Definition
De non sane memorie (Law French: "of unsound memory or mind") is a historical legal phrase denoting a person who lacks the mental capacity to manage their affairs or enter into legally binding acts. It is used interchangeably with non compos mentis as a general designation for mental incapacity, without reference to any particular cause or degree of deficiency. The phrase appears primarily in pleadings, conveyancing, and property contexts where the mental competency of a grantor, devisor, or party was placed in issue.
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Common Confusion
De non sane memorie and non compos mentis are functionally synonymous and may be treated as such in historical sources. Researchers should not read significance into an author's choice between them — the selection was typically stylistic or a matter of which linguistic register (Law French vs. Law Latin) was conventional in the document at hand. Neither term maps precisely onto any modern diagnostic category; both simply signal that legal capacity was in question.
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Why It Matters in Research
This term is a navigational challenge because it belongs entirely to historical legal language. It does not appear in modern statutes, restatements, or judicial opinions in active use. Researchers encountering de non sane memorie in primary sources — particularly in Year Books, Plea Rolls, early equity proceedings, or colonial-era conveyancing records — should treat it as a signal to investigate capacity doctrine as it applied at the time of the document, not as a term carrying independent technical weight beyond non compos mentis.
The phrase matters most in three research contexts. First, in property law, a deed or will executed by a person described as de non sane memorie could be challenged or voided, and identifying this phrase in historical pleadings tells the researcher that a capacity challenge is being raised. Second, in equity jurisdiction, courts of chancery developed protective jurisdiction over persons non compos mentis, and de non sane memorie appears in early filings invoking that jurisdiction. Third, in succession and probate materials, the phrase may appear in will contests where the testator's state of mind at execution is disputed.
Because this is Law French, researchers working in English legal records before the 18th century should be alert to spelling variants and Anglicized corruptions. Transcription errors in calendars and abstracts are common. The phrase also sometimes appears in partial or abbreviated form.
The term has no counterpart in American statutory law, where modern frameworks use jurisdiction-specific language ("incapacitated person," "lacks testamentary capacity," "incompetent") grounded in clinical or functional standards. Tracing from de non sane memorie forward requires moving through non compos mentis and into each jurisdiction's capacity doctrine separately.
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Historical Dictionary Support
The three source dictionaries are in full agreement: de non sane memorie means "of unsound memory or mind" and is synonymous with non compos mentis. There is no divergence among them on this point.
Burrill's Law Dictionary is the most useful of the three for research purposes because it supplies reference points — Littleton's Tenures (§ 405) and Plowden's Commentaries (368) — that allow the researcher to locate the phrase in its original doctrinal context. Burrill also cross-references Stock on Non Compotes Mentis, a specialized treatise on mental incapacity that provides fuller treatment of the doctrine the phrase invokes. The two Black's editions add nothing beyond the core equivalence.
What the historical dictionaries do not address: the procedural mechanics by which the condition was established (inquisition of lunacy, office found), the distinctions among types of mental incapacity that non compos mentis itself encompassed, or the equity jurisdiction that developed around persons so designated. Researchers who encounter de non sane memorie in a primary source and want to understand its legal consequences in context will need to move beyond these dictionary entries to those doctrinal sources.
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Encyclopedia Cross-Reference
See Law Mind Encyclopedia: Non Compos Mentis; Mental Capacity in Property and Succession Law.
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