Definition
Impossibility, in law, refers to a condition in which performance of a contractual obligation or legal act cannot be accomplished — either because nature, law, or logic renders it incapable of being done. It operates most prominently as a defense to breach of contract, excusing a promisor from liability when supervening circumstances make performance genuinely impossible after the contract was formed.
The doctrine has three principal applications:
1. IMPOSSIBILITY AS A CONTRACT DEFENSE: When a party is unable to perform due to circumstances beyond their control that arose after contract formation, impossibility may discharge the obligation entirely or partially. The classic rule required true impossibility — the thing literally could not be done — not mere hardship or increased difficulty.
2. IMPOSSIBILITY IN CONDITIONS AND CONSIDERATION: Where a contract condition or the consideration for a promise is itself impossible to fulfill, the law may treat the agreement as void or unenforceable from the outset, rather than discharging a duty that once existed.
3. IMPOSSIBILITY IN EQUITY: Courts of equity apply the doctrine in deciding whether to grant specific performance or other coercive relief. A court will not order the impossible; impossibility of performance is therefore a recognized defense to equitable remedies as well as at law.
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Common Language
Modern common usage (Wiktionary): Something that is impossible; the quality or state of being unable to do something.
Historical common usage (Webster's 1913): The quality of being impracticable; that which cannot be thought, done, or endured. Webster's also recognized the philosophical subset — logical impossibility — as a condition involving inherent contradiction.
The gap between common and legal meaning is significant in one direction: ordinary usage treats "impossible" loosely, encompassing things that are merely very difficult, highly unlikely, or practically inconvenient. Legal doctrine does not. Courts have consistently distinguished true legal impossibility from mere hardship, commercial impracticability, or frustrated expectations. A researcher encountering "impossibility" in a historical legal source should not assume it maps onto casual modern usage of the word.
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Common Confusion
IMPOSSIBILITY vs. IMPRACTICABILITY: Modern contract law — particularly under the Uniform Commercial Code and Restatement (Second) of Contracts — substantially expanded the classical impossibility doctrine into the broader doctrine of commercial impracticability, which does not require that performance be literally impossible, only that it become commercially unreasonable due to unforeseen circumstances. Historical sources use "impossibility" where modern courts and scholars would often say "impracticability." A researcher reading nineteenth-century treatises or cases should not assume the classical "impossibility" standard maps directly onto modern doctrine.
IMPOSSIBILITY vs. FRUSTRATION OF PURPOSE: These are related but distinct doctrines. Frustration applies when performance remains possible but the purpose for which the contract was made has been destroyed by supervening events. Impossibility applies when performance itself cannot occur. Historical sources sometimes blur this line; the doctrines were not always clearly separated before the twentieth century.
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Core Elements
The historical sources (Rapalje & Lawrence, Bouvier, Black's) converge on a tripartite classification that structures the doctrine:
PHYSICAL IMPOSSIBILITY: Performance is contrary to the laws of nature or physically incapable of execution. May be absolute (impossible for anyone) or relative (impossible for this particular promisor). Only objective — absolute — physical impossibility traditionally excuses performance; relative impossibility (personal incapacity) required closer analysis.
LEGAL IMPOSSIBILITY: Performance would require violation of law, or the law itself intervenes to prohibit what was promised. A contract to perform a now-illegal act may be discharged on this basis.
LOGICAL IMPOSSIBILITY: The act or condition is self-contradictory — it cannot be conceived without internal inconsistency. This category has more philosophical than practical legal significance, but it appears consistently in the historical taxonomy.
Timing matters independently: impossibility existing at contract formation (initial impossibility) may render the contract void for want of consideration or mutual assent, while supervening impossibility — arising after formation — operates as a discharge doctrine.
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Why It Matters in Research
SHIFTING DOCTRINE OVER TIME: The classical common law rule was strict — only objective impossibility excused performance. The twentieth century saw a significant doctrinal expansion, first through case law (particularly after the World War I-era cases in England and the United States) and then through the UCC and the Restatements, which introduced impracticability and frustration as parallel doctrines. A researcher working in historical sources must track where on this continuum a given authority sits. An 1880 treatise on impossibility describes a materially narrower doctrine than a 1980 treatise using the same word.
OBJECTIVE VS. SUBJECTIVE IMPOSSIBILITY TRAP: The classical rule excused only objective impossibility — what no one could do — not subjective impossibility — what this promisor cannot do. Historical sources are explicit about this. Researchers analyzing older cases must determine which form of impossibility was at issue before drawing conclusions about the holding.
CORPUS CONNECTIONS: The doctrine of impossibility intersects substantially with supervening events (war, government action, destruction of the subject matter), conditions precedent, discharge and excuse in contract, and the law of specific performance in equity. In the Law Mind corpus, the contracts and remedies encyclopedias both address the doctrine from different angles — the contracts entry addresses discharge; the remedies entry addresses the defense to equitable enforcement. Both should be consulted for complete coverage.
CONSIDERATION AND INITIAL IMPOSSIBILITY: Bouvier flags an important distinction that researchers sometimes overlook — impossibility affecting the consideration for a promise is analytically different from impossibility affecting the promise itself. This distinction can determine whether a contract is void ab initio or merely dischargeable.
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Historical Dictionary Support
The major historical dictionaries agree on the fundamental definition and the tripartite physical/legal/logical taxonomy. Black's (both editions) and Rapalje & Lawrence closely parallel each other in organizing the doctrine around these categories. Bouvier adds a more analytical treatment, expressly noting that the legal consequences of impossibility depend on its classification, the time it arises, and whether it affects the promise or the consideration — a nuance that Black's does not develop as fully.
Anderson's Dictionary of Law offers no independent treatment, directing the reader to "possibility" — unhelpful for most research purposes.
The historical dictionaries are largely silent on what became the most practically important development: the transition from strict impossibility to the broader impracticability standard. This is expected — the sources predate the major doctrinal shift — but it means a researcher relying solely on these authorities will encounter a doctrine that is narrower and more categorical than what modern law applies. The historical sources also do not address frustration of purpose as a separate doctrine; that conceptual separation developed primarily in the twentieth century.
The Black's 2nd edition entry references two cases (Klauber v. San Diego Street-Car Co. and Reid v. Alaska Packing Co.) as illustrative authorities. These are real cases and appropriate for period research, though a researcher should confirm their subsequent treatment in light of evolved doctrine.
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Jurisdictional Note
American jurisdictions vary in how they have absorbed the expanded impracticability standard. UCC Article 2 (goods contracts) codifies commercial impracticability as the operative standard. For common law contracts (services, real property), jurisdictions differ on how closely they track the Restatement (Second) position versus the classical impossibility rule. Some states have been more conservative in expanding beyond true impossibility.
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Encyclopedia Cross-Reference
contracts_71: Discharge — Impossibility of Performance (Objective Impossibility) — The Law Mind Contracts & Commercial Law Encyclopedia
remedies_58: Impossibility and Impracticability as Defenses to Equitable Relief — The Law Mind Remedies & Equity Encyclopedia
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