Discounting principle
Also known as: Augmentation–discounting principle
A cause looks less likely when other plausible causes are present.
What it means
An attributional rule, from Kelley, stating that the perceived role of any one cause in producing an effect is reduced when other plausible causes are also present. Its partner, the augmentation principle, says a cause is judged more influential when it produced an effect despite an inhibitory or competing force. Together they describe how observers parse behavior that has multiple possible explanations: a friendly act toward a powerful person is discounted as possibly strategic, while kindness shown at personal cost is augmented as genuine. The principle underlies the overjustification effect, where an external reward leads people to discount intrinsic interest as the cause of their behavior. It is a key tool for understanding how people read sincerity, motive, and credit.
Two rules, one logic
Discounting and augmentation are inverse operations on the same mental arithmetic. An observer treats the possible causes of an act as competing for explanatory credit. When several sufficient causes are present, each is assigned less weight, because any one of them could have produced the effect on its own — that is discounting. Augmentation is the mirror case: when an act occurs despite a force that should have suppressed it, the facilitating cause must have been strong enough to overcome the obstacle, so it earns more credit. Both follow from treating behavior as the visible output of a hidden causal contest, and from an implicit assumption that a fixed quantity of cause is available to be divided among the candidates.
When the logic is sound
Morris and Larrick (1995) showed that discounting is a valid inference only for certain causal structures. If two causes are each independently sufficient, then observing one lowers the probability that the other was needed, and discounting follows from probability theory. But if the causes are necessary conditions that must combine to produce the effect, learning that one is present says nothing against the other, and discounting is simply a mistake. People often discount reflexively without checking which structure they face. The principle is therefore not a bias in itself; it is a sound heuristic that misfires when applied to causes that add up rather than substitute for one another.
What the evidence shows
Kruglanski and colleagues (1978) separated discounting from Kelley's covariation principle and from augmentation, finding that they operate on different parts of the attribution process rather than being one mechanism. The most consequential application is the overjustification effect: paying people to do something they already enjoy leads them to discount their own interest as the cause. A large meta-analysis (Deci, Koestner, and Ryan, 1999) confirmed that tangible, expected rewards reliably reduce later intrinsic motivation, though the effect is moderated by how the reward is framed. Developmental research complicates the tidy story, since the rule emerges slowly and younger children frequently fail to discount at all.
Where it breaks down
The principle assumes observers correctly identify the competing causes, and they routinely do not. People systematically under-weight situational forces — the correspondence bias — so a plausible external cause that should trigger discounting is often ignored, and the behavior is read as disposition anyway. Motivated reasoning skews it further: we discount the sincerity of opponents while crediting the same act from allies. And because the fixed-pie assumption fails for causes that combine, reflexive discounting can strip away credit that was genuinely earned. This is an underappreciated cost when evaluating praise, confessions, and testimony, where a real cause and a suspicious one can both be operating at once.
Examples
A glowing testimonial from a paid spokesperson is discounted, while the same praise from an uncompensated stranger carries more weight.
A child who drew for fun is paid per picture for a month. When the money stops, so does the drawing — reward became the visible cause, so interest gets discounted.
A confession that arrives with a plea bargain carries less weight than an unprompted one. The deal is an obvious cause of the words, so they stop being read as guilt.
A sprinter who sets a record running into a stiff headwind is judged faster than one who set the same time with a tailwind. The opposing wind is a competing cause, so ability gets augmented.
First described in Harold Kelley (1971; 1973).
Key references
- Deci, E. L., Koestner, R., & Ryan, R. M. (1999). A meta-analytic review of experiments examining the effects of extrinsic rewards on intrinsic motivation. Psychological Bulletin, 125(6), 627-668. doi.org/10.1037/0033-2909.125.6.627
- Morris, M. W., & Larrick, R. P. (1995). When one cause casts doubt on another: A normative analysis of discounting in causal attribution. Psychological Review, 102(2), 331-355. doi.org/10.1037/0033-295X.102.2.331
- Kruglanski, A. W., Schwartz, J. M., Maides, S., & Hamel, I. Z. (1978). Covariation, discounting, and augmentation: Towards a clarification of attributional principles. Journal of Personality, 46(1), 176-189. doi.org/10.1111/j.1467-6494.1978.tb00609.x
- Kelley, H. H. (1973). The processes of causal attribution. American Psychologist, 28(2), 107-128. doi.org/10.1037/h0034225