The term ‘constructive or quasi contract is a misnomer, the cases grouped under this type of contracts have little or affinity with contract. Such a contract does not arise by virtue of any agreement, express or implied between the parties but the law infers or recognizes a contract under certain special circumstances. For example, obligation to finder of lost goods to return
them to the true owner or liability or person to whom money is paid under mistake to repay it back cannot be said to arise out of a consent, but these are very much conversed under quasi contracts as per sections 71 and 72 respectively. The contract act has rightly named such contracts as “certain relations resembling those created by contract”.

A quasi contract is based upon the equitable principle that a person shall not be allowed to retain unjust benefit at the expense of another. Sections 68-72 of the contract act describe the cases which are to be deemed ‘quasi contracts’.

Example:

A says to B, If you dig my garden next Sunday, I will pay you Rs. 500.’ B makes no commitment, but says, I am not sure that I shall be able to, but if I do, I shall be happy to take Rs. 500. This arrangement is not bilateral. A has committed himself to pay Rs. 500 in certain circumstances, but B has made no commitment at all. He is totally free to decide whether he wants to dig A’s garden or not. If B does not turn up on Sunday to dig the garden, A cannot do anything about is. If, however, B reaches to A’s place on Sunday to do the work, it will amount to his acceptance a contract will be formed where both parties will be bound by their performance.