Signalling

When you know something the other side does not, talk is cheap. To be believed, you must do something a liar would not, and that costly act is a signal.

Signalling is the act of credibly conveying private information to others through a costly action that would not be worth taking if the information were false. In situations of asymmetric information, where one party knows something the other does not, signalling lets the informed party prove what mere words cannot.

The problem of cheap talk

The difficulty signalling solves is that anyone can claim anything. A job applicant can say they are able, a seller can say their product is good, a borrower can say they will repay, but words alone carry no proof, because the dishonest can say exactly the same. For information to be credible, it must be conveyed in a way that the dishonest would find too costly to imitate. The signal works precisely because faking it does not pay.

Costly to fake

The classic example is education as a signal in the job market, an idea developed by Michael Spence. A demanding qualification may signal ability to employers not only because of what is learned but because able people can obtain it more easily than the less able, who would find it too costly to fake. The signal is credible because the cost of acquiring it differs between the types it distinguishes. Warranties signal product quality, since only a confident seller can afford to offer them; a firm spending heavily on advertising may signal that it expects to be around to recoup it.

Signalling and its waste

Signalling is powerful but can be socially wasteful. If education served only to signal pre-existing ability rather than to build it, the resources spent on it would be partly a cost of proving something rather than creating value. Much signalling has this character: an arms race of costly proofs that conveys information but consumes real resources. Recognising when an activity is mainly a signal helps explain behaviour that otherwise looks irrationally extravagant.

Signalling explains how credible information can flow despite the temptation to lie, by tying claims to actions that only the truthful would take. It illuminates everything from education and advertising to courtship and corporate finance, and it carries a sober lesson: that proving what you know can be as costly, and as necessary, as knowing it.