Definition
A Latin adverb used in legal writing and judicial opinions to signal the opposite conclusion, an exception, or a contrasting rule applicable to a different set of facts. When a writer states a legal proposition and then introduces a qualification or reversal, secus marks that turn. It functions as a concise shorthand for "but the rule is otherwise" or "the contrary holds" — typically appearing without elaboration, trusting that the reader understands the contrasting proposition follows.
In practice, secus performs two slightly distinct functions: (1) signaling a direct negation of the preceding rule ("X is true; secus if Y"), and (2) introducing an exception or carve-out that applies under a different factual posture. Context determines which function is in play.
Common Confusion
Secus and aliter are functionally interchangeable in legal writing and are sometimes confused or treated as distinct when they are not. Both mean "otherwise" or "to the contrary" and both introduce exceptions or contrasting rules. No substantive difference in meaning separates them. When researching a point of doctrine across multiple historical sources, treat the two terms as equivalents and do not assume a different rule applies simply because one source used secus and another used aliter.
Why It Matters in Research
Researchers working in older case reporters, equity reports, and common law treatises will encounter secus with some regularity, particularly in English authorities from the seventeenth through nineteenth centuries and in early American decisions drawing on those sources. The word appears without definition in those texts and can be easily misread or skipped by a reader unfamiliar with it, causing the researcher to miss an exception or a contrary rule that the author considered important enough to flag.
The key navigational trap is structural: secus is often positioned at the opening of a sentence or clause, and its brevity can cause it to blend into surrounding text. When you see secus, stop and identify what proposition came immediately before it. The sentence or clause following secus states either the exception or the opposite rule — and that opposite rule may be the controlling point for the case or problem at hand.
Secus connects closely to aliter, which performs nearly the same function. Burrill's cross-reference to aliter is useful: when a source uses one term, check whether the same source or a related authority uses the other, since both may appear across the same body of doctrine without consistent preference for one over the other.
Because secus is a term of textual structure rather than substantive doctrine, it does not vary by jurisdiction in the way that a substantive legal standard would. However, its frequency varies: English equity reporters and chancery materials use it more heavily than American state court opinions, which began favoring plain English glosses ("but otherwise," "the contrary rule applies") as the nineteenth century progressed. By the twentieth century, secus had largely disappeared from American judicial writing. Researchers working backward from modern doctrine into historical sources should be prepared to encounter it in the older materials even if the modern sources on the same question contain none.
Historical Dictionary Support
The historical dictionaries are in close agreement. Black's (both editions) define secus as "otherwise; to the contrary" and note its use to signal the converse of a preceding proposition, a rule applicable to different facts, or an exception to a stated rule. The second edition is marginally more complete in articulating these three functions. Anderson's entry is damaged in the surviving text and contributes little beyond the core gloss. Burrill adds the synonym aliter and two early English case references, which confirms that the term was current in English common law and equity practice well into the eighteenth century; he also notes the secondary sense of "amiss; contrary" from Calvin's Lexicon, though this secondary sense is rare in legal usage and researchers are unlikely to encounter it.
None of the historical dictionaries offer extended treatment, which reflects the term's nature: it is a connective or transitional word, not a doctrine, and the dictionaries treat it accordingly. The Wiktionary gloss ("otherwise, to the contrary") matches the historical legal dictionaries exactly, which is consistent with the term's function — it carries the same meaning in legal Latin as in classical Latin prose.