Deposition
Appeal to Probability
In the matter on the record
An informal logical fallacy in which a possible outcome is treated as probable or certain merely because it is non-zero.
Q. The claim on the record
The appeal to probability (also called appeal to possibility) is not an empirically studied cognitive bias in psychology; it is a classification from informal logic and rhetoric. It was codified in mid-20th-century logic textbooks such as Copi's Introduction to Logic and appears in standard fallacy catalogs. The error consists of inferring that because an event could happen, it probably will happen. There are no controlled experimental studies establishing it as a distinct psychological mechanism with measurable effect sizes. It is closely related to Murphy's Law ('anything that can go wrong will go wrong') and is a staple of critical-thinking education. Because it lacks an experimental literature, it should be treated as a folk-concept or pedagogical label rather than a validated cognitive phenomenon.
A. For the defense
There is no experimental literature to replicate. The appeal to probability is a fallacy label used in logic education, not a finding from cognitive psychology. Related phenomena such as probability neglect have been studied, but the appeal to probability itself has no empirical grounding as a distinct bias.
A. The mechanism in dispute
Because appeal to probability is a logical fallacy rather than a validated cognitive bias, no well-established psychological mechanism exists. Speculatively, it may reflect overuse of the representativeness heuristic (conflating possibility with likelihood) or probability neglect (focusing on the existence of a risk rather than its magnitude). These are not distinct mechanisms but rather applications of broader heuristics documented by Kahneman and Tversky.
Q. On redirect
It may simply be a rhetorical move used to heighten urgency rather than a genuine cognitive error. No experiments distinguish it from the availability heuristic or probability neglect.
Matter of record — tech
Murphy's Law in engineering culture. The adage 'anything that can go wrong will go wrong' is a colloquial expression of appeal to probability. While useful as a precautionary principle, treating every possible failure as inevitable can lead to over-engineering and wasted resources.
Matter of record — finance
Lottery players justifying excessive ticket purchases. Individuals have been documented arguing that because winning the lottery is possible, persistent play will eventually lead to a jackpot. This reasoning ignores the extremely low base rate of winning and illustrates the fallacy in financial decision-making.
The ruling — replication folk-concept
No competent evidence on the record
Require explicit probability estimates and compare them to base rates. Ask 'what is the actual frequency of this outcome?' rather than accepting possibility as sufficient evidence.
Certified by Irving M. Copi, 1961 — Introduction to Logic. Reporter's note: This entry is weakly grounded because appeal to probability is not a validated cognitive bias with experimental literature. It is a folk-concept from logic textbooks. No DOI-linked empirical studies were found. Its inclusion in bias catalogs is pedagogical, not scientific.
Cited authorities
- Probability Neglectmechanistically-linkedBoth involve ignoring quantitative probability information, but probability neglect has been studied experimentally (Sunstein, 2002) whereas appeal to probability has not.
- Base Rate FallacysiblingBoth involve errors in probabilistic reasoning, but the base rate fallacy ignores prior probabilities while appeal to probability inflates possibility to probability.