Joseph Overton was a vice-president of the Mackinac Center for Public Policy, a free-market think tank in Michigan. In the mid-1990s he sketched a model to explain to donors why the Center funded research on policies that no legislator would touch. He died in a plane crash in 2003, and colleagues formalized the model afterwards and named it for him.
The idea is that at any moment, on any issue, only a narrow band of positions is politically viable. Overton's original ranking ran from unthinkable through radical, acceptable, sensible, popular, to policy. A politician cannot generally move the window; a politician can only operate inside it, because proposing something outside it is career-ending. What moves the window is everything else — advocacy, media, think tanks, activists, and the sustained public articulation of positions currently outside it.
Which yields a strategy that is now widely understood and widely used: the function of advocating an extreme position is not to enact it. It is to relocate the boundary, so that a position formerly considered radical becomes the moderate compromise.
Two established mechanisms explain why this works.
The first is anchoring, in the sense of chapter 14. A publicly stated extreme becomes a reference point against which other positions are measured, and adjustment from a reference point is insufficient. The midpoint between two positions moves when one of them moves, and the midpoint is where compromise lands.
The second is Muzafer Sherif's social judgment theory, which is more specific and more useful here. Sherif proposed that people evaluate a message against their own position, and that around that position lie three regions: a latitude of acceptance, a latitude of non-commitment, and a latitude of rejection. A message inside the latitude of acceptance is assimilated — perceived as closer to your own view than it is. A message inside the latitude of rejection is contrasted — perceived as further away than it is, and rejected more strongly than its content warrants.
The strategic consequence is that persuasion has a maximum step size. A position far outside the latitude of acceptance does not move anyone; it produces contrast and hardening. But repeated exposure widens the latitude of non-commitment, and positions that were previously in the rejection region move into it. Then the next step becomes available.
That is why the technique is executed as a sequence rather than a jump, and why it takes years.
The observable signature is a specific one: a claim that was described as fringe or unthinkable in the recent past being cited without qualification in mainstream commentary. Not agreed with — cited, as a position within the range of the debate. That transition from outside the frame to inside it is the window moving, and it usually happens without anyone having argued for the change in status.
Which suggests the only real countermeasure available to an individual, and it is a documentary one. Keep a record of what you thought about a question before the sustained exposure began, and of what the range of the debate was. Positions drift, and drift is invisible from inside because the reference point moves with you. A note written five years ago is the only reliable evidence that you have moved at all.
Cross-ref: illusory truth and repetition