1. Core Legal Answer & Context: The statement "An agreement to do an act impossible in itself is void" is the first paragraph of Section 56 of the Indian Contract Act, 1872. This part deals with initial impossibility, meaning if an agreement is impossible to perform from the very beginning, it is void.

Doctrine of Frustration (Subsequent Impossibility): The second paragraph of Section 56 embodies the 'doctrine of frustration'. This doctrine applies when a contract, which was valid and capable of performance at the time of its formation, subsequently becomes impossible to perform or unlawful due to an event beyond the control of the parties. In such circumstances, the contract becomes void, and the parties are discharged from their obligations. The underlying principle is that the law will not compel a party to perform an act that has become impossible or fundamentally altered.

Specific Grounds of Frustration (as interpreted by courts):

• Destruction of the Subject-Matter: If the specific thing or person essential for the performance of the contract is destroyed or ceases to exist (e.g., a hall booked for an event burns down).
• Change in Law: If a subsequent legislative or administrative act makes the performance of the contract unlawful or illegal (e.g., a ban on the trade of certain goods).
• Failure of Ultimate Purpose: If the very object or purpose for which the contract was entered into is defeated by an unforeseen event, even if physical performance is still possible (e.g., hiring a room to watch a procession that is subsequently cancelled).
• Death or Incapacity of a Party: In contracts requiring personal skill or service, the death or incapacitation of the party whose performance is essential frustrates the contract.
• Outbreak of War: If the outbreak of war makes performance impossible, illegal, or radically different from what was contemplated (e.g., contract with an alien enemy).
• Non-occurrence of a Contemplated Event: If an event, which was the basis of the contract, does not occur, and its non-occurrence makes the performance of the contract pointless.

2. Relevant Statutes and Sections: Section 56 of the Indian Contract Act, 1872.

3. Important Landmark Cases:

• Satyabrata Ghose v. Mugneeram Bangur & Co.: This is the locus classicus on the doctrine of frustration in India. The Supreme Court held that Section 56 is exhaustive and covers both initial and subsequent impossibility. It clarified that 'impossible' does not mean merely physical or literal impossibility, but also includes impracticality or uselessness from the object and purpose of the parties.
• Ganga Saran v. Firm Ram Charan Ram Gopal: Reaffirmed the principles laid down in Satyabrata Ghose, emphasizing that the impossibility must be supervening and not self-induced.

4. Clear Conclusion: Section 56 of the Indian Contract Act voids agreements impossible from the outset and also incorporates the doctrine of frustration, which discharges parties from contractual obligations when performance becomes impossible or unlawful due to unforeseen supervening events. This doctrine ensures fairness by releasing parties from contracts whose fundamental basis has been destroyed, preventing undue hardship.