The Claims Interpreted Report

When Are Preambles Limiting?

In his recent article Without Preamble, Stanford professor Mark Lemley surveys the morass of law on determining when patent claim preambles are limiting, and he predicts that it will be swept away if the Supreme Court ever faces the issue. Given that possibility, how should practitioners think about drafting preambles when applying for a patent?

Much of legal academic literature provides little use for practitioners, instead proposing grand constitutional theories, doing social science on legal institutions, or setting out policy arguments for changing the law. Professor Lemley’s article falls under the more useful category of doctrinal analysis: surveying a field of law and offering some original points that practitioners would do well to think about.

The field of law in this article is claim construction when applied to the preamble of the claim. The preamble is the introduction to a patent claim, typically followed by a transition term like “comprising” or “consisting of” and then the body of the claim. The body recites the substantive limitations making up the invention. By default, the preamble is not limiting, meaning that it is given no weight in anticipation, obviousness, or infringement. A prior art reference can anticipate a claim even if what is in the preamble is not in that reference, and an accused product can infringe a claim even if the product does not match what is in the preamble.

But that’s only the default rule. Courts have found many situations in which the preamble will be limiting:

Courts have also found that the preamble is not limiting if the body of the claim is “structurally complete,” typically meaning that the preamble only provides a purpose, use, benefit, context, or so on. But an exception occurs if ignoring the preamble would make the claim “divorced from reality.”

None of these rules are applied consistently. “The result is that it is impossible to predict with confidence whether the words of the preamble will actually be treated as part of the claim.” For example, the preamble “for treating a cancer patient to effect regression of a taxol-sensitive tumor” was found not limiting, and the preamble “for diagnosing an increased risk for thrombosis” was found limiting.

This body of law consists of Federal Circuit and district court cases; the Supreme Court has not weighed in on interpreting preambles. Professor Lemley predicts that, when the Court sooner or later addresses the issue, the Court will simply eliminate the special rule that preambles are not necessarily limiting. In the last couple decades, the Court has swept away several patent-specific rules in favor of general principles of law. For claim construction, statutory interpretation and contract interpretation provide those general principles. In those contexts, the principle is that every word of the statute or contract matters for the interpretation, and the Court will likely apply that principle to preambles.

Lessons for Practice

If the Supreme Court eventually rules as Professor Lemley predicts, the ruling would be retroactive: it would apply to all patents currently in force, not just patents issued from that time forward. This creates some uncertainty around the status of the preamble. “[P]atent owners interested in certainty might consider not writing preambles. If they do, they should understand that those preambles might not be limiting now but likely will be in the not-too-distant future and that the patentee will have no control over whether and when that will happen.” Even if one does not share Professor Lemley’s prediction about how the Supreme Court would rule, the current state of the law generates much the same uncertainty.

I think a useful strategy is to draft preambles to say as little as possible, trying to leave little daylight between limiting and nonlimiting interpretations of the preamble. For example, if the body of the claim recites a sensor and surrounding components, then the preamble could be “a sensor apparatus.” One could take this a step further (following a proposal Professor Lemley has for the Patent Office) and only use the statutory categories listed in 35 U.S.C. § 101: “a process,” “a machine,” “a manufacture,” or “a composition of matter.” In any event, when drafting preambles, practitioners should consider how the claim fares when the preamble is limiting and when it isn’t.

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