The basics of contract law come down to a short list: a clear offer, an acceptance that matches it, something of value exchanged on both sides, parties who can legally agree, a genuine meeting of the minds, and a lawful purpose. Get all of those right and you have an agreement a court will enforce. Miss one, and you may be left with nothing but a handshake and a bad feeling. The rest of the rules, from when a deal has to be written down to what you can recover if the other side walks away, build on that foundation.
What Makes a Contract Legally Binding
A contract starts with an offer. The person making it has to signal, clearly enough that a reasonable person would understand, that saying yes seals the deal.1OpenCasebook. Restatement of Contracts Second 3, 17, 18, 22, 23, 24 The terms need enough detail that the other side knows what they’re agreeing to: price, subject matter, key obligations.
Not every proposal counts. “I’d probably sell this car for $10,000” opens a negotiation; it doesn’t lock the speaker in. Advertised prices work the same way. When a store posts a price, it’s inviting you to offer to buy, not committing to sell. People assume a posted price binds the seller. It usually doesn’t.
Acceptance is the next piece. Under the common-law mirror image rule, the acceptance has to match the offer’s terms exactly.2Legal Information Institute. Mirror Image Rule Change the price, change the timeline, change anything, and the response becomes a rejection plus a counteroffer. The back-and-forth continues until both sides land on identical terms or someone walks.
Timing matters too. The mailbox rule treats an acceptance as effective the moment it’s sent by a reasonable method, not when it arrives.3Legal Information Institute. Mailbox Rule Mail your acceptance Tuesday, and if the offeror tries to revoke on Wednesday before the letter lands, the contract still formed.
Then there’s consideration, which is what separates a contract from a gift. Each side has to give up something of value or take on an obligation in return for a benefit. A neighbor who promises to mow your lawn for free can sleep in without consequence. A neighbor who agreed to $50 for the job cannot. Courts rarely second-guess whether the exchange was fair; a token payment can support a contract if both sides genuinely agreed. What matters is that value moved in both directions.
Both parties also need legal capacity. Adults are presumed competent. People under 18 can enter contracts, but those contracts are voidable at the minor’s option: a teenager who signs a gym membership can walk, while the gym generally cannot. Someone with a significant cognitive impairment or someone severely intoxicated at signing may also be able to void later.
Capacity alone isn’t enough. The parties need mutual assent, sometimes called a meeting of the minds. Courts measure this objectively: based on outward words and conduct, would a reasonable observer conclude both sides agreed to the same deal?4Legal Information Institute. Mutual Assent If one person thought they were selling a 2020 sedan and the other thought they were buying a 2022 SUV, there was no mutual assent, and no contract formed.
Finally, the subject has to be legal. Agreements built around illegal activity are void from the start. A court won’t help you collect on a deal to distribute prohibited substances, no matter how carefully the terms were drafted. The same principle extends to agreements that violate public policy, including work that requires a professional license the other party doesn’t hold.
When a Contract Has to Be in Writing
Oral agreements are enforceable more often than people assume. A category called the Statute of Frauds carves out exceptions. The most common types that must be written include contracts for the sale or transfer of real estate and agreements that by their terms cannot be completed within one year.5Legal Information Institute. Statute of Frauds Under the Uniform Commercial Code, any contract for the sale of goods priced at $500 or more also needs a writing.6Legal Information Institute. Uniform Commercial Code 2-201 – Formal Requirements; Statute of Frauds
The written record doesn’t have to be a polished document. A signed receipt, an email exchange, or a text thread can satisfy the requirement, as long as it identifies the parties, describes the key terms, and is signed or otherwise authenticated by the person you’d be enforcing it against. Without some writing, these specific contracts are usually unenforceable, even if every other formation element is in place.
There’s one safety valve. Under promissory estoppel, a court can enforce an oral promise if the person making it should have reasonably expected the other side to rely on it, the other side did rely, and enforcement is the only way to avoid injustice.7OpenCasebook. Restatement Second of Contracts 90 – Promissory Estoppel It doesn’t come up every day, but when it does, it’s usually because someone made a serious financial commitment based on another person’s word.
When a Written Contract Controls Over Side Promises
Once parties put their agreement in writing and intend it as the final word, the parol evidence rule limits what outside evidence can contradict those written terms. Prior negotiations, earlier drafts, and side conversations generally can’t be introduced in court to change what the document says.8Legal Information Institute. Parol Evidence Rule The logic is straightforward: if you wrote it down and signed it, the written version controls.
Many contracts spell this out with an integration clause (sometimes called a merger clause or entire agreement clause), stating that the written document is the complete agreement and supersedes everything before it. This matters in real life. Sellers, contractors, and landlords sometimes make verbal assurances during negotiations that never land in the final contract. Once you sign a document with an integration clause, those verbal promises become extremely difficult to enforce.
There are exceptions. Courts allow outside evidence when a party was defrauded or coerced into signing, when both sides shared a mutual mistake about a key fact, or when the contract language itself is ambiguous. The baseline rule is still worth remembering: if a promise isn’t in the written contract, treat it as though it doesn’t exist.
Reasons a Contract Can Be Thrown Out
Even a contract that satisfies every formation requirement can be challenged if something went wrong in how it came together or what it contains.
Fraud and Misrepresentation
If someone lies to get you to sign, you can generally void the contract. Proving fraudulent misrepresentation means showing the other party made a false statement, knew it was false or didn’t care, intended for you to rely on it, and that you did rely and suffered harm.9Legal Information Institute. Fraudulent Misrepresentation A seller who tells you a house has a brand-new roof while knowing it leaks has committed fraud, and the sale becomes voidable at your option. A misrepresentation doesn’t have to be intentional. An honest but careless false statement about something important can also make the contract voidable if it influenced the other side’s decision to sign.
Duress
A contract signed under duress is voidable because the coerced party never truly consented.10Legal Information Institute. Duress Physical threats qualify, but economic duress is more common in contract disputes: one party threatens financial harm that leaves the other with no reasonable alternative. A vendor who refuses to deliver already-paid-for materials right before a critical deadline unless you accept a price increase may be committing economic duress, especially if you have no way to source replacements in time.
Unconscionability
Courts can refuse to enforce a contract, or strike individual clauses, if the terms are so one-sided they shock the conscience. Under UCC Section 2-302, a judge has broad discretion to throw out unconscionable provisions while keeping the rest of the agreement intact.11Legal Information Institute. Uniform Commercial Code 2-302 – Unconscionable Contract or Clause The analysis looks at both the bargaining process (whether one side was in a far weaker position, faced a take-it-or-leave-it deal, or had key terms buried in fine print) and the terms themselves (whether they impose wildly excessive costs or strip away legal rights). A contract is most vulnerable when both problems are present.
What Happens When Someone Breaks a Contract
A breach happens when one side fails to perform without a legal excuse. Sometimes it’s total, like a contractor walking off a job halfway through. Sometimes it’s partial, like a supplier delivering a week late. Either way, the non-breaching party has remedies.
Money Damages
The default remedy is money designed to put you in the position you would have been in had the contract been performed. The law calls this your expectation interest, the benefit of the bargain you lost.12Legal Information Institute. Expectation Damages Hire a painter for $2,000, watch them walk, pay $3,000 to a replacement, and your expectation damages are the $1,000 difference. Courts also recognize reliance damages (reimbursing money you spent counting on performance) and restitution (returning any benefit you already handed to the breaching party).13OpenCasebook. Restatement Second of Contracts 344 – Purposes of Remedies
Liquidated Damages
Some contracts specify in advance what a breach will cost. These liquidated damages clauses are enforceable when the agreed amount is a reasonable estimate of the harm a breach would cause, particularly where actual losses would be hard to calculate. If the amount is wildly disproportionate to any realistic harm, courts strike the clause as an unenforceable penalty. A well-drafted clause saves you from having to prove exact losses after the fact; a poorly drafted one gets thrown out when you need it most.
Specific Performance
When money can’t make you whole, a court can order the breaching party to actually perform. This remedy, called specific performance, shows up most often in real estate transactions because every piece of property is treated as unique.14Legal Information Institute. Specific Performance If a seller backs out of a deal to sell you a particular house, no amount of money perfectly replaces what you lost, so a court may order the sale to close. Specific performance is an equitable remedy, so judges have discretion, and it’s rarely available when ordinary damages would be adequate.
The Duty to Mitigate
Here’s a point that catches people off guard: once the other side breaches, you can’t sit back and let damages pile up. You have a legal obligation to take reasonable steps to minimize your losses.15Legal Information Institute. Mitigation of Damages If a tenant breaks a lease, the landlord has to make a good-faith effort to find a replacement rather than letting twelve months of rent accumulate. Failing to mitigate can reduce your recovery by whatever the court believes you could have avoided through reasonable effort. “Reasonable” is the key word. Nobody expects extraordinary measures or an obviously inferior substitute, but you can’t ignore clear opportunities to limit the harm.
How a Contract Can End Without a Breach
The simplest ending is performance. Both sides do what they promised, and the legal relationship wraps up. If parties want to end the contract early, they can agree to a mutual rescission, essentially a second agreement that cancels the first and releases both sides.16Legal Information Institute. Rescission Rescission needs its own consideration, which each party supplies by giving up their rights under the original deal.
Sometimes events outside anyone’s control make performance impossible. If the subject matter is destroyed, say a venue burns down before a scheduled event, the obligation is typically discharged.17OpenCasebook. Restatement Second of Contracts 261, 262, 265
Commercial impracticability is a narrower UCC concept. A seller may be excused from delivery when an unforeseen event makes performance impracticable, as long as the nonoccurrence of that event was a basic assumption underlying the contract.18Legal Information Institute. Uniform Commercial Code 2-615 – Excuse by Failure of Presupposed Conditions A government embargo cutting off a supplier’s only source of raw materials could qualify. Rising costs, market shifts, or a deal that turned less profitable than expected will not. If performance is still technically possible but just more expensive, that’s a business loss, not impracticability.
Frustration of purpose covers a different scenario. Performance is still possible, but the reason you entered the contract has evaporated. The classic example is renting a hotel room overlooking a parade route after the parade gets canceled. The room is still available; the point of renting it isn’t. For the defense to work, the frustrated purpose must have been central to the deal, and the frustrating event must not have been the claiming party’s fault.17OpenCasebook. Restatement Second of Contracts 261, 262, 265
A contract can also end before performance is even due. When one party clearly communicates they won’t perform, the other side doesn’t have to wait for the deadline. This is anticipatory repudiation, and it gives the non-breaching party an immediate claim. You can treat the contract as broken, stop your own performance, and pursue damages right away. Waiting usually isn’t smart anyway, because the duty to mitigate kicks in immediately.
How Long You Have to Sue
Even a clear breach doesn’t give you forever to file. Every state sets its own deadline, and the clock generally starts from the date of the breach. For written contracts, the filing window typically runs somewhere between four and ten years depending on the state. Oral contracts usually have shorter deadlines, often between two and six years. Miss the deadline and you lose the right to sue entirely, regardless of how strong the claim was. If you think someone has breached a contract with you, checking your state’s deadline early is one of the simplest ways to protect yourself.