A bilateral contract is distinguished from a unilateral contract in that a bilateral contract involves:

Giải thích

A bilateral contract is formed by an exchange of promises: both sides are bound the moment the promises are exchanged, and each promise is the consideration for the other. Almost every construction contract is bilateral — the contractor promises to build, the owner promises to pay. (d) is the unilateral contract, where the offer asks for a completed act rather than a promise, so nothing binds the offeree until he performs and the act is both acceptance and performance (Civil Code §1584). (c) describes that same unilateral arrangement from the offeror's side, which is why it reads plausibly. (a) removes the element Civil Code §1550 makes essential; a promise without consideration is not a kind of contract but a failed one.