Whether § 112 requires a patent's specification to contain a written description of all of the limitations of a patent's claims, not just a 'substantially equivalent' disclosure

QUESTION PRESENTED Under 35 U.S.C. § 112, a patent’s specification must “contain a written description of the invention.” That requirement, a cornerstone of federal patent law, ensures that an inventor can claim patent protection only for what she actually invented. Consistent with this Court’s longstanding directive that every element of a patent claim must be treated as material, the Federal Circuit has long held that all elements of a patent’s claims must actually be disclosed in the patent’s specification. But the Federal Circuit has now broken from that established rule. In the 2-1 decision below, the Federal Circuit announced for the first time that for some claim limitations, a “substantially equivalent” disclosure will do. Here, although the claims expressly require testing using one specific method identified by name, the court held that the written description’s disclosure of a different testing method was good enough. The court grounded its change of heart not in statutory text or precedent, but in the court’s view that “[r]igidity should yield to flexible, sensible interpretation.” The question presented is: Whether § 112 requires a patent’s specification to contain a written description of all of the limitations of a patent’s claims, not just a “substantially equivalent” disclosure. i