Defending Against an Allegation of Non-Performance
When a creditor tells a debtor that the contract has been breached, the debtor's position is not empty: the Civil Code provides several real lines of defence against an allegation of non-performance. These lines are the concept of delay of performance and its limits, non-fault impossibility, adaptation of the contract to changed circumstances, and the rules limiting recoverable damage. Each is a separate construction, and their correct application either dissolves the allegation or limits its volume.
The Concept of Delay and Its Limits
The first line is conceptual: the allegation moves on the terrain of time, and the concept must be applied precisely. Under Article 400 of the Civil Code, delay of performance by the debtor exists where the obligation is not performed at the time established for performance, or where after the arrival of the performance term it does not perform the obligation even after a warning by the creditor. But the frame has an exception: under Article 401 of the Civil Code, the term is not deemed exceeded where the obligation was not performed due to circumstances not caused by the debtor's fault. These two norms together pose the question whether the delay was culpable, and the answer decides the whole architecture of the defence.
Changed Circumstances and Adaptation of the Contract
The second line is situational. Under Article 398 of the Civil Code, where the circumstances that became the basis of the conclusion of the contract have evidently changed after its conclusion, and the parties would not have concluded the contract, or would have concluded it with different content, had these changes been taken into account, adaptation of the contract to the changed circumstances may be demanded. Otherwise, considering individual circumstances, a party to the contract cannot be required to adhere strictly to the unaltered contract. A change of circumstances is also equated with the case where the notions that became the basis of the contract prove incorrect. The same norm contains the procedural rule of defence: the parties must first attempt to adapt the contract to the changed circumstances, and if that is impossible or the other party does not agree, the party whose interests were harmed retains the right to refuse the contract.

