Legal similarity is a similar reason which governs various cases when compared with each other; for what avails in one similar case will avail in the other. Of things dissimilar, the reason is dissimilar.

Explanation

(English-origin maxim.) Legal similarity means that the same reason governs both cases; where cases share the same rationale, the same rule applies, but where the underlying reason differs, the cases must be treated differently.

Where this applies

• Two cases both involve a government agency exceeding its statutory authority — because the same reason (ultra vires action) governs both, the same rule applies to both.
• A court finds that a case involving unlawful search of a car is governed by the same Fourth Amendment reasoning as a case involving unlawful search of a home — similar reason, similar rule.
• A judge distinguishes two breach-of-contract cases: one involves fraud in the inducement and the other involves honest misunderstanding — different reasons, so different rules apply despite the surface similarity.