Definition
To perform, in law, is to carry out or discharge an obligation according to its terms. In contract law specifically, performance means executing what a party promised — whether by doing something (delivering goods, rendering services, paying money) or refraining from doing something (a covenant not to compete, for example). Performance is the primary means by which contractual obligations are discharged, and it is conceptually distinct from payment, which is treated in legal usage as a separate mode of discharge even though payment is itself a form of action in fulfillment of a promise.
Performance may be complete (full satisfaction of all contractual duties), substantial (sufficient fulfillment to entitle a party to the counter-performance, subject to damages for any deficiency), or partial (some progress made but not enough to trigger the other party's duties). The legal significance of each category differs sharply: full performance discharges the obligation entirely; substantial performance typically prevents forfeiture while leaving a damages claim open; partial performance may or may not excuse the other party's counter-performance depending on whether the breached term was a condition.
Common Language
Modern common usage (Wiktionary): To do something; to execute a task; to exhibit expected functioning or behavior; also, to act before an audience or to act in accordance with a contract.
Historical common usage (Webster's 1913): To carry through; to bring to completion; to achieve; to accomplish; to execute; to discharge or fulfill (a duty, promise, or vow); also, to represent or play a role.
The gap between ordinary and legal usage is narrow but consequential. Common language treats "perform" as synonymous with simply doing something. Legal usage sharpens the term: to perform a contract means to do it according to its specific terms, not merely to do something in its neighborhood. That precision matters because partial or defective action may look like performance in ordinary speech while constituting breach in law.
Common Confusion
PERFORM vs. TENDER: To perform is to actually carry out the promised act. To tender is to offer to perform — to present oneself as ready and willing without necessarily completing execution. The distinction has procedural consequences: a valid tender can shift the burden of refusal onto the other party and, in some contexts, stop the running of interest or excuse a technical default.
PERFORM vs. DISCHARGE: Performance is one mode of discharging a contractual obligation, but discharge is the broader category. Obligations can also be discharged by agreement (rescission, accord and satisfaction), by operation of law (impossibility, frustration), or by breach accepted as repudiation. Conflating the two leads to analytical errors when researching cases involving non-performance that did not result in liability.
Why It Matters in Research
The word "perform" appears across an enormous range of legal instruments and doctrines, which creates indexing and retrieval challenges in historical sources. When researching pre-twentieth-century materials, be alert to the fact that courts and treatise writers often used "perform" to describe any act in discharge of a duty — including payment — while modern usage and the Black's entries themselves carve payment out as a distinct category. A passage in an older source describing failure to "perform" a money obligation may be analyzing what modern law calls nonpayment, with potentially different remedial consequences.
The substantial performance doctrine is the single most important doctrinal context for this term. Courts developed the doctrine to prevent the harsh result of total forfeiture when a party had done most of what was promised but fell short in some respect. Researchers tracing this doctrine should not expect to find "substantial performance" as a fixed phrase in early materials; older sources may discuss it under headings like "conditions precedent," "entire vs. divisible contracts," or simply analyze whether a party "performed" for purposes of recovering on the contract. Cross-reference the encyclopedia entries on substantial performance and the order of performance to navigate these terminological variations.
Jurisdictional variation in what counts as sufficient performance — particularly in construction and service contracts — is significant. The UCC's treatment of performance for goods contracts (including the perfect tender rule for single-delivery contracts under Article 2) differs materially from common law substantial performance analysis. Researchers must identify whether a historical or current source is operating under common law or UCC principles before generalizing conclusions about what "performance" requires.
Historical Dictionary Support
Both the first and second editions of Black's Law Dictionary give essentially identical definitions, indicating no meaningful editorial evolution between editions on this term. The shared formulation — to execute, fulfill, or accomplish an obligation according to its terms — tracks the general common law understanding without deviation. Both editions note the action-or-omission duality and both explicitly distinguish performance from payment, flagging the latter as a separate category.
What the historical Black's entries do not address is the graded quality of performance: the distinction between full, substantial, and partial performance is entirely absent. This is not surprising given that Black's is a dictionary rather than a treatise, but it means that researchers relying solely on the Black's definition will find no guidance on the doctrinal structure that makes "perform" legally interesting. Willistion's treatise on contracts and later Corbin's work are the more productive historical sources for that analysis.
The Webster's 1913 definition is notably inclusive — it encompasses theatrical performance and the fulfillment of promises in a general moral sense alongside contract execution. This breadth is useful context for reading older judicial opinions where "perform" may carry some of that moral register in addition to its technical meaning.
Jurisdictional Note
Under UCC Article 2, the standard for performance of a seller's delivery obligation is generally the perfect tender rule — the goods and tender must conform in every respect to the contract — though significant exceptions apply (cure rights, installment contracts). Common law contract doctrine, governing services and most non-goods transactions, applies the more forgiving substantial performance standard. Researchers working across both bodies of law should not assume consistent meaning.
Encyclopedia Cross-Reference
Performance — Tender of Performance (The Law Mind Contracts & Commercial Law Encyclopedia)
Performance — Duties and Order of Performance (The Law Mind Contracts & Commercial Law Encyclopedia)
Performance — Substantial Performance Doctrine (The Law Mind Contracts & Commercial Law Encyclopedia)