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Claim Differentiation in a Markman Hearing

Posted Friday, March 9, 2012 by Mike Gibbons

A couple of weeks ago, I blogged about the doctrine of claim differentiation. In brief, claim differentiation is seen in patent litigation in the context of claim construction, during which the precise meanings of claim terms is determined. Claim construction takes place in a patent infringement case during a Markman Hearing, which gets its name from the patent law case (Markman v. Westview Instruments, 517 U.S. 370, 388-389 (1996)) in which it was determined by the Supreme Court that claim construction was a task for the judge and not the jury. I had an opportunity to attend a Markman Hearing today, and one of the attorneys invoked the doctrine of claim differentiation in support of his proposed meaning of a claim term.

The plaintiff was arguing that the patent claim allegedly infringed by the defendant (the “claim in suit”) disclosed an item that had a certain size, even though the patent claim did not expressly recite that size. For simplicity’s sake, let’s say the claim recited a box. The plaintiff was asserting that everyone would understand the box could only be 16 units large, and so therefore explicit language in the claim reciting the box being 16 units wasn’t necessary for the claim term to be limited to only a box of 16 units. By contrast, the defendant argued that the claim language should be read to be non-limiting. In other words, the defendant argued that there was no number of units for the size of the box that had been fixed in the patent.

One thing that is unusual about this set of contentions is that in a patent infringement case, normally the plaintiff argues that the claim language should be read very broadly, in an attempt to ensnare as much intellectual property as possible, including whatever the defendant allegedly did to infringe the patent. Conversely, the defendant argues that the claim term at issue should be construed narrowly, so that their activity is outside the meaning of the claim term. The defense attorney in the hearing I attended today in fact noted the strange position he was in as an accused infringer arguing the patent should not be limited.

The defense noted that had the patent drafter meant to limit the size of the box to 16 units, it would have been quite simple to merely add a dependent claim to the claims in the patent that recited a box of 16 units, and so not having done so must mean the patent is intended to be non-limiting as to the size. Here’s where claim differentiation comes in: the plaintiff’s attorney refuted the defense argument that it would have been best to merely add a dependent claim drawn to a 16-unit box if that’s what the patent drafter wanted by invoking claim differentiation. He argued that had a dependent claim for a 16-unit box been present, the doctrine of claim differentiation would have led the court to understand there must have been a reason for the difference between the speculative dependent claim and the claim in suit. And, that the reason in that instance could only be because other sizes would be intended by the claim in suit. So here, the plaintiff argued that claim differentiation would actually tell us that because a dependent claim was not included, that must mean that the claim in suit was limited.

Recall from the earlier blog post that the doctrine of claim differentiation is a sort of backup canon of claim construction. That is, we rely on it when there is no other way to tell from the text of the patent or the prosecution history (the intrinsic evidence) what the term must mean.

In this case, the patent drafter had inserted language that compliance with a particular standard was “preferable,” and that standard called for a 16-unit box. The judge in this case seemed particularly interested in drilling down on what was meant by “preferable.” If effect could be given to this language of the patent, that would take precedence over the doctrine of claim equivalents and lead to a construction for the defense.

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