Nudge Wiki

Concept

Commitment Devices

self-control present-bias goal-pursuit

A commitment device removes a future choice in advance, binding a "future self" to a decision the "present self" might otherwise defer or abandon — named for Odysseus ordering his crew to lash him to the mast so he could hear the Sirens' song without acting on it. Owain Service frames the underlying problem as an ongoing conflict between a present self (who prefers ice cream and rest) and a future self (who prefers exercise and saving) — the present self, when the future arrives, simply becomes a new present self and defers again.

Public commitment amplifies the effect. A colleague at the Behavioural Insights Team, Rory, wrote "I will go to the gym twice a week for three months" on the team's shared office whiteboard — the public, visible pledge created a felt duty to remain consistent with it. Service argues wedding vows work the same way: Randy Olson's 2014 analysis found couples married in front of larger audiences divorce at markedly lower rates than couples who elope (see Randy Olson Wedding-Guest-Count Divorce Study), though Service flags likely confounding (couples marrying alone may be doing so more impulsively).

Writing a commitment down works even without an audience. A 1997 German study got students to write down exactly when and where they'd complete an unwanted Christmas Eve assignment; those who specified a plan were more than twice as likely to complete it (see German Christmas Eve Assignment Commitment Study) — an early implementation-intention finding. The same logic reduced conformity in a modified version of Solomon Asch's line-length study: asking participants to write down their answer before anyone else spoke cut group-pressure errors by more than three-quarters (see Asch Line-Length Conformity Study). Katie Milkman's own vaccination-uptake research found writing down a specific date and time raised flu-shot uptake by 13% among 3,300 employees (see Milkman Vaccination Write-Down-Date Study) — distinct from her separately-documented "reserved for you" framing study (see Milkman Duckworth Patel Flu-Vaccine Reservation Study).

A field-tested BIT commitment contract. A UK Jobcentre Plus trial (Essex) had job seekers pledge specific actions (CV work, applications) ahead of their next advisor meeting; treatment-group job seekers were 15-20% more likely to be off benefits and working 13 weeks later (see BIT Essex Jobcentre Commitment Contract Study).

Choosing in advance shifts preference toward the "better" option. A 1999 study found students choosing which film to watch that same night chose lowbrow films (Happy Gilmore 2 over Hamnet), but the same students choosing a week in advance were 37% more likely to pick highbrow films — the same effect Service claims generalizes to snack choices for a future meeting (see Reed Loewenstein Kalyanaraman Highbrow-Lowbrow Movie Study).

A binding savings-account field experiment. Nava Ashraf, Dean Karlan, and Wesley Yin's "Tying Odysseus to the Mast" study offered Philippine bank customers an otherwise-identical savings account that locked funds until a self-set goal was reached; about 30% chose the binding account despite the restriction, and after 12 months this group's savings balances rose 81% more than a control group (see Ashraf Karlan Yin Philippines Commitment Savings Study).

Bright-lines thinking (Episode 293). Service and Gallagher advocate categorical, binary rules over graduated targets — "don't drink two days a week" rather than "drink under X units," modeled on religious rules like not working on the Sabbath — because a clean binary line is cognitively easier to track and adhere to than a number that requires ongoing counting.

Discussed in

  • Episode 291 — 291-why-willpower-alone-doesn-t-work
  • Episode 293 — 293-how-peer-pressure-built-a-5-billion-fitness-revolution (bright-lines thinking)

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