The Formstein Defence Shows Good Form - Lord Justice Birss Comments On The Applicability Of The Formstein Defence In UK Law

Published date11 June 2021
Subject MatterIntellectual Property, Real Estate and Construction, Patent, Construction & Planning
Law FirmMarks & Clerk
AuthorNicholas Fischer, Ian Turner and Mike Gilbert

In this article, we focus on Birss LJ's comments in Facebook v Voxer1 regarding the applicability of the Formstein defence to allegations of infringement under the doctrine of equivalents.

Voxer alleged its patent was infringed by the Facebook Live and Instagram Live functionality under both normal construction and the doctrine of equivalents. In addition to denying infringement, Facebook argued that it was entitled to rely on the Formstein defence.

The patent was found obvious and not infringed (on normal construction and on the basis of equivalents). Despite these findings, Birss LJ went on to consider whether the so-called Formstein defence exists in UK law. The Formstein defence is taken from a German decision of the same name, and has also been considered by the Dutch Court of Appeal and in the US under the principle of "ensnarement".

The defence is effectively an extension of the "Gillette" principle, which provides that a patentee cannot validly claim something which was not new or was obvious at the priority date. The Formstein defence, however, takes the Gillette principle one step further: if a patent is not infringed under a normal interpretation but would be under the doctrine of equivalents, the scope of the patent will nevertheless be limited to a normal interpretation if the consequence of the broad interpretation under the doctrine of equivalents is that the patent would be invalid. Birss LJ acknowledged that the Gillette principle, despite being a well-established aspect of patent law, is rarely relied on outside of the sphere of Arrow declarations because the parties and public usually need to know whether a patent is valid (and not infringed) or invalid.

He then went on to explain the tension between using a broader claim scope under the doctrine of equivalents as a way to invalidate a claim found valid under the normal interpretation:

"So imagine a case in which a claim on its normal construction is valid and not infringed, but a defendant's device is (i) found to infringe by the doctrine of equivalents but also (ii) found to be obvious over the prior art. Is the right answer that the claim is infringed but invalid because its proper scope, taking into account equivalents, encompasses something obvious over the prior art; or is it valid but not infringed on the footing that part of the law of equivalents mandates that if these are the facts the equivalents doctrine does not expand the claim? Either answer can be justified logically....

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