unilateral contract
Unilateral Contract is a promise that only one side makes, and it only becomes binding when someone else does the thing being asked, not before.
In plain English
Here is the strange part. In most contracts, both sides sign something before anyone moves. In a unilateral contract, nobody signs anything at the start, and yet the promise is already binding the moment it is made. It is the one deal where the paperwork can wait but the money cannot.
Think of the man in Lagos who pastes a notice outside his shop, ₦50,000 to whoever finds his stolen generator and returns it. He has not signed anything with anybody. He does not even know who will show up. But the moment somebody actually finds that generator and brings it back, he owes them the ₦50,000, no argument, no need for a handshake beforehand. His promise was open to the whole world, and one person closed the loop by acting on it.
This is different from the usual business contract where two people negotiate, agree on terms, then both sign. Here, there is only one promise, sitting out there waiting. The other person is never obligated to respond. But if they choose to act, the promise snaps shut around them and becomes enforceable.
A common United Kingdom example is a reward poster for a lost dog, or an insurance company that publicly promises to pay out if a specific rare event happens, like a bank offering cashback if you complete certain transactions in a month. Nobody forces you to do the transactions, but if you do, the bank must pay.
Entrepreneurs use this more than they realise. A startup founder who announces, anyone who refers a paying customer gets ₦10,000, has created a unilateral contract with every single person who reads that post. No form to fill first. The referral itself is the acceptance.
A Lagos landlord announces, ₦20,000 to whoever paints my shop front by Friday. A painter shows up and finishes the job by Thursday evening. The landlord now owes exactly ₦20,000, even though the painter never signed anything before starting the work.
Questions people ask
Can the person who made the promise cancel it before someone finishes the task?
Generally yes, before performance is complete, but many courts and reasonable practice say once someone has clearly started acting on the promise in good faith, the promiser cannot cancel and walk away without consequence.
How is this different from a normal business contract?
A normal contract needs agreement from both sides before it becomes binding, usually through signatures or clear mutual acceptance. A unilateral contract only needs one side to promise, and it becomes binding the moment the other side actually performs the requested act.
Do unilateral contracts need to be in writing to count?
Not always. A spoken announcement or a public notice can create a binding unilateral contract, though having it written down makes it far easier to prove later if there is any dispute about what was promised.
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