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Sequential vs. Simultaneous Move Recognition

Why It Matters

The same payoff structure produces completely different outcomes depending on move timing. Sequential play enables commitment (first-mover locks in a strategy that constrains others), incredible threats become incredible (you can observe whether threats will actually be executed), and backward induction allows solving by working backward from end states. Simultaneous play requires predicting opponent actions without observation, making commitment impossible and requiring equilibrium thinking. Misidentifying timing structure leads to wrong predictions and wrong strategies.

The Key Move

For any strategic interaction:

  1. Ask: when you choose your action, do you know what action(s) the other player(s) have chosen?
  2. If yes to any, it's sequential (at least partially).
  3. If no to all, it's simultaneous.
  4. For sequential games, map the decision tree showing who moves when.
  5. Apply backward induction: start from the final decision nodes, determine optimal choices, work backward to find the optimal strategy at each stage.
  6. For simultaneous games, use equilibrium analysis: find action combinations where no one wants to deviate.
  7. Check whether converting between simultaneous and sequential changes the outcome - if yes, timing structure is strategically important.

Classic Application

Entry deterrence in markets. Incumbent firm chooses capacity expansion before entrant decides whether to enter. If simultaneous: both firms would choose actions based on predicted responses, likely resulting in entry. If sequential (reality): incumbent expands capacity first, raising entrant's expected losses from entry. Entrant observes expansion and chooses not to enter. The key: expansion is a credible commitment (already built, sunk cost) that changes the entrant's optimization problem. Incumbent's first-mover advantage makes entry deterrence possible.

Surprising Application

Conflict resolution in relationships. Simultaneous structure: both partners simultaneously decide whether to escalate or de-escalate during an argument. Each fears that de-escalating while the other escalates means losing face, so both escalate (defection equilibrium). Sequential structure: one person explicitly de-escalates first, creating observable commitment. The other can then respond to observed de-escalation rather than predicted behavior. This explains why "I'll go first" statements work - they convert simultaneous (unstable, both escalate) to sequential (stable, both de-escalate) by introducing observation and commitment. Non-obvious because conversations feel simultaneous but sequential framing enables coordination.

Failure Modes

Ignoring information structure - just because moves happen at different times doesn't mean it's sequential (if later mover doesn't observe earlier move, it's effectively simultaneous). Assuming commitment is automatic - sequential advantage requires credible commitment (sunk costs, binding contracts). Backward induction with irrational players - assumes perfect rationality at every stage. Missing simultaneous components in sequential games - many games have both elements. Not checking for subgame perfection - equilibria in sequential games must be optimal at every decision node, not just overall.

Go Deeper

Dixit & Nalebuff, The Art of Strategy, Chapter 3; Gibbons, Game Theory for Applied Economists, Chapter 2.1