An express contract is formed by written or oral language.
An implied-in-fact contract is manifested by the actions of the parties, although it is not explicitly written or stated. Example: plunking down 50 cents at a newsstand and taking a paper.
A quasi-contract is a recovery or obligation that is not created by an actual agreement, but by the law for “reasons of justice.” It is not an actual contract negotiated by the parties. Example: A plumber walks by a home and fixes a burst pipe that was flooding the basement while the homeowner was absent. The plumber may be able to recover in quasi-contract, notwithstanding the absence of an actual agreement with the owner to perform the service and receive compensation.
1. Bilateral Contract
A bilateral contract is formed by mutual exchange of promises by the contracting parties. Example: A promises B that he will sell B ten baseball cards, and B promises to pay A one dollar.
2. Unilateral Contract
A unilateral contract is one in which a promise is made in exchange for actual performance, as opposed to a promise to perform.
Example: A promises to pay B $100 if B paints A’s home. A has not asked B for a promise to paint, but rather to actually paint.
3. Distinction Between Unilateral and Bilateral
Contracts The difference between unilateral and bilateral contracts is not as important today as in the past. However, one significant difference is the extent of the obligations they impose. Once parties exchange promises in bilateral contracts, they are obligated to perform their promises. In a unilateral contract, the nonpromising party is not obligated to perform and the promisor’s obligation does not arise until the requested act is completed.