Nudge
A small change in how choices are presented that predictably shifts behavior without banning options or changing economic incentives.
What it means
A nudge is any aspect of the choice architecture that alters people's behavior in a predictable way without forbidding any options or significantly changing their economic incentives. The defining test is that a nudge must be easy and cheap to avoid — it steers rather than compels — which is what distinguishes it from a mandate, a ban, or a meaningful financial reward or penalty. Nudges exploit the predictable workings of intuitive (System 1) judgment, using defaults, salience, framing, social norms, and friction to make the better choice the path of least resistance. The concept is rooted in libertarian paternalism: the claim that it is legitimate to influence choices for people's own good while preserving their freedom to choose otherwise. Nudges have been criticized on grounds of effect size (many shift behavior only modestly), durability, transparency, and the worry that they can shade into manipulation or be reversed into 'sludge' that obstructs people. It matters because nudges offer low-cost, freedom-preserving alternatives to regulation, and because the same techniques can be used ethically or abusively depending on whose interest they serve.
Examples
Putting fruit at eye level in a cafeteria nudges healthier eating; nobody is stopped from reaching past it for the chips.
The etched fly in Schiphol airport's urinals gives men something to aim at, cutting spillage — no rule, no fine, just a target that makes the tidier option automatic.
A text reminding you of tomorrow's dentist appointment cuts no-shows; you are free to ignore it, and nothing about the cost of missing has changed.
First described in Thaler & Sunstein, 'Nudge' (2008).