We’re far from it. In fact, you’ve likely entered dozens of valid contracts today alone—buying coffee, using an app, agreeing to terms on a website. And yet, only a fraction rise to the level of dispute. So what separates a real contract from a casual promise? Let’s unpack it.
Express Contracts: When Words Create Binding Obligations
An express contract is what most of us picture—clear, direct terms stated aloud or in writing. “I’ll pay $500 for your laptop.” “You deliver by Friday, I wire the funds by noon.” These are explicit promises, deliberately exchanged. No guessing. No reading between the lines. The agreement is on the surface, often documented, sometimes not. But clarity is key.
Express contracts dominate business transactions. They’re behind every SaaS subscription (yes, even that $9.99 monthly tool you forgot about), every freelance gig on Upwork, every real estate closing. Because the terms are spelled out, disputes usually hinge on interpretation, not existence. Courts look at language, context, and intent—what did Party A actually say, and did Party B reasonably understand it that way?
Here’s where it gets tricky: an express contract doesn’t need to be formal. A text message saying “Sold you the bike for $200, cash on pickup” may be fully enforceable. In 2021, a Florida court upheld a real estate deal based on a single emoji—a handshake —sent via iMessage. Yes, really. That’s how much weight modern courts give to digital intent.
And that’s exactly where the myth of “it’s not official unless it’s notarized” falls apart. Notarization adds verification, not validity. The law cares about consent and clarity, not ceremony. So if your landlord texts, “Rent is $1,200, due the 1st,” and you reply “Got it,” you’ve just formed an express contract.
Written vs. Oral Express Contracts: Does Format Matter?
Some contracts must be in writing under the Statute of Frauds—like real estate sales, agreements lasting over a year, or promises over $500 in many states. But outside those categories? Oral contracts are legally binding. A handshake deal for roofing repairs? Enforceable. A verbal promise to lend $3,000? Yes, if proven.
But—and this is a big but—proving an oral agreement is another story. Memory fades. Witnesses disappear. That’s why written records rule. Emails, texts, even WhatsApp threads are now routinely admitted as evidence. In small claims courts across California, over 60% of successful claims rely on digital messages as proof of contract.
Express Terms vs. Implied Warranties: Where the Lines Blur
Express terms are what you say. Implied warranties are what the law assumes you meant. Buy a toaster, and you’re not told it’ll last a year—but the law says it should work for a reasonable time. That’s not part of the express contract. It’s layered underneath. And manufacturers hate when you bring that up in disputes.
Implied Contracts: When Silence Still Binds You
Now we enter murkier territory. An implied contract isn’t spoken or written. It’s inferred from behavior. You walk into a restaurant, sit down, order a steak. You never said “I promise to pay” aloud. But your actions? They scream it. The law sees this as a mutual understanding: service rendered, payment expected.
Implied contracts live in everyday life. When your neighbor’s dog digs up your lawn and you spend $180 fixing it, then hand them a bill, a court might say, “Yes, they should’ve paid.” Why? Because you didn’t expect to do free landscaping. And they knew it. It’s not charity. It’s an implied-in-fact contract—formed by conduct, not conversation.
But not all silence counts. The key is mutual intent. Did both parties act as if an agreement existed? In a 2017 New York case, a man regularly mowed his neighbor’s lawn for three years without being asked. Then he invoiced $4,200. Denied. Why? No evidence the neighbor accepted or expected the service. That’s the difference between kindness and contract.
And here’s a twist: some implied contracts are created by law, not behavior. These are implied-in-law contracts, also called quasi-contracts. They’re not real agreements. They’re legal fictions courts use to prevent injustice. Someone accidentally pays you $10,000? You keep it? Nope. The court may order repayment—not because you agreed, but because it would be unfair to profit from a mistake. We call it restitution. It’s a backdoor fix, not a true contract, but the outcome feels the same.
Unilateral Contracts: One Promise, One Performance
This one trips people up. A unilateral contract isn’t a two-way street. It’s a one-way offer: “I’ll pay $500 to anyone who finds my lost dog.” No one has to accept. But if someone does the act—finds the dog—they’ve accepted by performance. The reward must be paid.
Unilateral contracts are common in incentives: reward posters, contest prizes, bug bounties in tech. Google paid a 19-year-old $17,000 in 2020 for finding a flaw in Chrome. He didn’t sign anything. He just fixed it. That’s unilateral. The offer was public. The performance was the acceptance.
Here’s where people get confused: you can’t partially perform and demand payment. You didn’t “almost” find the dog? Sorry. You either completed the task or you didn’t. This differs sharply from bilateral contracts, where ongoing obligations exist. And that’s exactly where businesses mess up—offering rewards without clear endpoints, then refusing to pay when someone delivers.
The Legal Trigger: When Does Acceptance Happen?
In bilateral deals, acceptance is a “yes”—a signature, a call, a nod. In unilateral? It’s action. No need to notify the offeror beforehand. You could find that dog while they’re asleep, then show up at 3 a.m. with proof. The obligation kicks in retroactively. Courts have upheld this even when the finder didn’t know about the reward—though that’s rare. Usually, knowledge of the offer is required.
Bilateral Contracts: The Backbone of Modern Commerce
If unilateral contracts are niche, bilateral ones dominate. These are two-way promises: “I’ll pay you $5,000 if you design my website by June 30.” Both sides commit. Both are bound. This is your employment contract, your mortgage, your Netflix subscription. Reciprocity is the engine.
Bilateral agreements are easier to enforce because obligations are mutual and often ongoing. Breach by one party lets the other walk away—or sue. A freelancer ghosts a client after two weeks? The client can withhold payment. The freelancer demands full pay? Tough. They didn’t fulfill their end.
What’s underappreciated is how many bilateral contracts are formed daily without paperwork. You sign up for a gym, give your card, and agree to auto-renew. That’s a binding bilateral contract. Canceling isn’t always easy—some gyms in Texas have sued members for trying to leave early. And won. Because you clicked “agree.”
Because digital consent is so frictionless, people don’t realize they’ve signed anything. But the law sees it differently. In 2022, a survey found that 78% of users skip reading terms of service entirely. Yet those terms still bind them. That’s not conspiracy. It’s contract law.
Express vs. Implied vs. Unilateral vs. Bilateral: The Real Differences
Let’s map this out. Express and implied are about how the contract is formed—words or actions. Unilateral and bilateral are about structure—single promise vs. mutual exchange. You can have an express unilateral contract (“I’ll pay $1,000 to the first person to swim the English Channel this year”) or an implied bilateral one (your long-time plumber shows up monthly, you pay without discussing terms—routine creates obligation).
The confusion often lies in overlap. A freelance job might start as a verbal express bilateral agreement, then evolve into an implied ongoing one after years of work. Courts look at continuity, not labels. And that’s exactly where small businesses lose—assuming informality means freedom from liability.
To give a sense of scale: over 90% of commercial contracts are bilateral and express. But in personal or emergency contexts—medical care, emergency repairs, spontaneous services—implied and unilateral deals rise sharply. A doctor treating an unconscious patient? No signed form. But the family may still be billed. An implied-in-law obligation kicks in.
Frequently Asked Questions
Can a text message be a valid contract?
Absolutely. If the message contains offer, acceptance, and consideration (something of value exchanged), it’s binding. Courts have upheld agreements based on SMS, iMessage, even Facebook Messenger. The medium doesn’t matter—intent does. Just don’t rely on emojis alone unless you’re feeling lucky.
Do all contracts need to be in writing?
No. But some must be, under the Statute of Frauds. These include real estate transfers, marriage agreements, and contracts that can’t be fulfilled within one year. For everything else? Verbal or digital can work. But proving them is harder. Suffice to say: write it down.
What makes a contract invalid?
Several things. Lack of capacity (minors, mentally impaired), coercion, fraud, or illegal purpose. A contract to sell stolen goods? Void. One signed under duress? Unenforceable. Also, if terms are too vague—“I’ll pay you later”—courts may say no meeting of the minds occurred. Precision matters.
The Bottom Line
The four real contracts—express, implied, unilateral, bilateral—are not abstract legal theory. They’re operating beneath every transaction you make. The problem is, most people only notice them when something goes wrong. I find this overrated idea that “real contracts” require pen and paper. It’s outdated. We live in a world of taps, clicks, and gestures. The law has adapted. Have you?
Takeaway? Assume you’re bound more often than you think. And when in doubt, get it in writing. Not because it’s required—but because memory is flawed, and courts love paper trails. Honestly, it is unclear how long digital-only agreements will hold up under mass scrutiny. But for now, a text is enough.
Because the law isn’t about perfection. It’s about fairness. And sometimes, fairness means you pay for that steak dinner you never verbally agreed to.