Answer
Under Article 1318 of the Civil Code, there is no contract unless three essential requisites concur: (1) the consent of the contracting parties; (2) a determinate object which is the subject matter of the contract; and (3) a cause (or consideration) of the obligation which is established. If any one of these is absent, no valid contract arises.
Contracts with certain defects fall into four kinds: rescissible (valid but may be set aside for economic injury or fraud on creditors), voidable (valid until annulled because consent was vitiated or a party was incapacitated), unenforceable (valid but not judicially enforceable unless ratified, as under the Statute of Frauds), and void or inexistent (producing no effect from the beginning and incapable of ratification).