i. Essential Elements of a Valid Contract:

1. Offer: A clear proposal made by one party to another intending to create a legal obligation upon acceptance.
2. Acceptance: The unqualified agreement to the terms of the offer, creating a binding contract.
3. Consideration: Something of value exchanged between the parties, which can be in the form of money, services, or goods.
4. Legal Capacity: Both parties must have the legal ability to enter into a contract, meaning they are of sound mind, not minors, and not disqualified from contracting by law.

ii. Rules Guiding Consideration in a Contract:

1. Consideration Must Move from the Promisee: The party who is entitled to enforce the contract must provide consideration.
2. Consideration Must Be Sufficient but Need Not Be Adequate: The law does not require the consideration to match in value, but it must have some value.
3. Consideration Must Not Be Illegal or Immoral: Any consideration that involves illegal activities or violates public policy is unenforceable.
4. Consideration Must Be Definite: The terms of the consideration must be clear and not vague or ambiguous.