Which of the following is NOT a requirement of a valid contract?

A valid contract typically requires several essential elements, one of which is mutual agreement, often referred to as a "meeting of the minds," where all parties involved understand and agree to the terms of the contract. Additionally, the parties must have the capacity to contract, meaning they are legally able to enter into a binding agreement, and there must be consideration, which is a value exchanged between the parties.

Proper witness signatures are not universally necessary for a contract to be valid, except in specific situations prescribed by certain laws, such as when dealing with real estate transactions or formal wills. In many instances, contracts can be enforceable without the need for witnesses. Thus, while witness signatures may enhance the proof of the contract's legitimacy, they are not a fundamental requirement for contract validity compared to mutual agreement, capacity, and consideration, which are standard legal prerequisites.