Definition
Similitudo (Latin: likeness, similarity) is a term from classical Roman and medieval English legal usage denoting the principle of legal similitude — the reasoning by analogy that like cases should be governed by like rules. In the context of English common law, similitudo legalis refers specifically to the doctrine that when two different cases share the same underlying reason or ratio, the legal rule applicable to one should apply equally to the other. It is less a standalone doctrine than a methodological principle: the formal expression of analogical reasoning as a tool of legal extension and interpretation.
The operative formulation, drawn from Coke on Littleton, states: similitudo legalis est, casuum diversorum inter se collatorum similis ratio; quod in uno similium valet, valebit in altero — legal similarity consists in the like reason of different cases compared together; that which has force in one of the like cases shall have force in the other. This is, in essence, a Latin articulation of the maxim underlying precedent-based reasoning and case-by-case legal development.
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Common Confusion
Similitudo is sometimes conflated with the broader concept of analogy as a general logical or rhetorical device. The distinction matters: in legal usage, similitudo carries a normative force — it is not merely an observation that two cases resemble each other, but a claim that the resemblance is legally operative and obligates a parallel outcome. It also differs from strict precedent (stare decisis), which binds by authority. Similitudo operates by reason: the cases need not be identical, only governed by the same ratio.
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Why It Matters in Research
Researchers working in medieval and early modern common law sources will encounter similitudo primarily in glosses, abridgments, and treatises that discuss how courts extended rules to novel fact patterns before a developed doctrine of binding precedent existed. Coke's Institutes are the primary locus; Fleta and other early treatises use the term in similar contexts.
The key research trap is treating similitudo as equivalent to modern analogical precedent. It is an ancestor of that concept, not the same thing. In sources predating the consolidation of stare decisis, similitudo carried more overt methodological weight — courts and commentators had to invoke the principle explicitly because the binding force of cases was not yet assumed. In later common law writing, the principle became absorbed into the general fabric of precedent reasoning and the term itself largely disappeared from English legal discourse.
Researchers tracing the intellectual history of legal reasoning — from Roman law through the glossators, into English common law via Bracton, Fleta, and Coke — will find similitudo a useful node. It connects the civil law tradition of analogical reasoning (reasoning by analogy to the ius commune) with the common law's case-based method, and its appearance in a source is often a signal that the author is engaging with foundational jurisprudential questions about how law extends itself.
Note also the practical limitation: Rapalje & Lawrence contains no substantive entry for similitudo. The only source with a genuine treatment is Burrill. Any research relying solely on Rapalje & Lawrence will miss this term entirely.
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Historical Dictionary Support
Burrill's Law Dictionary is the sole historical shelf source with a substantive entry. The definition is characteristically terse but accurate: it correctly identifies the term as Latin, places it in old English law, provides the core formulation from Coke on Littleton (Co. Litt. 191), and supplies the operative translation. The trailing reference to "white bread" and Fleta, lib. 2, c. 9 appears to be a fragmentary artifact of the source text — possibly a misplaced or corrupted entry remnant — and should not be treated as analytically significant.
Rapalje & Lawrence offers no entry for similitudo; the entry appearing in the source data under that reference number concerns a marine insurance policy term and is clearly misattributed by record, not a substantive treatment of similitudo.
What the historical dictionaries do not provide is any discussion of similitudo's relationship to the broader civil law tradition of analogy, its Roman law antecedents, or its intellectual connection to the later development of ratio decidendi as the basis for binding precedent. Researchers needing that context must go beyond the shelf dictionaries to primary sources in Coke, Bracton, and Fleta directly.
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Jurisdictional Note
Similitudo as a technical term is specific to English common law sources, particularly those written before the eighteenth century. It has no operative use in modern American or English law as a formal doctrine, though the underlying principle animates analogical reasoning throughout all common law jurisdictions.
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Encyclopedia Cross-Reference
Law Mind Encyclopedia — Analogy in Legal Reasoning
Law Mind Encyclopedia — Common Law Method
Law Mind Encyclopedia — Ratio Decidendi
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