Given that no two acts, events, situations, and legal cases are identical, precedential constraint necessarily involves determining which two different cases and situations are relevantly similar. One traditional view posits that these determinations are made on the basis of the rationale in the earlier case, another traditional view sees similarity in the facts of the earlier case plus the outcome, and the Legal Realist view insists that determinations of similarity are ex post attributions based on a judge’s outcome or policy preferences. In contrast to all of these positions, however, is a view informed by research in cognitive psychology. This research supports the conclusion that outcome-independent perceptions of similarity, perceptions based on the experiences and background of the perceiver, not only play a role in the determination of similarity, but often lead precedential reasoners to reason from particular to particular without the conscious mediation of any rule or principle.

Frederick Schauer & Barbara A. Spellman, Precedent and Similarity, in Philosophical Foundations of Precedent, Oxford University Press, 240–251 (2023).