The Building Blocks of Every Contract

Contract law is one of the most heavily tested subjects on paralegal certification exams, and formation is where nearly every contracts question begins. Before a court will enforce a promise, the parties must have created a valid contract. That requires mutual assent (an offer and an acceptance), consideration, and the absence of defenses such as lack of capacity, illegality, or fraud.

This guide breaks formation into the questions exam writers love to ask, with practical examples you can apply on test day and on the job.

What Is an Offer?

An offer is a manifestation of willingness to enter a bargain, made in a way that would justify the other party in understanding that their assent will conclude the deal. An offer has three essential features:

Intent to be bound: The offeror must objectively show a present intent to contract, not merely to negotiate.
Definite terms: The offer must be reasonably certain about the parties, subject matter, price, and quantity. Under the UCC, missing terms can often be filled in, but quantity usually cannot.
Communication: The offer must be communicated to the offeree.

Not everything that looks like an offer is one. Advertisements, price quotes, and catalogs are generally invitations to negotiate rather than offers. A narrow exception arises when an ad is specific enough and leaves nothing open for negotiation, such as "first come, first served" language. Preliminary statements like "I might sell for around $5,000" also fall short.

How Does an Offer End?

An offeree's power of acceptance does not last forever. Know the ways an offer terminates:

Lapse of time: The offer expires at the stated deadline or after a reasonable time if none was given.
Revocation: The offeror withdraws the offer before acceptance. Revocation is effective when received by the offeree.
Rejection: The offeree refuses the offer. Rejection is effective on receipt.
Counteroffer: A counteroffer operates as a rejection of the original offer and creates a new one.
Death or incapacity: The death or loss of capacity of either party generally ends the offer.
Destruction of the subject matter or supervening illegality.

An option contract is an exception. When the offeree gives consideration to keep an offer open, the offeror cannot revoke during the option period. Under the UCC, a firm offer by a merchant, in a signed writing promising to hold the offer open, is irrevocable for the stated period (up to three months) without consideration.

What Counts as Acceptance?

Acceptance is the offeree's unequivocal agreement to the terms of the offer. At common law the mirror image rule applies: the acceptance must match the offer exactly. Any change in terms is a counteroffer. UCC Section 2-207 relaxes this rule for the sale of goods, allowing a contract to form even when the acceptance contains additional or different terms, unless acceptance is expressly made conditional on assent to those terms.

Only the person to whom the offer was made may accept it. Silence is generally not acceptance, though exceptions exist when parties have a prior course of dealing or when the offeree takes the benefit of offered services knowing they were not free.

What Is the Mailbox Rule?

Under the mailbox rule, an acceptance sent by a reasonable method of communication is effective when dispatched, not when received. This is a favorite exam topic. Remember the exceptions: an option contract requires receipt of acceptance, and if the offeree sends a rejection first and then an acceptance, the first one received controls. Offers may also specify that acceptance is effective only on receipt, which overrides the rule.

Unilateral Versus Bilateral Contracts

A bilateral contract is formed by an exchange of promises. A unilateral contract is formed when the offeree performs the requested act, such as a reward offered for returning a lost dog. In a unilateral contract, once the offeree begins performance, the offeror generally cannot revoke for a reasonable period to allow completion.

What Is Consideration?

Consideration is the bargained-for exchange of legal value. Each side must give up something they were not already obligated to give up, or promise a benefit to the other. It may be a promise to act, a promise to refrain from acting, or a present performance. Courts do not weigh adequacy, so a promise to sell a car for one dollar can be supported by consideration if the exchange was truly bargained for. They do look at whether the exchange was real, which is why a sham or nominal recital may fail.

Key doctrines to memorize:

Past consideration is not consideration. A promise made in return for something already done lacks the bargained-for element.
Pre-existing duty rule: A promise to do what you are already legally bound to do is not consideration. Some states and the UCC allow good-faith modifications without new consideration.
Illusory promises: A promise that leaves performance entirely to the promisor's discretion, such as "I will buy what I want," does not count.
Settlement of a good-faith dispute can supply consideration.

What If There Is No Consideration?

Some promises are enforceable even without it. Promissory estoppel allows recovery when the promisor should reasonably expect reliance, the promisee actually and reasonably relied, and injustice can be avoided only by enforcing the promise. Other exceptions include written firm offers under the UCC, promises to pay debts barred by the statute of limitations, and charitable subscriptions in some states.

How Do Paralegals Use These Rules?

When reviewing a dispute, a paralegal builds a timeline of communications to identify what the offer was, when it was accepted, and whether it was revoked or countered in the meantime. Emails, text messages, and signed term sheets all become critical evidence. Accurate chronology often decides whether a contract exists at all.

Study Strategy

Build a quick checklist: offer, acceptance, consideration, then defenses. Practice applying it to short fact patterns. Our contract law flashcards drill terms such as mirror image rule, firm offer, and promissory estoppel. When you are ready for scenario-based questions with explanations, sign up for free and start practicing, or review the features included in each plan on the pricing page.

Contract Formation: Offer, Acceptance, and Consideration Explained