The six elements of a contract are offer, acceptance, consideration, mutual assent, capacity, and legality. Every enforceable agreement in the United States needs all six. Drop any one of them and a court will not enforce the deal, no matter how clear the parties’ intentions seemed at the time. Some of the elements overlap in practice, but each does distinct legal work worth understanding on its own.
Offer
A contract starts when one party proposes a deal with terms clear enough that the other side can simply say “yes” and create a binding agreement. For that proposal to count as a legal offer, three things have to be true: the person making it (the offeror) must intend to be bound if the other side accepts, the terms must be reasonably definite, and the offer must actually reach the person it’s directed to (the offeree).
“Reasonably definite” means the offer identifies who’s involved, what’s being exchanged, at what price, and when performance is expected. Vague statements like “I might sell you my car someday” don’t qualify. Courts ask whether a reasonable person hearing those words would believe a binding deal was on the table.
This is where people confuse an offer with an invitation to negotiate. A store’s newspaper ad, a company’s price list, or goods on a shelf are usually invitations for you to make an offer. The store isn’t promising to sell to everyone who walks in. You can’t “accept” an invitation to negotiate and force a contract into existence.
How an Offer Ends
An offer doesn’t stay open forever. It can end several ways. The offeror can revoke it anytime before acceptance, unless they’ve promised to keep it open (a “firm offer”). The offeree can reject it. The offeree can make a counteroffer, which kills the original. A stated deadline can pass. Either party can die or lose mental capacity. An oral offer made during a conversation typically expires when that conversation ends, unless the offeror says otherwise.
Acceptance
Acceptance is the offeree’s clear, unconditional “yes” to the offer’s terms. It can come through spoken or written words, or through conduct, such as starting the work described in the offer. Silence alone almost never counts. The offeree has to do something affirmative.
Under common law, acceptance has to match the offer exactly. This is the “mirror image rule.” Change any term, even a small one, and you haven’t accepted the original offer. You’ve rejected it and made a counteroffer. The rule has a major exception for sales of goods. Under the Uniform Commercial Code, a clear expression of acceptance can create a binding contract even if the acceptance includes added or different terms from the original offer.
When Does Acceptance Take Effect?
Timing matters. Under the “mailbox rule,” an acceptance sent by mail, email, or fax becomes effective the moment the offeree sends it, not when the offeror receives it. If you mail your acceptance on Monday and the offeror tries to revoke the offer on Tuesday before your letter arrives, the contract was already formed on Monday. The rule applies to standard bilateral contracts but not to option contracts, where acceptance only counts when it reaches the offeror.
Consideration
Consideration is what each side gives up to make the deal work. It’s the “bargained-for exchange.” Each party must promise or provide something of legal value in return for what the other is offering. That value can take many forms: money, goods, services, a promise to do something, or a promise not to do something you’d otherwise have a legal right to do (like agreeing not to sue).
Courts care that consideration exists, but they generally won’t second-guess whether the deal was fair. You can sell a car worth $20,000 for $5,000 and the contract still holds, as long as both sides agreed voluntarily. Extreme lopsidedness might raise a red flag for fraud or coercion, but a court won’t step in just because someone drove a hard bargain.
What doesn’t count as consideration: gifts (one-sided promises with nothing in return), past actions already completed before the promise was made, and “illusory” promises where one side hasn’t actually committed to anything (“I’ll pay you if I feel like it”).
The Promissory Estoppel Exception
Sometimes a promise is enforceable even without traditional consideration. If someone makes a clear promise, you reasonably rely on it, and you suffer real harm because of that reliance, a court may enforce the promise under a doctrine called promissory estoppel. The classic example: an employer promises you a job, you quit your current position and relocate, and the employer backs out. No formal contract existed, but a court could still hold the employer to the promise because walking away would be unjust.
Mutual Assent
Mutual assent, sometimes called a “meeting of the minds,” means both parties genuinely understand and agree to the same terms. Courts don’t try to read anyone’s mind. They apply an objective test: would a reasonable person, looking at the parties’ words and behavior, conclude they’d reached an agreement? Secret reservations or unvoiced misunderstandings don’t invalidate a contract if the outward conduct looked like agreement.
Offer and acceptance are the mechanics through which mutual assent is demonstrated. When one party makes a clear offer and the other cleanly accepts it, mutual assent exists. Problems arise when a contract’s language is ambiguous, capable of more than one reasonable interpretation. In those cases, courts typically look at the surrounding circumstances and the parties’ conduct to figure out what was actually intended, and ambiguous terms are usually interpreted against the party who drafted the contract.
Electronic Signatures
Most contracts today are formed electronically: clicking “I agree,” signing on a tablet, or exchanging emails. The federal Electronic Signatures in Global and National Commerce Act (E-SIGN Act) establishes that a contract or signature cannot be denied legal effect solely because it’s in electronic form.1Office of the Law Revision Counsel. 15 U.S. Code 7001 – General Rule of Validity An electronic signature carries the same legal weight as ink on paper.
Capacity
Both parties must have the legal ability, or capacity, to enter a contract. Most adults have this by default. The groups that don’t include minors (under 18 in most states), people with severe mental impairment, and people so intoxicated they can’t understand what they’re agreeing to.
The key concept here is the difference between a void contract and a voidable one. A void contract never had any legal force. It’s treated as if it never existed. A voidable contract is valid unless the protected party chooses to cancel it. Contracts involving minors or people with mental impairments are typically voidable, not void. The minor can decide to honor the deal or walk away from it. If a minor turns 18 and keeps performing under the contract without objecting, that effectively ratifies the agreement and removes the right to cancel.
One narrow exception: contracts for necessities like food, shelter, or medical care are generally enforceable against minors and incapacitated persons, because allowing people to void those agreements would make it nearly impossible for them to obtain basic needs.
Capacity also comes into play when a contract is signed on behalf of a business. A corporation or LLC can’t sign anything itself; an individual has to sign for it, and whether that person had authority to bind the company is a separate question. The safest approach is to check the company’s bylaws or operating agreement and, if there’s any doubt, get a formal resolution authorizing the specific person to sign.
Legality
A contract’s purpose must be legal. An agreement to commit a crime, evade a statute, or accomplish something a court considers harmful to the public is void from the start. No court will enforce it, and neither party can sue over it. This goes beyond obvious criminal activity. Courts routinely strike down contract terms that violate public policy even when no criminal law is directly broken.
Clauses that try to eliminate one party’s liability for their own negligence are among the most commonly challenged. These exculpatory clauses aren’t automatically invalid, but courts view them skeptically. A waiver that releases a business from liability for its own gross negligence or intentional misconduct will almost certainly fail. Agreements that require unlicensed individuals to perform services requiring a license are another frequent target. If the person performing the work wasn’t legally authorized to do it, the contract governing that work may be unenforceable.
Restrictive covenants in employment contracts, such as non-compete agreements, sit in a gray area. Courts evaluate these case by case, looking at whether the restriction is reasonable in duration, geographic scope, and the business interest it protects. Overly broad non-competes are often struck down or narrowed rather than enforced as written. Several states ban or severely limit non-competes by statute, and this area of law continues to evolve.
When a Contract Must Be in Writing
Having the six elements isn’t always enough. Certain contracts have to be in writing to be enforceable, under a rule called the Statute of Frauds.2Legal Information Institute. Statute of Frauds If a contract falls into one of these categories and isn’t in writing, a court won’t enforce it regardless of whether the other elements are satisfied. Oral contracts outside these categories are generally just as enforceable as written ones.
The most common categories include:
- Contracts for the sale or transfer of land or an interest in land.
- Contracts that can’t be performed within one year of formation.
- Sales of goods worth $500 or more under the Uniform Commercial Code.3Legal Information Institute. Uniform Commercial Code 2-201 – Formal Requirements; Statute of Frauds
- Promises to pay someone else’s debt (“If she doesn’t pay, I will”).
- Contracts made in consideration of marriage, such as prenuptial agreements.
The writing doesn’t have to be a formal contract. A signed letter, email, or text message can satisfy the requirement as long as it identifies the essential terms and is signed (or electronically signed) by the party against whom enforcement is sought.
What Can Still Void a Valid-Looking Contract
A contract can check all six boxes and still be unenforceable if the circumstances surrounding its formation were fundamentally unfair. These defenses usually make the contract voidable, meaning the wronged party can choose to cancel it or let it stand.
- Duress. If someone was forced into a contract through threats or coercion, the agreement is voidable. Physical threats go further and make the contract void entirely, because the “consent” was never real.
- Fraud and misrepresentation. When one party deliberately lies about a material fact to induce the other into signing, the deceived party can rescind the contract and potentially recover damages. Even an honest mistake about a key fact (innocent misrepresentation) can make a contract voidable if the other side relied on it.
- Undue influence. This occurs when someone in a position of trust (a caregiver, financial advisor, family member) uses that relationship to pressure the weaker party into an agreement they wouldn’t have made otherwise.
- Unconscionability. A contract so one-sided that it shocks the conscience can be struck down. Courts look at two dimensions: whether the bargaining process itself was unfair, and whether the resulting terms are oppressively lopsided. A contract is most likely to be found unconscionable when both problems are present.
If any of these defenses apply, the protected party can walk away from the deal even though an offer, acceptance, consideration, mutual assent, capacity, and legality all appear on the face of the agreement.