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    “Obviousness or “inventive step” as the Act calls it (see above), is dealt with in section 3 of the Act:

    “An invention shall be taken to involve an inventive step if it is not obvious to a person skilled in the art, having regard to any matter which forms part of the state of the art by virtue only of section 2(2) above…”

    The burden of proof is upon the party seeking to impugn a patent on this ground and this is normally taken up by adducing appropriate expert evidence. In this connection, the party attacking a patent will seek to marshal and prove evidence as to the state of the art in the light of which a particular step is alleged to be obvious. An unusual feature of this case, already noted, is that Hoover have adduced no evidence at all as to the common general knowledge of the art, even though they were in an advantageous position (so one would have thought), to have done so. The only relevant evidence of common general knowledge before me is that of Mr Dyson, being his own experience of contemporaneous events and the inferences which the court can properly draw from it. But that is secondary evidence, which as has been said in a number of authorities, is merely an aid in assessing the primary evidence. I must state at the outset therefore that this lacuna has not assisted the court in assessing the likely status and impact of several prior art citations relied on by Hoover on the mind of the skilled man at the priority date. Hoover were criticised by Dyson in this respect and in my judgment, that criticism is justified. Thus is Hoover’s part of the case.

    As with lack of novelty, the parties were on common ground with regard to the proper approach to obviousness, though each party stressed different aspects of it by reference to relevant authority. I was for example reminded by Dyson of the cautionary remarks of Fletcher Moulton L J in British Westinghouse Electric & Manufacturing Co Ltd -v- Braulik (1910) 27 R.P.C. 209 at 230:

    “… I confess that I view with suspicion arguments to the effect that a new combination, bringing with it new and important consequences in the shape of practical machines, is not an invention, because, when it has once been established, it is easy to show how it might be arrived at by starting from something known, and taking a series of apparently easy steps. This ex post facto analysis of invention is unfair to the inventors and in my opinion is not countenanced by English patent law.”

    I was also reminded of Lord Diplock’s remarks in Technograph (supra, at p.362) where he said:

    “The cross-examination of the respondents’ expert followed with customary skill the familiar “step by step” course. I do not find it persuasive. Once an invention has been made, it is generally possible to postulate a combination of steps by which the inventor might have arrived at the invention…if he had started from something that was already known…”

    Hoover drew my attention to the impropriety of attaching weight to the evidence of what the inventor did since (for example) he may or may not be the apotheosis of the hypothetical skilled man. As Laddie J said in Hoechst Celanese Corp -v- BP Chemicals Ltd [1997] F.S.R 547 at 565:

    “…analysis after the event of the logical steps he took to arrive at the invention is no evidence that it is obvious. If he is an inventive man he will no doubt see things more clearly than his notional non-inventive colleague.”

    Further on the Hoechst Celanese case, Dyson drew my attention to a proposition upon which they strongly rely on the question of obviousness, that is, that for obviousness to be established, there must be a motive for taking allegedly obvious step. Support for this proposition is to be found both from the words of Laddie J on p. 575 and from the judgment of Slade L J Hallen Co v Brabantia (UK) Ltd [1991] R.P.C 195 at 212 which Laddie J quotes:

    “We … accept the plaintiff’s submission that, for the purpose of testing obviousness, one cannot assume that the skilled person simply makes technical trials for the sake of doing so.”

    Laddie J has integrated the above requirement of “motive” into the well-established approach of the European Patent Office to inventive step, namely, that of enquiring as to whether a particular solution to a problem is or is not an obvious one to take. He cites various authorities and concludes this:

    “All of those passages are consistent with the Object/Solution approach to obviousness adopted by the Technical Board of Appeal of the EPO. Even if the step from the prior art is a small one, to prove obviousness it is necessary to demonstrate that there is some reason for taking it.”

    In my judgment, if at the relevant time, the skilled man perceived no problem which required to be solved, the task of the protagonist wishing to establish that the taking of a particular step (or a fortiori, steps) which would bring an item of prior art within the scope of the claim under attack was obvious, becomes considerably more difficult. However, as the next authority makes clear, one must assume that the skilled man will approach the prior art citation with interest; there is no question for instance of spontaneous rejection of matter forming part of the state of the art, as at one stage, Dyson came close to suggesting.

    It was common ground that the issue of obviousness should in general be approached in the fourfold structured manner proposed by Oliver L J in Windsurfing International v Tabur Marine (Great Britain) Ltd [1985] R.P.C 59 at 73:

    “… The first [step] is to identify the inventive concept embodied in the patent in suit. Thereafter, the court has to assume the mantle of the normally skilled but unimaginative addressee in the art of the priority date and to impute to him what was, at that time, common general knowledge of the art in question. The third step is to identify what, if any, differences exist between the matter cited as being “known or used” and the alleged invention. Finally, the court has to ask itself whether, viewed without any knowledge of the alleged invention, those differences constitute steps which would have been obvious to the skilled man or whether they require any degree of invention.”

    A little earlier the judge observed (p. 72):

    “What has to be determined is whether what is now claimed as inventive would have been obvious, not whether it would have appeared commercially worthwhile to exploit it.”

    Dyson Appliances Ltd -v- Hoover Ltd [2001] Reports of Patent, Design and Trade Mark Cases