Definition
A Latin term meaning "to compute, reckon, or account." In legal contexts, *computo* functions both as a verb (the act of reckoning or calculating) and as the root of procedural phrases that appear in the old common law action of account. The term is less a standalone legal concept than a building block for several formal Latin phrases used in account proceedings, each carrying distinct procedural significance.
The related noun form, *computus* (also written *compotus*), denotes an account itself — specifically the rendering of accounts that was the subject of the writ of account, one of the earliest common law writs for recovering money owed by an agent, bailiff, guardian, or other fiduciary who had received another's funds.
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Common Confusion
*Computo* and *computus* are often treated as interchangeable in older legal texts, and some sources list one as a cross-reference to the other without explanation. They are grammatically related but functionally distinct: *computo* is the verb form (to account, to reckon), while *computus* is the noun form (an account, a reckoning). The writ itself was called a writ *de computo* — using the noun's ablative — not a writ *de computus*. Researchers encountering either form in historical records should read the surrounding procedural context carefully before treating the terms as synonymous.
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Why It Matters in Research
Researchers encounter *computo* almost exclusively in the context of the medieval and early modern action of account (*actio de computo*), a predecessor to modern accounting and fiduciary liability actions. Several practical traps arise:
**Phrase recognition.** *Computo* rarely appears alone in case records or pleading books. It surfaces embedded in Latin phrases that functioned as formal terms of art: *insimul computassent* ("they reckoned together," the basis of an indebitatus count), *plene computavit* ("he has fully accounted," a plea in bar), and *quod computet* ("that he account," the initial judgment ordering a defendant to account before auditors). Each phrase marks a different procedural stage. Misreading one for another distorts the stage of proceedings a source is describing.
**Auditors and the two-stage proceeding.** The action of account had an unusual two-stage structure: first, a judgment *quod computet* ordering the defendant to appear before auditors; second, the auditors' determination of the balance, followed by final judgment. Sources referencing *computo* may describe either stage. A record mentioning *plene computavit* has reached the second stage; one mentioning *quod computet* has not yet left the first.
**Spelling variation.** Historical records render the term in multiple forms — *computo*, *computus*, *compotus*, *computum* — reflecting both Latinate grammatical declension and medieval scribal inconsistency. Corpus searches limited to a single spelling will miss related records.
**Relationship to assumpsit.** By the seventeenth century, the action of account was being displaced by the more flexible action of assumpsit, particularly via the *indebitatus* count whose formula derived from *insimul computassent*. Researchers tracing the history of quasi-contract or unjust enrichment doctrine will find *computo*-family terms at the pivot point between the old real/personal action structure and the modern law of obligations.
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Historical Dictionary Support
Burrill and Black agree on the essential meaning — to count, reckon, or render account — and both treat *computo* primarily as a gateway to related phrases rather than as an independent doctrinal term. Burrill directs the reader to *computus* and grounds the term in the writ of account, quoting the Registrum Brevium's formula (*quod juste et sine dilatione reddat rationabile computum suum*) to show that the writ itself demanded a "reasonable account." Black organizes the entry around the three derivative phrases (*insimul computassent*, *plene computavit*, *quod computet*), treating *computo* as the etymological key to unlocking their meaning rather than as a term with independent legal force.
Neither source addresses the procedural mechanics of the auditor stage in depth, and neither connects *computo* to its eventual absorption into assumpsit doctrine — a gap that matters for researchers working in the seventeenth and eighteenth century corpus, when the action of account was in visible decline.
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Encyclopedia Cross-Reference
See Law Mind Encyclopedia: Action of Account; Insimul Computassent; Quasi-Contract.
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