The legality of the object and consideration are two essential elements in contract law that determine the validity of a contract:

1. Legality of Object:

   - The legality of the object refers to the requirement that the purpose or subject matter of a contract must be lawful. In other words, the contract cannot involve activities or objectives that are prohibited by law or against public policy.

   - Contracts with illegal objects are generally void and unenforceable. For example, a contract to engage in illegal drug trafficking or commit a crime would be considered illegal and unenforceable.

2. Consideration:

   - Consideration, as mentioned previously, is something of value exchanged between parties in a contract. It's a fundamental element that shows that the parties are making a fair exchange and that they intend to create a legally binding agreement.

   - To be valid, consideration must be legal. This means that what is being exchanged must not involve illegal activities or actions contrary to public policy.

   - If the consideration in a contract is illegal, it can render the entire contract unenforceable. For example, a contract that promises payment in exchange for illegal gambling winnings would likely be void due to the illegal consideration.

In summary, both the legality of the object and the consideration must be legal for a contract to be valid and enforceable. Contracts with illegal objects or illegal consideration are generally void and cannot be upheld in a court of law. It's essential for parties entering into contracts to ensure that the purpose and consideration are in compliance with the law and public policy to avoid legal complications.