Choose the correct word in each pair to complete the text.

A promise to perform

We should distinguish between two types of promise, namely those which do and don't give rise to a legal duty . Thus, a promise to meet one's other half for dinner at 7pm gives rise to no legal obligation - it is a "mere" promise - whereas a promise to sell someone a car for £5000 gives rise to legal obligation .

English contract doctrine distinguishes between bilateral and unilateral contracts. A bilateral unilateral (1 p.) contract gives rise to obligations on both sides. Thus in a contract of sale, the seller has an obligation to transfer title in the thing sold to the buyer, whilst the buyer has an obligation to pay the price. A bilateral unilateral (1 p.) contract, by contrast, gives rise to obligations on one side only. Thus "I will give you £100 if you run a marathon" gives rise to a legal duty on the promisee promisor (1 p.) to pay the money if the race is run, whilst the person to whom the offer is made (the promisee promisor (1 p.) ) is under no obligation to run in the first place.