Definition
Fungible things are goods or commodities that are interchangeable with other items of the same kind — meaning one unit is, for legal and commercial purposes, equivalent to any other unit of the same type and quality. A bushel of No. 2 wheat, a barrel of West Texas Intermediate crude oil, a twenty-dollar bill: each is replaceable by another of its kind without loss or difference in value. The legal consequence is that obligations involving fungible things can be satisfied by delivery of equivalent quantity and quality, not the specific item originally tendered.
The concept is drawn directly from Roman civil law, where the category was res fungibiles — things capable of being furnished or restored in kind. The defining characteristic is that the thing is identified by class, weight, measure, or number rather than by individual identity. Non-fungible things, by contrast, have individual characteristics that make them distinct: a particular horse, a specific painting, a named slave in Roman law. These must be dealt with in specie — that is, as the exact thing, not a substitute.
Common Language
Modern common usage (Wiktionary): "Fungible" in ordinary use means replaceable or interchangeable, often extended figuratively to people or roles (e.g., "employees treated as fungible").
Historical common usage (Webster's 1913): Webster's 1913 does not carry a standalone entry for "fungible" as a common English word, reflecting its status as legal and technical terminology with limited general circulation at that time.
The figurative modern use — describing people or positions as interchangeable — borrows the legal concept loosely. In law, fungibility is a precise classification with doctrinal consequences for title, risk of loss, and how obligations are discharged. Calling workers "fungible" in ordinary speech carries no such legal weight, and researchers should not read modern colloquial usage back into historical legal texts where the term has a technical, narrower meaning.
Common Confusion
Fungible things are sometimes confused with consumable things (res consumptibiles). While there is overlap — grain is both fungible and consumable — the categories are distinct. Consumability refers to whether a thing is destroyed by use; fungibility refers to whether a thing is replaceable in kind. Money is fungible and is consumed by use; a library book is neither. The civil law tradition kept these categories analytically separate, and historical sources that blur them should be read carefully.
Core Elements
A thing qualifies as fungible when it satisfies all of the following:
1. Interchangeability by kind: One unit can substitute for another without objection from the party receiving it, because units within the class are equivalent.
2. Identification by measure rather than identity: The thing is described and valued by weight, number, volume, or some other quantitative standard — not by unique characteristics.
3. Class obligation, not specific obligation: The legal duty runs to delivery of the class at the specified quantity and quality, not to the return or delivery of the precise item.
Recognized Forms
/SUBTYPES
Civil law tradition recognized two relevant paired categories:
- Res fungibiles (fungible things): things replaceable in kind, dealt with generically.
- Res non-fungibiles (non-fungible things): things that must be dealt with specifically, such as unique animals, artworks, or identified parcels of land.
Modern commercial law (especially in the UCC framework in American jurisdictions) operationalizes fungibility primarily in the context of goods, securities, and commodities, where it governs warehouse receipts, bulk transfers, and securities entitlements.
Why It Matters in Research
The term is architecturally important in property law, contract law, and commercial law — but researchers must track which legal tradition they are working in.
In civil law materials (Roman, French, Scottish, Louisiana), res fungibiles carries precise doctrinal freight: it governs whether a mutuum (loan for consumption) or a commodatum (gratuitous loan for use) is at issue, which in turn determines who bears the risk of loss and what must be returned. Burrill's entry signals this civil law origin and points to Mackeldey and the Digests — researchers working in civilian jurisdictions or on conflicts questions need to follow that lineage.
In common law materials, the term arrived later and less systematically. Black's (1st and 2nd editions) give the practical commercial definition — weight, measure, number — without the full civilian theoretical structure. Researchers in early American common law sources should not assume the term carries all its civilian implications.
In modern American research, fungibility is operationalized through the Uniform Commercial Code, particularly in Articles 7 (documents of title, warehouse receipts for fungible goods), 8 (investment securities), and 9 (secured transactions in fungible collateral). The statutory language controls, and historical dictionary definitions are a starting point for understanding the concept, not a substitute for UCC text.
A trap for researchers: historical sources sometimes use "fungible" only for movables, treating land as categorically non-fungible. Modern law does not always follow this; commoditized real estate interests (shares in real estate investment trusts, undivided interests in mineral rights) can be treated as functionally fungible in commercial contexts.
Historical Dictionary Support
All three source dictionaries converge on the core definition: things estimated and replaced by weight, measure, or number, belonging to a class rather than identified individually. The alignment is strong.
Burrill's is the most historically grounded, tracing the term to the Latin functionem recipere from the Digests (Dig. 12.1.2) and citing Mackeldey's Civil Law. This is the most useful entry for researchers working in civilian or mixed-jurisdiction sources. Burrill also notes, importantly, that the term was considered "barbarous" — a formed compound without classical Latin authority — which explains why it does not appear uniformly in early texts.
Black's (both editions) give the practical common law formulation, adding the useful contrast: "Horses, slaves, and so forth, are non-fungible things, because they differ individually in value." This illustrative contrast helps researchers calibrate how historical courts applied the concept.
What the historical dictionaries collectively miss: the modern securities and commercial law dimensions. None of the source dictionaries anticipates the UCC, the treatment of fungible investment securities under Article 8, or the role fungibility plays in secured transactions. Researchers should treat these entries as a conceptual foundation, not a complete account.
Jurisdictional Note
Louisiana, as a mixed civil law jurisdiction, applies the civilian concept of res fungibiles with greater doctrinal precision than common law states, particularly in loan and deposit contexts. UCC Article 7 governs fungible goods in warehouse and carrier contexts in all adopting states, with some state-level variations in enactment. Researchers working across common law and civil law jurisdictions should not assume definitional equivalence.