Explanation:

- Option 1: State

Some rights and duties are established by state laws, especially those related to public policy and regulatory requirements. However, these are not typically direct contractual rights.

- Option 2: Statute

Statutes can impose obligations or confer rights that affect contracts, such as the Sale of Goods Act. Yet, they do not directly create contractual rights and duties; they mainly govern them.

- Option 3: Parties

Contractual rights and duties are primarily created by the parties involved. They agree upon terms, obligations, and rights, forming the basis of the contract.

- Option 4: Custom or Usage

Custom or usage may influence the interpretation of a contract but doesn't directly create rights and duties unless incorporated into the terms by the parties.