / Clock Variants
Simuls can use different conventions for when challengers move and how clocks operate; event rules must specify them.
Simul Is a Mode
A simul can be orthodox, Chess960 or another ruleset. The multi-board exhibition structure is a mode.
Consultation Chess
Consultation chess assigns a side to a group that jointly chooses a single move.
Team Chooses One Move
The consultation group's internal discussion produces one legal move for the side; it is not Bughouse-style multiple boards/pockets.
Historical Consultation Games
Consultation matches were historically important public and club events; historical claims about particular matches should be checked against dated sources.
Hand-and-Brain / Cooperative Training Forms
Hand-and-Brain and similar community/training games divide decision responsibilities among partners. They are informal/cooperative modes whose exact rules vary.
Community-Specific Rules
Informal modes require an explicit rule card because names often describe a family rather than one standardized implementation.
Material Odds
Material odds remove or add starting material to handicap one side while leaving later movement rules largely orthodox.
Pawn Odds
Pawn odds begin with a specified pawn removed; which pawn and any compensating rule must be stated.
Move Odds
Move odds alter first-move privileges or grant extra opening moves; these can change legality/history and require exact definition.
Time Odds
Time odds use unequal clocks rather than changing board material; this is a handicap/competitive-mode parameter, not a piece-rule variant.
Starting-Position Handicap
A handicap can use a nonstandard but legal/declared starting position rather than simply removing one piece.
Classify Case by Case
Odds can modify board state, clock or move rights. Classify the changed dimension instead of forcing every handicap into variant.
Alternative-Forms Practice Set
A strong understanding includes distinguishing correspondence/blindfold/simul/consultation/odds by the dimension changed and checking tool/clock/community rules before play.
Mode Changes the Decision Environment
Correspondence chess can preserve ordinary piece legality while radically changing the analysis budget. Blindfold play changes the player's interface with the state. A simul changes attention allocation. Consultation changes who produces a move. Odds change starting resources.
That is why “same rules” does not mean “same skill demands.”
Correspondence Policies Must Be Versioned
External assistance is not defined by the word correspondence. Governing bodies, national organizations and platforms can adopt different policies for engines, databases, books, tablebases, conditional moves and claims. Record the authority, event and date.
For official ICCF play, current regulations are the relevant source; do not back-project OTB assumptions into server correspondence.
Blindfold, Hidden Information and Accessibility
Cognitive blindfold chess asks a player to maintain a fully determined public game state without seeing a board. Hidden-information variants intentionally withhold part of the state. Accessibility interfaces can also present a full state non-visually. These experiences may look similar from outside but demand different data and fairness models.
Odds Must Specify What Is Given
Material odds, move odds and time odds change different resources. A queen-odds game changes the initial material state; time odds change only the clock; move odds change initiative. Treat them as explicit handicap profiles rather than assuming the generic word odds defines a ruleset.