Under U.S. Law, using both invalid and unenforceable is redundant. An invalid provision of a contract is unenforceable. Likewise, and unenforceable provision of a contract is invalid. Here are the definitions of the two from Black's Law Dictionary. (10th. ed. 2014) defines them as follows:
Unenforceable Contract - An otherwise valid contract that,
because of some technical defect, cannot be fully enforced; a contract
that has some legal consequences but that may not be enforced in an
action for damages or specific performance in the face of certain
defenses, such as the statute of frauds.
Invalid Contract - An agreement that is either void or voidable.
Also, be aware that invalid and unenforceable are different than void and voidable contracts. These terms often get confused.
Again, looking to Black's Law dictionary,
Void Contract 1. A contract that is of no legal effect, so that there is really no contract in existence at all. • A contract may be
void because it is technically defective, contrary to public policy,
or illegal. — Also termed void agreement. Cf. illegal contract;
unenforceable contract; voidable contract.
Strictly speaking, a "void contract" is a contradiction in terms. Void contract describes a situation where despite the intention of the parties, no contract has been made.
Voidable Contract - A contract that can be affirmed or rejected at the option of one of the parties; a contract that is void as to the
wrongdoer but not void as to the party wronged, unless that party
elects to treat it as void. — Also termed voidable agreement.
“A voidable contract is a contract which, in its inception, is
valid and capable of producing the results of a valid contract, but
which may be ‘avoided,’ i.e. rendered void at the option of one (or
even, though rarely, of both) of the parties.” P.S. Atiyah, An
Introduction to the Law of Contract 37–38 (3d ed. 1981).
So, to summarize:
- Invalid = Unenforceable
- Unenforceable = Invalid
- Void and voidable are entirely different