Simultaneous action selection¶
A game decision procedure in which players fix current actions without seeing one another's choices, disclose them together, and resolve their combination under game rules.
Core Idea¶
Simultaneous action selection is a way to run one game decision episode. Players fix their initial current actions without seeing one another's current choices, disclose those fixed actions together, and apply game rules to the combination. The actions do not have to be chosen at the same instant. They do have to be protected from a player waiting to see another's disclosed current choice and then changing its own initial action.[ref-894da6cb7380][ref-acaf400bddae]
The protection can take different forms. Stack Attack players put chosen cards face-down before a shared reveal. In rock-paper-scissors under WRPSA rules, players form and reveal gestures on the “Shoot” cue; a late throw made after seeing the other hand is a foul. Secret written orders in Diplomacy provide another high-level case, supported here by indexed passages of the publisher's rulebook. None of these cases requires every implementation to use writing or a separate commitment device.[ref-acaf400bddae][ref-894da6cb7380][^ref-f8a2f592b284]
Use Within the Domain¶
This method applies to a decision phase inside a game, which a particular rulebook may call a turn, round, or part of a turn. Stack Attack calls each face-down card choice and reveal a turn within a longer round. The WRPSA hand-game example is one throw. Diplomacy separates negotiation, order writing, reveal, and later resolution. The shared identity is the information rule for initial choices, not a fixed duration for the whole game.[ref-acaf400bddae][ref-894da6cb7380][^ref-f8a2f592b284]
The method does not promise a fairer or faster game, guarantee conflict, or eliminate every possible initiative advantage. It specifically prevents a player from selecting its initial current action in response to another already revealed initial action. The outcome still depends on each game's own resolution rules.
Clarity¶
Three things can happen at different times: thinking about an action, revealing the selected action, and resolving the result. In Stack Attack, players may deliberate privately, reveal cards together, then resolve cards in number order. In WRPSA play, forming and showing a legal gesture happen together on Shoot. Both count as simultaneous action selection because the other current choice is unavailable for a valid responsive initial selection.[ref-acaf400bddae][ref-894da6cb7380]
A later decision need not break the earlier procedure. Stack Attack's Switch card can require a post-reveal swap choice during resolution. That choice does not let a player replace the card it initially selected face-down. Ask which particular choice was meant to be simultaneous.[^ref-acaf400bddae]
Manages Complexity¶
A busy game turn may contain talking, planning, secret choice, reveal, scoring, and later effects. The procedure gives a short checklist: who chooses, what initial action each can choose, when other current choices become visible, when those choices are fixed, and how the game resolves them. This separates the selection rule from a game's many other rules.
Written orders, face-down cards, and a common hand cue use different materials to serve the same information boundary. The later outcome rules can differ even when the selection method matches: Stack Attack processes cards sequentially, while WRPSA applies the rock-paper-scissors beats or tie rule.[ref-f8a2f592b284][ref-acaf400bddae][^ref-894da6cb7380]
Abstract Reasoning¶
To test a game phase, identify each player's initial current action. Then ask whether a player can see another player's disclosed initial action before fixing its own. If so, it can make an informed response and the initial action selection is sequential on that axis. If the choices are protected through fixation and disclosed together, inspect the rule that applies their combination.[ref-acaf400bddae][ref-894da6cb7380]
Imagine changing only Stack Attack so one player's selected card is shown before the next player chooses. The card-placement rule could stay the same, but the selection procedure would change. Alternatively, keep the face-down common reveal and change the order in which exposed cards are resolved: the selection procedure remains. This counterfactual helps locate which rule is responsible for which feature of play.
Knowledge Transfer¶
The same test works for a card selection turn and a timed gesture throw, despite different actions and outcomes. It also explains the high-level written-order pattern in Diplomacy. What transfers is protection of initial current choices until fixation plus their shared disclosure, followed by a rule that handles the combination. No source here proves a wider non-game identity for auctions or votes; those need separate review.[ref-acaf400bddae][ref-894da6cb7380][^ref-f8a2f592b284]
The existing catalog's Rock Paper Scissors entry describes a cyclic beats relation, not this timing procedure. Mixed Strategy describes randomizing among actions; players can select deterministically under simultaneous action selection. A commitment device may help in one implementation but is not needed for a gesture throw. The reviewed graph currently has no strict parent for this procedure, so it is provisionally unparented while any broader protocol identity remains a future question.
Example¶
In Stack Attack, each player secretly chooses a card from hand and places it face-down. Everyone reveals their selected card together. The cards are then normally resolved from lowest to highest, one at a time. The game's later Switch effect may change cards during resolution, but the initial selection has already been made and revealed.[^ref-acaf400bddae]
Mapped back: the card players are the participants; their selected cards are the initial legal actions; face-down placement protects current-choice information; turning the cards up together is common disclosure; the placement and action rules supply joint resolution. A round can contain several such turns.[^ref-acaf400bddae]
Neighborhood in Abstraction Space¶
Simultaneous action selection sits in a crowded region of the domain-specific corpus (38th percentile for distinctiveness): several abstractions share nearly its structure, so a description that fits it tends to fit its neighbors too.
Family — Strategic Games & Equilibrium Concepts (14 abstractions)
Nearest neighbors
- Game balance — 0.89
- Game — 0.88
- Cognitive Hierarchy Theory — 0.87
- Zugzwang — 0.87
- Rubinstein bargaining model — 0.87
Computed from structural-signature embeddings · 2026-10-17
Not to Be Confused With¶
- Alternating responsive turns: seeing another's current action before choosing one's own initial action changes the information rule.
- Advance written commitment: WRPSA gestures are fixed and revealed on the same cue; writing is optional across the documented cases.[^ref-894da6cb7380]
- Simultaneous resolution: Stack Attack reveals choices together and then processes cards in sequence.[^ref-acaf400bddae]
- A guarantee of fairness or speed: neither follows from the shared procedure alone.
- A sealed-bid auction: it may resemble a broader hidden-choice protocol, but this entry is a sourced game decision procedure.
References¶
[^ref-f8a2f592b284]: Hasbro / Avalon Hill, Diplomacy, The Game of International Intrigue, official 24-page rulebook; its printed title uses a colon after Diplomacy. How to Play overview and Order Writing Phase. Publisher-domain search-indexed original passages were inspected and independently matched against a separate Wizards of the Coast publisher-domain PDF excerpt; the full PDF and printed page numbers could not be directly verified here. Supports prior negotiation, secret order writing, common reveal and subsequent order resolution only. [^ref-894da6cb7380]: World Rock Paper Scissors Association, Official Rock Paper Scissors Rules, v1.0 (2026 edition), published 2026-07-20, web page updated 2026-09-27, Throw Mechanics, Round Resolution, and Fouls and Penalties. Full official HTML inspected 2026-10-08; supports the shared Shoot cue, late-throw foul and beats/tie outcome. Current web text may change; v1.0 is the consulted ruleset. [^ref-acaf400bddae]: Tactus Studio, Stack Attack, Rules, official full HTML rules; the displayed page title uses an em dash before Rules. §3 Setup, §4 Playing a Turn, §8 Action Cards, and §10 End of a Turn, inspected 2026-10-08. Supports secret face-down selection, common reveal, normal numeric sequential resolution, later Switch choice, and repeated choose/reveal cycles. Page has no numbered edition and may change.