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 game decision procedure: players fix their initial current actions without first seeing the other players' current choices, those fixed actions are disclosed together, and the game applies rules to their combination. The selections need not be made at the same clock instant. What matters is the information boundary: no player may choose or revise that initial action in response to another's disclosed initial action before the common reveal.[1][2][3]
The means of fixing a choice vary. In Diplomacy, players write secret unit orders after negotiation and reveal them together. In Stack Attack, each player places a chosen card face-down, then all reveal. Under the WRPSA rock-paper-scissors rules, players form and show a gesture on the shared “Shoot” cue; a late throw made after seeing the opponent's hand is a foul. The gesture becomes fixed at disclosure. None of these sources makes an advance written commitment, silence before choice, universal fairness, faster play, or a particular conflict outcome part of the common mechanic.[1][3][2]
Structural Signature¶
Sig role-phrases: game participants; initial legal actions; protected current-choice information; common disclosure of fixed actions; joint rule-governed resolution.
- Game participants. At least two players take part in the same bounded decision episode. Diplomacy uses multiple powers, Stack Attack allows two to six players, and a WRPSA throw uses two. Without another current chooser whose selection is shielded, there is no simultaneous selection among players.[1][3][2]
- Initial legal actions. Each participant has a move to select for the episode: a unit order, a card from hand, or one of three legal gestures. The procedure concerns which available action is fixed, rather than the player's general strategy or the eventual game result.[1][3][2]
- Protected current-choice information. Other players' initial current selections are unavailable for a responsive selection of one's own before it is fixed. Secret written orders and face-down cards realize this by concealment; WRPSA realizes it by a common timing cue and a penalty for a late reactive throw. Prior-round information or pre-choice discussion may still be available.[1][3][2]
- Common disclosure of fixed actions. The initial selections enter shared play together, with no opportunity to revise those selections in response to the disclosure. Writing and face-down placement separate fixation from reveal. A valid gesture throw fixes and reveals its shape on the same cue. The rule does not ban every later decision during resolution.[1][3][2]
- Joint rule-governed resolution. The game's rules use the combination of selected actions. Diplomacy resolves the revealed orders in a subsequent phase; Stack Attack normally processes revealed cards from lowest to highest; WRPSA applies its beats relation or a matching-gesture replay. The Selection is simultaneous on the information axis even when adjudication takes time or proceeds in sequence.[1][3][2]
Remove the protected information or allow a player to change its initial selection after seeing another's, and the decision episode becomes sequential on that axis. Remove the rule that interprets the combination, and hidden private choices alone do not constitute this bounded game mechanic.
What It Is Not¶
It is not a mandatory secret-commitment device. A written order or face-down card is one way to fix a choice; a legal WRPSA gesture is formed and revealed on the same cue. Calling the closed fist during the countdown a prior choice of rock, paper, or scissors would misstate the rule.[2]
It is not an entire game turn occurring simultaneously. Stack Attack reveals selected cards together and then resolves them one at a time; its Switch card can require a later choice about swapping cards. That later resolution choice does not reopen the initial card selection. Diplomacy likewise separates negotiation, order writing, revelation, and resolution.[3][1]
It is not a guaranteed outcome property. These rulebooks do not establish that the procedure makes every game fair, fast, free of conflict, or free of every possible initiative advantage. It removes one specific opportunity: choosing an initial current action after seeing another initial current action. Other informational and rule asymmetries remain possible.[1][3][2]
Scope of Application¶
The entry covers a decision episode within a game, rather than a universal rule for a whole match. A publisher may call the episode a turn, as Stack Attack does within a multi-turn round, or separate it into writing and resolution phases, as Diplomacy does. A hand-game throw is shorter still. The common test is whether initial current actions stay unseen until fixation, enter shared play together, and are interpreted jointly by game rules.[1][3][2]
The directly inspected WRPSA and Stack Attack rules support unlike gesture and face-down-card implementations; publisher-indexed passages of the official Diplomacy rulebook support its written-order implementation. The evidence here does not establish that a sealed-bid auction is itself a case of this Game mechanic, though it may resemble a wider simultaneous-choice protocol. Nor does every board game that allows several people to think at once use this procedure: their current moves may still be taken in an observable sequence.
Clarity¶
The word simultaneous can refer to three different timings: private deliberation, disclosure of selected actions, and resolution of those actions. This entry assigns the label to the initial selection's information rule. In Stack Attack, players may think for different lengths of time, reveal selected cards together, and then apply them in numeric order. In WRPSA play, gesture formation and reveal coincide. Treating those differences as contradictions would obscure the one role that survives across cases.[3][2]
The distinction also clarifies what an observed “reaction” is. A late WRPSA throw selected after seeing the other hand breaches the procedure. A Stack Attack Switch effect chosen after the cards are revealed belongs to a later resolution step specified by that game's rules; it does not show that the initial card was chosen reactively. The analyst has to identify which choice was protected.[2][3]
Manages Complexity¶
A game phase can contain negotiation, private planning, a selection deadline, common disclosure, adjudication, and later options. Describing all of it as “simultaneous play” hides the ordering that matters. The five roles compress the phase into a smaller set of questions: who chooses, what initial action is legal, when can another current choice be seen, when does that initial choice close, and how do the combined actions affect play?
This compression keeps local details available when they matter. Diplomacy's written orders make pre-reveal fixation visible in a document; Stack Attack's face-down card does so physically; the WRPSA cue requires correct timing without a separate artifact. Stack Attack's sequential resolution and Switch effect show why an account of the selection protocol must not silently dictate the later adjudication protocol.[1][3][2]
Abstract Reasoning¶
To classify a candidate phase, first mark the initial action under test, not every action a player may make in the turn. Then locate each player's information set at the moment that initial action becomes fixed. If one player can inspect an opponent's already disclosed current action and still choose a response as its own initial action, the phase fails the simultaneous-selection test. If choices are fixed while hidden and enter shared play together, inspect the game rule that resolves their combination.[1][3][2]
This yields a useful counterfactual. Change only Stack Attack's selection rule so the second player may see the first face-up card before selecting its own card: the numeric placement rules could remain, but the initial action selection would become sequential. Conversely, retain the face-down common reveal but change the resolution order: the selection procedure persists while the game's downstream effects may change. The inference concerns procedure membership, not a prediction of how skilled players will perform.
Knowledge Transfer¶
The test transfers literally among game procedures with unlike carriers. Written unit orders, face-down cards, and timed gestures have different materials and different later resolution rules, yet each protects initial current choice until fixation and discloses the selected actions together. When adapting a game rule, one can preserve that information relation while changing the available actions or outcome table; those changes may alter strategy without changing the selection procedure.[1][3][2]
Outside games, a sealed bid or parallel vote may share a hidden-choice and common-disclosure skeleton. Those comparisons are analogies for this entry until the broader protocol is independently admitted and sourced. A cross-domain pattern should not be inferred merely because the same words “simultaneous” and “choice” occur elsewhere.
Examples¶
Canonical — Stack Attack card selection¶
In Tactus Studio's rules, each player selects one card from a private hand and places it face-down. All selected cards are revealed together. The game normally resolves those cards in ascending numeric order, finishing each card before proceeding. A Switch effect may later direct a swap after reveal, but the original selected cards have already been exposed.[3]
Mapped back: the participants are the card players; the initial legal actions are their card selections; protected information is the face-down choice; common disclosure reveals all selected cards together; joint resolution applies the cards under the placement and action rules. The later Switch decision shows the boundary of the initial-choice claim.[3]
Applied — a WRPSA rock-paper-scissors throw¶
Under WRPSA rules v1.0, two players keep closed fists through the count and form and reveal one of three legal gestures on “Shoot.” A throw delayed to respond to the opponent's visible hand is a foul. Rock beats scissors, scissors beats paper, paper beats rock, and identical gestures tie and are replayed.[2]
Mapped back: the two participants select initial legal actions from the three gestures; the cue and late-throw rule protect current-choice information; gesture formation and common disclosure coincide; the beats or tie rule supplies joint resolution. No written commitment is needed.[2]
Supporting — Diplomacy written orders¶
Publisher-indexed passages of the official rulebook say players negotiate, then secretly write unit orders; once all have written, they reveal the orders together and resolve them afterward. That source access supports the high-level role sequence, while full PDF pages and detailed adjudication rules were not directly inspected in this pass.[1]
Mapped back: the participants are the players, their initial actions are written unit orders, secrecy protects the current choices, the orders receive a common disclosure, and a subsequent phase supplies rule-governed resolution. Prior negotiation is compatible with the mechanic.[1]
Structural Tensions¶
The rulebooks support design distinctions, but not a universal pressure pair that every simultaneous-selection procedure must balance. Secret writing, face-down placement, and a shared throw cue all protect an initial action while imposing different timing and enforcement methods. Stack Attack shows that common reveal can coexist with sequential resolution and later local decisions; Diplomacy shows that conversation can precede protected choice. These are reasons to inspect the relevant phase, rather than generic promises or universal costs.[1][3][2]
One diagnostic matters in practice: which exact choice is protected from responsive revision, and at what event does that protection end? A proposed rule that permits a player to change its initial action after seeing the others has altered the mechanic; one that permits a later adjudication choice may not have. The present sources do not justify padding this section with claims about fairness, speed, or conflict rates.
Structural–Framed Character¶
The core information-and-timing test is structural: given a game's legal actions, one can inspect whether current selections are shielded through fixation and commonly disclosed. Its evaluative weight is separate: a designer may favor or dislike the resulting play, but the procedure's presence does not prove fairness or enjoyment. Its human-practice dependence lies in players following disclosure and anti-reaction rules; cards or documents can enforce some of the same relation materially.[1][3][2]
Its institutional origin is a game's constitutive rules, which define legal actions, cues, and resolution. Its vocabulary travel is literal across game genres when the same phase roles are present, and only a suggested analogy outside games. Its import-versus-recognition boundary is the enacted or specified information rule: merely naming a game “simultaneous” does not import protected selection if a player may still make an initial responsive move. The portable skeleton of concealed or unavailable current choices plus common disclosure is a future broader-pattern question; it does not by itself establish this game's outcome rule as a Prime.[1][3][2]
Its character: a structurally recognizable selection-and-disclosure procedure whose legal actions and consequences are framed by the rules of the particular game.
Structural Core vs. Domain Accent¶
The skeletal relation is fix initial choices without observing one another's current choices, then disclose them together. It appears with different physical carriers in the three sourced games. The domain accent is the set of legal game actions and the rule that interprets their combination as a round or phase result: unit orders, cards, and gestures do not share an outcome function.[1][3][2]
This entry does not yet clear the Prime bar. The source record establishes a reusable game mechanic, not a separately tested cross-domain simultaneous-choice identity. A sealed-bid auction might illustrate a broader protocol, but a metaphorical resemblance cannot substitute for a second admitted non-game member and its own evidence. The reviewed current catalog supplies no strict all-instance parent, so this entry is a provisional unparented root. The broader skeleton remains an explicit future-Prime question rather than an invented ancestor.
Instantiates / Related Primes¶
The live Decision Prime is a neighboring idea because each player selects an alternative, but its full uncertainty, trade-off and path-commitment signature is not established as a necessary constituent of every admitted episode. The initial-choice validity rule likewise does not establish the live Constraint Prime's full feasible-set and binding-versus-slack signature as an internal object. Commitment and Commitment Device are related only for implementations such as written orders or face-down cards, not for a gesture that becomes fixed at reveal. Mixed Strategy is a policy that assigns probabilities to actions; players can use this procedure while choosing deterministically. The live Rock Paper Scissors Prime captures the cyclic beats relation, not the timing rule; Diplomacy and Stack Attack instantiate this procedure without that cycle. These are semantic distinctions, not asserted DAG parents.
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¶
- An alternating responsive turn: if a player sees an opponent's current move before choosing its own initial action, the information rule differs even if both actions later feed one board state.
- An advance commitment artifact: writing orders and laying a card face-down are local implementations; the WRPSA gesture case does not require an earlier recorded choice.[1][3][2]
- A simultaneous outcome or adjudication: Stack Attack resolves exposed cards sequentially. Selection timing and resolution timing are separate axes.[3]
- A mixed strategy or payoff cycle: randomization and rock-paper-scissors's three-way beats relation concern strategy and payoff, respectively, rather than this disclosure procedure.
- A general auction or voting protocol: those may share a broader hidden-choice skeleton, but are outside this sourced game-mechanic entry.
References¶
[1] 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. registry ↩a ↩b ↩c ↩d ↩e ↩f ↩g ↩h ↩i ↩j ↩k ↩l ↩m ↩n ↩o ↩p ↩q ↩r ↩s ↩t
[2] 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. registry ↩a ↩b ↩c ↩d ↩e ↩f ↩g ↩h ↩i ↩j ↩k ↩l ↩m ↩n ↩o ↩p ↩q ↩r ↩s ↩t ↩u ↩v
[3] 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. registry ↩a ↩b ↩c ↩d ↩e ↩f ↩g ↩h ↩i ↩j ↩k ↩l ↩m ↩n ↩o ↩p ↩q ↩r ↩s ↩t ↩u ↩v ↩w