Professor Mark Lemley's article Without Preamble (2019-2020) relates to the topic of claim construction, which can determine the outcome of patent litigation.
As background, a US patent claim has three parts: (1) a preamble, which states what the invention is or its environment, (2) a transitional term (e.g., comprising), and (3) a body that lists the steps of a method or the structure of a system. Generally, courts hold a preamble is a claim limitation "if it gives life, meaning and vitality" to the claim or recites essential structure or steps. Yes, it's a case by case determination. Perhaps a more practical test is whether the preamble is referenced repeatedly in the body. If so, the preamble is a claim limitation, i.e., for purpose of determining validity and infringement. See Mueller, Patent Law (2020).
Turning to Professor Lemley's Abstract:
"The Federal Circuit is ignoring a significant share of the words of patent claims. That's a bad idea as a matter of policy. It is virtually impossible to tell when the court is going to do it. And it’s inconsistent with the idea that the claims define the scope of the invention, and with how the Supreme Court thinks about claim construction and its closest analogies, statutory interpretation and construing contracts.
The culprit is a labyrinthine set of rules the Federal Circuit uses to decide whether or not to include the 'preamble' to a patent claim as a part of the claim. The words of the preamble, which can sometimes amount to more than half of the whole claim, might or might not be treated as part of the invention depending on a complex of factors, including whether the claim reads as a complete sentence without it, whether the same words are used in both the preamble and the body of the claim, whether the body of the claim includes the magic word 'said,' whether the preamble merely claims a use, benefit, or environment for the claim, and whether the preamble 'is necessary to breathe life and meaning into the claim.'
In Part I I discuss the bizarre body of law around patent claim preambles and how the law got to its current confused state. In Part II I suggest that the rule serves no useful purpose, and that if and when the Supreme Court gets such a case it should and will sweep the rule away. Patent applicants should be drafting patents with that fact in mind, and the rest of us should be interpreting claims with one eye on the fact that this is a doctrine whose days are numbered."
In short, this article asks courts drop the case by case determination test we use today on whether the preamble is a part of the claim just as much as the body of the claim. Saying the preamble always counts as proposed removes uncertainty, but means more patent claims will be held to not infringe. Further, this helps defendants rather than patent owners since a non-infringement defense is preferred to proving invalidity in court.
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