Discharge of contract by impossibility of performance

If an agreement contains an undertaking to perform an impossibility, it is void ab initio. This rule is based on the following maxims:

1. Impossibility existing of the time of agreement: Sec. 56 lays down that can agreement to do an impossible act itself is void”. This is known as pre-contractual or initial impossibility.
2. Impossibility arising subsequent to the formation of contract:  Impossibility which arises subsequent to the formation of a contract (which could be performed at the time when the contract was entered into) is called post-contractual or supervening impossibility.