Certain defenses to a claim of patent infringement produce, if successful, a holding that the patent is unenforceable rather than invalid. The most important of these are the inequitable conduct and misuse defenses.1 If a patent is unenforceable, it cannot be the basis of an infringement claim.
In a court proceeding, the presence of an adversary helps to keep the litigants honest. If one party shades the truth or withholds important evidence from the court, the other party will expose the error, if it can. As discussed in Section 5.1, patent prosecution is ex parte, meaning that persons who might oppose the issuance of a patent have no opportunity to participate. If the applicant misrepresents the facts, there is no one to contradict him. Moreover, the Patent Office often relies heavily on information provided by the applicant. The applicant's s sales activities, for example, might be enough to raise a statutory bar under 35 U.S.C. § 102(b),2 but the patent examiner generally knows about those activities only what the applicant chooses to tell. Nevertheless, every issued patent enjoys a presumption of validity.
Because an applicant could take unfair advantage of this situation, applicants are charged with a duty of candor more demanding than what
1 Another unenforceability defense might be raised where ownership of a patent subject to a
terminal disclaimer had been transferred, contrary to the requirement that patents linked by
a terminal disclaimer remain commonly owned. See Section 8.12.
2See Section 8.10.1.