Which of the following actions constitutes a breach of contract?

Failing to perform contractual obligations as agreed is the hallmark of a breach of contract. A contract is a legally binding agreement that outlines specific duties and responsibilities that each party must fulfill. When one party does not meet these obligations as specified in the contract, it results in a breach. This could occur due to various reasons, such as when a party simply refuses to perform, delivers substandard goods or services, or fails to meet deadlines.

In contrast, accepting new terms typically signifies that both parties are in agreement to modify their original terms, which does not imply a breach but rather a potential renegotiation of the contract. Negotiating contract details is a process that often occurs before a contract is finalized and does not constitute a breach since it is part of creating or amending the agreement. Transferring contract rights to a third party, known as assignment, may or may not breach a contract depending on the original terms; many contracts allow assignment unless specific conditions prohibit it. Thus, the correct understanding revolves around the clear responsibilities outlined in the contract and the consequences of failing to fulfill those duties, which highlights why failing to perform contractual obligations is defined as a breach.