Definition
Impossibilis is the Latin adjective meaning "impossible," appearing in classical Roman law texts and carried forward into English legal usage chiefly through the maxims in which it appears. The term itself is rarely used as a standalone legal concept; its significance lies in the foundational maxims it anchors, particularly:
Impossibilium nulla obligatio est — There is no obligation to do impossible things. (Dig. 50.17.185)
Lex non cogit ad impossibilia — The law does not compel the performance of impossibilities.
Together, these maxims express a core principle of legal obligation: a duty cannot arise, be enforced, or survive when performance is objectively impossible. The term surfaces in civil law contexts, equity jurisprudence, and contract doctrine wherever a party seeks relief from an obligation on grounds that it cannot be performed.
Common Confusion
Impossibilis as a civil law Latin term should not be confused with the modern common law doctrine of impossibility of performance, which is a developed contract defense with formal elements and recognized exceptions. The maxims derived from impossibilis state the underlying principle in absolute terms; the modern doctrine applies it with considerable qualification. A researcher encountering impossibilis in a historical source is reading the principle at its most bare — the case law and treatise literature surrounding impossibility of performance represent centuries of judicial refinement on top of that foundation.
Why It Matters in Research
Researchers will encounter impossibilis almost exclusively in two contexts: (1) transcriptions or discussions of Digest maxims in civil law and early equity sources, and (2) nineteenth-century common law treatises that cite the Roman maxims as authority for equitable relief doctrines.
The Burrill entry, though fragmentary, points toward Story's Equity Jurisprudence §§ 1308–1310 as the key bridge between the Roman-law maxim and American equity practice. Those sections address conditions and obligations that become impossible of performance, and Story explicitly draws on the civil law foundation. Researchers working on impossibility, frustration of purpose, or condition-precedent problems in equity should treat impossibilis not as a term of art to be defined in isolation but as a marker pointing toward that broader doctrinal cluster.
A significant research trap: the maxim Lex non cogit ad impossibilia (attributed in Burrill to Hobart 96 and Broom's Legal Maxims) was applied with some frequency in early English common law to excuse non-performance of statutory duties as well as contractual ones. The scope of "impossibility" recognized by courts in that era was narrower than modern doctrine — courts were skeptical of financial hardship or practical difficulty as impossibility, and the maxim was reserved for genuine physical or legal impossibility. Reading historical sources that invoke impossibilis through a modern lens of commercial impracticability will produce anachronistic interpretations.
The Digest reference (50.17.185) situates the principle in the Roman law title De diversis regulis juris antiqui — a collection of general legal rules, not case holdings. This means the maxim was understood as a jurisprudential axiom, not a specific rule of decision, and historical courts citing it were invoking its normative weight rather than a binding precedent.
Historical Dictionary Support
Burrill's entry is minimal but directionally useful. It correctly identifies the Digest locus (50.17.185), cites Hobart's Reports for the lex non cogit maxim, and routes the reader to Story's Equity Jurisprudence — the three nodes that matter most for English and American research. The marginal gloss example ("as if a man promises to give another the moon") signals that the Roman jurists understood impossibilis in its primary sense as physical impossibility, the paradigm case being a promise to perform what nature itself forbids.
What Burrill omits is any treatment of how English equity and common law courts limited and refined the maxim. The entry is purely definitional and maxim-referential, with no engagement with the case law that complicated the principle — particularly the debates over supervening impossibility (where performance was possible at contracting but became impossible later) versus initial impossibility (where performance was impossible from the outset). That doctrinal evolution must be traced through the treatise literature and reporters directly.
Broom's Legal Maxims, cited by Burrill, provides fuller development of Lex non cogit ad impossibilia in context and is the recommended secondary source for researchers needing the English common law application of this principle.
Jurisdictional Note
The maxims rooted in impossibilis were received into both English common law and American equity practice, but their application diverged by the late nineteenth century. American contract law developed the impossibility defense along common law lines that do not map precisely onto either the Roman civil law formulation or English equity. Researchers moving between civil law jurisdictions (where the Digest maxims retain more direct doctrinal force) and common law systems should not assume equivalence.