Which of the following can be a basis for forming a contract?

The basis for forming a contract lies in the mutual agreement and promises made between two or more parties. A contract is fundamentally a legally binding agreement that requires at least two parties to have a mutual understanding and acknowledgment of their obligations and rights. This means that both parties must agree to the terms of the contract, indicating a consensus that is essential for the establishment of a contractual relationship.

Written promises can serve as evidence of a contract but are not the sole basis for forming one; contracts can also be verbal. A single party's intention, while important, is not sufficient on its own to create a contract because a contract requires the consent and promises of at least one other party. Likewise, an oral agreement that lacks meaningful consequences does not constitute a genuine contract, as enforceability and intention are key components of a contract's validity.

Therefore, the notion of promises and agreements between two or more parties encapsulates the essence of contract formation, making it the correct and comprehensive choice.