Patent validity and patent enforceability are often confused. Patent validity refers to whether the patent meets the statutory requirements for patentability, enumerated in the Patent Laws, 35 U.S.C. § 101 et seq. The Patent Laws specify the subject matter for which a patent may be obtained and the conditions for patentability. For example, to be patentable, a claimed invention must be useful, novel and not obvious. If claimed subject matter fails to meet any of the requirements for patentability, the patent is not valid.
Patent enforceability, on the other hand, refers to situations where a patent may not be enforceable due to equitable reasons. For example, a patent applicant has a Duty of Candor owed to the USPTO, requiring that the applicant disclose prior art to the USPTO that the applicant is aware of that is material to the patentability of the patent claims he seeks. If the patentee violates this Duty of Candor and withholds material information, the patent may be unenforceable. It is possible to have a valid patent that is unenforceable.