Types of contracts: express and implied, unilateral and bilateral

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Two independent classifications

Express and implied describe how agreement is communicated. Unilateral and bilateral describe what is exchanged. One contract can receive a label from each pair.

Express or implied in fact

An express contract states the agreement in spoken or written words. An owner asking for cleaning at an agreed price and a cleaner verbally promising to do it form an express agreement. Express does not mean written.

An implied in fact contract is inferred from conduct and circumstances showing mutual assent. A manager and cleaner with an established paid arrangement may indicate another agreement through requesting, performing, and accepting the service without restating the terms. A private expectation alone is insufficient. An implied in law obligation, or quasi contract, is a remedy against unjust enrichment, not an actual agreement inferred from conduct.

Bilateral or unilateral

A bilateral contract exchanges a promise for a promise. A typical purchase agreement exchanges the seller's promise to convey for the buyer's promise to pay, subject to its terms. Obligations arise before the promised closing performance.

A unilateral offer requests performance in exchange for a promise. An owner offering a reward for returning lost keys requests the act of returning them, not a promise to search. Merely promising to look does not supply that acceptance. The classification concerns the requested exchange, not the number of people or signatures.

Two rows ask separate questions. How is agreement shown? Words indicate express agreement; conduct indicates implied in fact agreement. What exchange is requested? A promise for a promise is bilateral; a promise for requested performance is unilateral. A contract can have one label from each row. — Classify communication and exchange separately.

A written reward offer can be express and unilateral. A spoken exchange of promises can be express and bilateral.

Keep enforceability separate

Real estate transactions may require a writing. Calling an oral agreement express does not establish enforceability. First identify words versus conduct, then promises versus requested performance, and separately address any enforceability issue the question asks.

Key terms

Sample questions

Which feature makes an agreement express?

The parties state their agreement in words.
The parties infer agreement from conduct.
The parties exchange reciprocal promises.
The parties finish their promised performances.

Reveal answer

Correct answer: The parties state their agreement in words.

Express describes agreement communicated in spoken or written words.

An owner verbally offers a painter $900 for a room, and the painter verbally promises to paint it for that amount. How is their agreement classified?

Implied in fact and bilateral
Express and bilateral
Express and unilateral
Implied in fact and unilateral

Reveal answer

Correct answer: Express and bilateral

Spoken words make the agreement express; the exchanged promises make it bilateral.

A manager and cleaner have an established paid arrangement. Without discussing new terms, the manager indicates another vacant unit, and the cleaner knowingly cleans it for the usual fee with the manager’s acceptance. What best explains agreement?

A quasi contract must replace mutual assent.
Their conduct supports an implied in fact contract.
The absence of new words prevents agreement.
The usual price makes the new agreement express.

Reveal answer

Correct answer: Their conduct supports an implied in fact contract.

The parties’ conduct, understood against their established arrangement, indicates mutual assent.

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