Definition
Commodati actio is a Latin term from Roman civil law meaning the action of loan — specifically, the legal remedy available to a lender to recover a thing that was lent gratuitously (a commodatum) and not returned by the borrower. The action ran in favor of the lender (commodans) against the borrower (commodatarius) who failed to restore the loaned object at the agreed time or upon demand.
The underlying transaction, the commodatum, was a loan for use of a specific thing — not money and not consumable goods — made without compensation. Because the lender received nothing for the loan, the commodati actio served as the enforcement mechanism ensuring the borrower's obligation to return the identical object in undamaged condition.
Why It Matters in Research
Researchers encounter commodati actio almost exclusively in one of two contexts: treatises on Roman civil law or American and English legal scholarship that traces the doctrinal roots of bailment law. The term itself does not appear in modern common-law pleading or statutory codes, but its conceptual lineage runs directly into the law of gratuitous bailments and, in some civilian jurisdictions, into codified loan-for-use provisions.
When reading 18th- and 19th-century American or English equity cases involving goods lent without charge, courts and treatise writers frequently invoked the Roman categories — commodatum, mutuum, depositum — to reason by analogy. A researcher who encounters commodati actio in that literature should understand it as the Roman procedural vehicle, not a surviving cause of action in the forum being discussed.
The Justinianic sources cited in the historical dictionaries — Institutes 3.15.2, Institutes 4.1.16, Digest 13.6, and Codex 4.23 — are the authoritative primary texts. Any deeper research into the scope and limits of the action (e.g., liability for dolus versus culpa, the counter-action commodati contraria for expenses) must go to those sources or to modern Romanist scholarship rather than to the English-language legal dictionaries, which give only the bare definition.
Note the Burrill entry's inclusion of the maxim: Secundum naturam est commoda cujusque rei eum sequi quem sequentur incommoda — "It is according to nature that the advantages of a thing should follow him who is to bear its disadvantages." This principle, embedded in the doctrine of commodatum, reappears in Anglo-American bailment reasoning and in risk-of-loss analysis. Researchers tracing that maxim's usage in American courts will find it cited outside the strict context of commodati actio, so awareness of the broader doctrinal principle is useful.
Historical Dictionary Support
The four source dictionaries are largely in agreement, reproducing substantially the same definition with only minor variation in completeness. Black's (both editions) and Burrill's converge on the identical core formulation: an action given for the recovery of a thing loaned and not returned to the lender, with citation to the Institutes and Digest. Rapalje & Lawrence offer no independent definition, directing the reader to the entry for ACTIO — a reasonable editorial choice given that commodati actio is a species of the broader Roman actio framework.
Burrill's entry is the most complete of the four, adding the Digest 13.6 and Codex 4.23 citations and including the maxim on the natural correspondence between advantage and disadvantage. Black's (1st and 2nd editions) are nearly identical and stop short of the maxim, making Burrill's the preferred source among these dictionaries for a researcher seeking the fuller Roman law context.
None of the historical dictionaries address the distinction between the actio directa (available to the lender) and the actio contraria (available to the borrower for extraordinary expenses or damages suffered). That distinction exists in the Digest and in civilian treatises but is absent from the English-language dictionary tradition, which treats the term as a one-directional lender's remedy. Researchers should not assume the dictionary treatment exhausts the Roman doctrine.
Encyclopedia Cross-Reference
See Law Mind Encyclopedia: Bailment; Roman Law Foundations of Anglo-American Property Law; Commodatum