Validity and effectiveness have similar meanings, but are used in very different situations. Something is valid if it is well-grounded and justifiable or is acceptable. While something is effective if it has the power to produce some sort of effect.
Both validity and effectivenss describe the extent to which a contract is capable of reaching the desired legal effect.
Validity: The status of a contract which conforms to all requirements, and there is no reason for its invalidity.
Effectiveness: Effectiveness determines the scope that a legal norm or a contract is intended to cover in terms of time, persons and/or territorial extent.
