I had somehow missed this decision last fall and was only alerted to it by the case note in the most recent IPIC bulletin. I am very glad it did not slip by me entirely, because it the case that we needed to generate a rational approach to the use of prosecution history in claim construction.
Residents of nursing homes often need a variety of different medicines to be dispensed on a weekly schedule at different times of the day. The ‘045 patent concerns a system for preparing a pill dispenser which facilitates keeping track of which pills are to be dispensed to which patient at what time of day. It consists of a plastic tray (“container-defining sheet”) with depressions to make a series of containers for holding pills to be taken four times per day (breakfast, lunch, dinner, and bedtime) over seven days . After the pills are placed in the container, it is then covered by a sealing sheet on which is printed information about the prescription such as the names of the patient and the pharmacist, the date, and the medications in each container. All this was known in the prior art. It is important that the sealing sheet be properly aligned with the container, and because nursing home staff prepare many of these dispensers on a weekly basis, it is desirable to have a mechanism for aligning the container and the sealing sheet quickly and reliably. This was the problem facing the inventor . The preferred solution, as described in the specification (p 3 line 13-15) was a positioning means comprising “one and preferably two upwardly projecting protuberances on the top surface of the recessed support,” and a corresponding number of “holes” in the container-sealing sheet (and see similarly p 8-9, describing the preferred embodiments).
Of course, an inventor is not confined to the most advantageous embodiment set out in the specification, and all the independent claims originally claimed a broader positioning means :
Positioning means provided on at least the top surface of the container-defining sheet and on the container-sealing sheet to ensure that, in use, after the container-defining sheet is fitted onto the recessed support, the paper covering is peeled off from the bands of the container-sealing sheet and said container-sealing sheet is positioned on top of the top surface of the container-defining sheet, the bands covered with a self-adhesive material and their tearing lines be in exact superposition on top of the flanges and the dotted lines of the container-defining sheet.
These claims were originally allowed by the Patent Office, but the Notice of Allowance was withdrawn, and the claims were rejected when prior art, the Braverman Patent, was brought to the attention of the Patent Office .
In correspondence with the Patent Office, counsel for the applicant acknowledged that the Braverman Patent anticipated the invention as claimed, but pointed out that :
BRAVERMAN does not disclose or suggest the following structural feature, which is the key feature of the present invention, namely:
d) positioning means provided on at least the top surface of the container defining sheet and on the container sealing sheet.
Such positioning means were defined in former claims 3 and 4 as being preferably protuberances and holes identified by reference numerals 5, 7 and 15 in the drawings of the present application.
Consequently, in order to overcome the objection based on the Braverman Patent, all the independent claims were amended to add a “wherein” clause specifying that the positioning means comprises
at least one upwardly projecting protuberance provided on the top surface of the recessed support, at least one hole provided into the container-defining sheet and at least one other hole provided in the container-sealing sheet, said at least one hole and one other hole being sized and positioned to correspond to and be engaged by said protuberance.
The defendant’s allegedly infringing container device had a raised outer edge of the container, and the sealing sheet was cut to fit, so that the sealing sheet was positioned by slipping it into the container. Prima facie, the defendant’s device did not use “holes” in the sealing sheet, so a key claim construction question was whether the positioning means defined by the wherein clause was an essential element of the claim.
Counsel for the defendants submitted that “it is difficult to imagine a clearer indication of the essentiality of a claim element than its addition to a claim in order to overcome an objection from the Patent Office” . In my view this argument is entirely compelling. How can we allow a patentee to reclaim in litigation ground that was expressly given up in prosecution? This is the fundamental argument for the doctrine of file-wrapper estoppel, and the facts of Distrimedic powerfully illustrate the force of this argument.
Counsel for the patentee responded that prosecution history simply cannot be used in claim construction, relying on this paragraph from Free World 2000 SCC 66:
 In my view, those references to the inventor's intention refer to an objective manifestation of that intent in the patent claims, as interpreted by the person skilled in the art, and do not contemplate extrinsic evidence such as statements or admissions made in the course of patent prosecution. To allow such extrinsic evidence for the purpose of defining the monopoly would undermine the public notice function of the claims, and increase uncertainty as well as fuelling the already overheated engines of patent litigation. The current emphasis on purposive construction, which keeps the focus on the language of the claims, seems also to be inconsistent with opening the pandora's box of file wrapper estoppel. If significant representations are made to the Patent Office touching the scope of the claims, the Patent Office should insist where necessary on an amendment to the claims to reflect the representation.
de Montigny J responded by distinguishing Free World:
 While statements or admissions made in the course of patent prosecution shall not be used for the purpose of interpreting a claim, this is not what the Court is called upon to do in the case at bar. A change in the wording of a claim as a result of an objection from the Patent Office is an objective fact from which an inference may be drawn, and is not the same as representations made to the Patent Office.
There is a valid distinction between a statement or admission and a change in the wording of the claim, but, in my view, it is not enough to distinguish Free World, as statements and admissions were given only as examples of extrinsic evidence, and not an exhaustive definition. The general thrust of Free World is that extrinsic evidence and prosecution history generally are to be excluded.
However, the SCC’s holding in Free World is unpersuasive and unprincipled. The specific arguments made in  are unpersuasive:
 To allow such extrinsic evidence for the purpose of defining the monopoly would undermine the public notice function of the claims,
It would not undermine the notice function, because it operates purely as an estoppel. The worry seems to be that the public might be read the specification and claims, and believe they are safe, only to discover, after the prosecution history is consulted, that they are actually infringing. That would indeed be undesirable, because the public could not tread confidently based on the claims alone, but would have to consult the prosecution history before making any decisions. But this cannot happen. On the usual view, the prosecution history could only be used as an estoppel, preventing the patentee from reclaiming subject matter that it had given up in prosecution. The use of prosecution history can only narrow the claims, not expand them.
and increase uncertainty as well as fuelling the already overheated engines of patent litigation.
It will not increase uncertainty, because the prosecution history estoppel is not a free-standing tool. It will normally operate to clarify the meaning of claims that are uncertain on their face. In principle, the claim might be clear on its face, and then equally clear, but to the opposite effect, when the prosecution history is consulted, but this must be exceedingly rare in practice because it would mean that the examiner accepted a revision to the wording which, on its face, said the opposite of what the examiner had demanded. But in any event, even in that worst case, there would be no increase in uncertainty.
The current emphasis on purposive construction, which keeps the focus on the language of the claims, seems also to be inconsistent with opening the pandora's box of file wrapper estoppel.
It curious that Binnie J considers purposive interpretation to focus on the language of the claims, when Lord Diplock in Catnic  RPC 183, 243 (HL) rejected a “purely literal” approach. The thrust of purposive construction, as compared to what went before, it to place more emphasis on the way a skilled person would read the claims. This necessarily requires going beyond the language of the claims, because a skilled person’s understanding is affected by the context of their experience in the field, their knowledge of the problems faced, and so on. Purposive construction clearly requires more extrinsic evidence, not less, than the lawyerly textual approach which it rejected. I do not see how it is inconsistent with using prosecution history. de Montigny J was quite right to say that “[a] purposive construction should obviously focus on the wording of a claim, obviously, but this is a far cry from saying that nothing else should be considered” 
If significant representations are made to the Patent Office touching the scope of the claims, the Patent Office should insist where necessary on an amendment to the claims to reflect the representation.
The Patent Office did insist on an amendment to reflect the representation, and the very reason we want to consult the prosecution history is to clarify the meaning of that amendment. We might always say that the Patent Office should have insisted on a clearer amendment, but the fact that textual expression is never perfect is the reason why claims construction is a crucial exercise in the first place.
The SCC’s position on the use of prosecution history estoppel is also unprincipled. As the SCC noted in Whirlpool 2000 SCC 67 [49e], a patent “is an enactment within the definition of ‘regulation’ in s. 2(1) of the Interpretation Act.” Purposive interpretation is really nothing more than the modern approach to statutory interpretation applied to the specific context of patents: see my article on “The Essential Elements Doctrine” (2011) 22 IPJ 223, 226-40. Prosecution history is the equivalent of legislative history. At one time there was an exclusionary rule against using any extrinsic aids to statutory interpretation, subject to a few narrow exceptions. That rule corresponds almost exactly to the exclusionary rule set out in Free World  – but that rule has long been abandoned in respect of legislation generally. (See generally Sullivan on the Construction of Statutes, 5th ed, Ch 22.) The SCC now routinely consults legislative history in interpreting statutes. The practice is so common that citations are otiose; a quick database search will reveal multiple recent instances from the SCC alone. It is unprincipled to say that legislative history can be used to interpret legislation, and to acknowledge that patents are legislation as a matter of the Interpretation Act, and yet to refuse to use prosecution history, which is the equivalent of legislative history. Indeed, if anything, the argument in favour of considering prosecution history is even stronger than the argument for considering legislative history, as some of the traditional reasons for excluding legislative history, such as the difficulty of deciding who speaks for the legislature (see Sullivan at 595-98), have much less force in the patent context.
We should return briefly to de Montigny J’s distinction between representations and “[a] change in the wording of a claim as a result of an objection from the Patent Office [which] is an objective fact from which an inference may be drawn.” This is a sound distinction. The closest parallel in general statutory interpretation is legislative evolution, which is to say changes made in the succession of enacted texts. The use of legislative history is well established and is relatively uncontroversial, precisely because, as de Montigny J says, it is an objective fact (see Sullivan 577-78). If there is any kind of prosecution history which should be considered, this is it.
Finally, I note that the prosecution history was only one factor considered by de Montigny J in holding that the positioning means specified by the wherein clause was an essential element, and it was almost certainly not a determinative factor (see eg [211-12]). Consequently, de Montigny J’s holding regarding the use of the prosecution history could easily be distinguished by subsequent courts. It will be very interesting to see whether de Montigny J’s holding is indeed ignored, or if it is confined to changes in claim wording, or if it represents the first crack in the Free World wall, which might eventually lead to a more rational and principled approach to the use of prosecution history.