How US patent claims should be interpreted has been the subject of intense debate, and has been considered by the US Supreme Court three times since 1996. Following the recent decision of the Supreme Court in Festo Corporation v Shoketsu Kinzoku1 the rules have hopefully now become more settled. The decisions in the above three cases should be considered together, and the purpose of this article is to summarise the main points that can be gleaned from them and to consider their implications for European practitioners in their day-to-day work of drafting applications and providing instructions to their colleagues in the USA. Of course, where there is any difficulty, or where a legal opinion is required, there is no substitute for the advice of a US practitioner.
At issue in Markman2 was whether the construction of a patent, including terms of art within the claims was for the court to decide, or whether it should be decided by a jury, the right to a jury trial in any action where the value in dispute exceeds $20 being preserved by US Constitution, seventh amendment. The Court decided that the construction of patents, as of other written documents, should be left to the judge since common law practice at the time of framing of the US Constitution and early cases from England both showed that judges, not juries, construed terms in patent specifications, and because this which a task that a judge, from his training and discipline, was in the better position to perform. Following that decision, pre-trial Markman hearings to construe the patent's claims following motions by defendants for summary judgment have become a routine feature of infringement trials and now account for a major part of the work of the CAFC3.
The continued existence of the doctrine of equivalents was challenged in both Warner Jenkinson v Hilton Davis4 and in Festo. In both cases it was held not to have been rendered obsolete by the entry into force of 35 USC 103 in 1952. In Festo the Court explained that:
The language in the patent claims may not capture every nuance of the invention or describe with complete precision the range of its novelty. If patents were always interpreted by their literal terms, their value would be greatly diminished. Unimportant and insubstantial substitutes for certain elements could defeat the patent, and its value to inventors could be destroyed by simple acts of copying. For this reason, the clearest rule of patent interpretation, literalism, may conserve judicial resources but is not necessarily the most efficient rule. The scope of a patent is not limited to its literal terms but instead embraces all equivalents to the claims described. See Winans v. Denmead, 15 How. 330, 347 (1854).
It is true that the doctrine of equivalents renders the scope of patents less certain. It may be difficult to determine what is, or is not, an equivalent to a particular element of an invention. If competitors cannot be certain about a patent's extent, they may be deterred from engaging in legitimate manufactures outside its limits, or they may invest by mistake in competing products that the patent...