INTELLECTUAL PROPERTY SOCIETY OF AUSTRALIA AND NEW ZEALAND
26TH ANNUAL CONFERENCE – 7- 9 SEPTEMBER 2012
“The Skilled Addressee”
The Honourable Justice John Middleton
9 September 2012

INTRODUCTION
The grant of letters patent, conferring a monopoly and thereby effectively interfering with freedom of trade for a fixed period, was historically an exercise of the Crown’s prerogative.  Such prerogative was required to be exercised only “for the advantage and good of the people, otherwise they ought not to be allowed by law”.  Thomas Terrell said the following about the rationale underpinning the grant of letters patent:
By the creation of monopolies to first and true inventors in the right of using their inventions, a species of property is created in favour of inventors, as a reward for the benefits which they have conferred on humanity, by the exercise of their thought, knowledge and industry. It is to the interests of the community that persons should be induced to devote their time, energies and resources in furtherance of the development of arts and manufactures, and this was recognized in England from the earliest periods which can pretend to be described as civilized.
It was to the advantage of the whole community that inventors should be rewarded, and no measure of reward can be conceived more just and equitable, and bearing a closer relation to the benefit conferred by the particular inventor than to grant him the sole right of making using and vending his invention for a limited period of time.
Prior to 1624, monopolies fell into two categories: first, those that were granted in return for the introduction or invention of a new trade or article, and secondly, those granted in restraint of trade in articles and arts already known.  This latter category of monopoly was typically granted to courtiers or those attached to the Crown service.  T M Stevens, the author of the second edition of Edmunds on Patents, had the following to say about the two classes of monopolies:
The [first] class (provided that the monopoly was granted only for a limited time) was defensible as an encouragement and reward for ingenuity, work, or expense incurred producing an addition to the material wealth of the nation.  The [second class] was unalloyed evil, contrary to the common law, and not worthy of being made an exception to the rule that a grant in restraint of trade is invalid.
This second and objectionable class of monopoly was eventually prohibited by the 1624 Statute of Monopolies, which served to codify much of the common law regarding patents.  However, even today there remains a tension in patent law policy – namely, the need to balance the interests of the public in receiving the benefit of new inventions with the interest of free trade.  It is desirable to support patents for meritorious discoveries, but also to protect the public against monopolies where the alleged ‘inventions’ are not of any real merit.  It is for these reasons that the question of patent validity is governed by such tests as novelty, inventive step and utility – these are the checks and balances that ensure the striking of “a balance of policy considerations in patent law[,] of encouraging and rewarding inventors without impeding advances and improvements by skilled, non-inventive persons”.  
Central to many of these patent law tests is a “wraith-like legal creature” that is said to “[stalk] the Reports of Patent Cases just as the ‘reasonable man’ does the treatises on tort”, and which is the subject of my speech to you today – the ‘skilled addressee’.  
Generally speaking, the skilled addressee is the person who works in the relevant field of art or science with which the invention in a given case is connected.  They are of ordinary skill, and are equipped with common general knowledge in the art.  They do not necessarily need to be formally qualified – instead, they may have practical skill in the field.  They are a construct, a hypothetical person – or in some cases, team of people – through whose eyes the Court is required to assess the patent for various purposes.
the skilled addressee may be described as ‘wraith-like’ not least of all because of the variety of names attributed to them over time, in different contexts.  As recognised by Justice Finkelstein in Root Quality v Root Control, sometimes they are the “notional skilled addressee”.  At other times, they are the “uninventive skilled worker in the particular field”.  Sometimes they are the “non-inventive worker in the field”.  At other times – as in the Patents Act 1990 (Cth) (the Act) – they are the “person skilled in the art”.  They have also been referred to as the “non-inventive hypothetical skilled addressee”.  This is by no means an exhaustive list.  I understand all of these expressions to be referring to the same person, to whom I shall refer (for the purpose of consistency in this paper) as ‘the skilled addressee’.
CONTEXTS IN WHICH THE SKILLED ADDRESSEE IS INVOKED
The skilled addressee is called upon in a number of contexts in both the Act and Australian patent law more generally:  
1.	Construction
The first of these contexts is construction.  Although the construction of a specification is a question of law and ultimately a matter for the Court, it is the skilled addressee to whom a patent is addressed and through whose eyes the patent must be construed.  
In some instances, a Court will need the assistance of expert evidence in order to undertake this task: to explain “what is the generally accepted meaning of technical terms and also to explain how things actually work”.  Such evidence will be essential where a patent uses technical terms.  Patent claims and specifications are to be construed in light of the skilled addressee’s common general knowledge and the body of the specification.
2.	Novelty
The next context is novelty, which is a key criterion of patent validity.  It is the knowledge of the ‘person skilled in the relevant art’ that will determine whether a patent is novel.  Novelty is dealt with in sections 7 and 18 of the Act.  The question is whether the person skilled in the relevant art, having reference to the prior art and common general knowledge at the relevant time, would have perceived the invention without exercising inventive ingenuity. 
3.	Inventive step
The person skilled in the relevant art will also judge whether a patent contains an inventive step.  Inventive step is dealt with in sections 7 and 18 of the Act.  Here, the inquiry is whether the invention was obvious; namely, whether the person skilled in the relevant art (having reference to the relevant prior art and common general knowledge at the time) would have been led as a matter of course to try the invention in the expectation that it would have produced a useful result.  If this is made out, the patent will of course be invalid for want of inventive step.
4.	Usefulness
The person skilled in the relevant art also plays a role in determining the usefulness of a patent, which is stipulated as a requirement for validity under section 18 of the Act.  This inquiry requires the Court to construe the patent as the person skilled in the relevant art, who is desirous of making the invention.
5.	Sufficiency
Finally, section 138(3)(f) of the Act provides that a patent may be revoked on the ground that the specification does not comply with ss 40(2) or (3) of the Act.  Section 40(2)(a) of the Act requires a complete specification to “describe the invention fully, including the best method known to the applicant of performing the invention”.  In Kimberly-Clark Australia Pty Ltd v Arico Trading International Pty Ltd, the High Court explained that under this section, the question is:  
will the disclosure [in the specification] enable the addressee of the specification to produce something within each claim without new inventions or additions or prolonged study of matters presenting initial difficulty?
For these purposes, the addressee of the specification is the skilled addressee.
Further, I note that from 15 April 2013, the Act will contain even more references to the ‘person skilled in the relevant art’:  
a)	Section 7A will be inserted into the Act to expressly define when an invention is ‘useful’ – specifically, sub-section (2) of this section will provide that “the disclosure in the complete specification must be sufficient for that specific, substantial and credible use to be appreciated by a person skilled in the relevant art” (emphasis added).  
b)	Express references to a ‘person skilled in the relevant art” will also be inserted into sections 40, 43, 114 and 114A (sections which address specifications and priority dates) to make it clear that specifications must disclose the invention in a manner which is clear and complete enough for the invention to be performed by a person skilled in the relevant art. 
At the outset, I should say that issues of construction can in some cases be determined without the assistance of skilled addressee evidence, or without non-inventive skilled addressee evidence.  In Britax Childcare Pty Ltd v Infra-Secure Pty Ltd, I concluded that there is no absolute need for a person to have a non-inventive quality before they can be qualified to give evidence on construction of a patent.  
In Australian Mud Company Pty Ltd (ACN 009 283 416) & Ors v Coretell Pty Ltd (ACN 119 188 493) & Anor Barker J accepted that an inventive person could assist on construction, even if they are not the non-inventive skilled addressee of the patent in suit.  In the context of determining the suitability of an expert witness proposed by the applicants in that case as the ‘skilled addressee’, His Honour said:
The respondents concede that the field of the invention, core sample orientation tools, could include, or overlap with, the discipline of mechatronic engineering. To this extent the respondents accept that Professor Trevelyan is a competent witness. However, the respondents say that Professor Trevelyan is inventive and therefore cannot be regarded as a non-inventive skilled addressee. The respondents supported this contention by tendering a schedule outlining the patenting activities of Professor Trevelyan... Consequently, the respondents say that the court should qualify the weight to be attributed to Professor Trevelyan’s evidence…
The applicants say that although Professor Trevelyan might himself be described as inventive this should not disqualify him from addressing the court in relation to the patent. Professor Trevelyan’s uncontested evidence is that as a professor of mechatronics he is required to work closely with and supervise his own students — many of whom work in the mining industry — and this gives him considerable insight into how a person skilled in the art would understand the patent: transcript, pp 147, 197. The applicants say that this information is relevant and assists the court in construing the claims in the patent.
I accept that Professor Trevelyan’s evidence is relevant to the issues in dispute in this proceeding and I accept that his evidence may go to what the non-inventive but skilled worker engaged in the design, manufacture or operation of core sample orientation tools would understand the patent to mean. However, given the uncontested evidence that Professor Trevelyan is inventive, I do not accept that he himself is the non-inventive skilled addressee of the subject patent. 
The decision of Barker J was appealed and his decision was affirmed, although His Honour’s comments on the skilled addressee were not the subject of the appeal decision.  
WHAT IS THE SKILLED ADDRESSEE?
Generally speaking, the first step for identifying the appropriate skilled addressee is to identify the field of knowledge to which the invention relates.  This is important because the identification of the relevant field of knowledge will, in turn, determine the characteristics of the skilled addressee.  Care must be taken before a judge in making this identification, because it may lead to unhappy consequences in the presenting of evidence before a court.
In the case of Fina Research SA v Halliburton Energy Services Inc, the Federal Court at an early stage of a trial ruled inadmissible expert evidence of a purported “skilled addressee”.  The Court did so because the description of the required “skilled addressee” did not correspond to that of the experience and expertise of the expert witness to be called.
In this case, the Court decided that the appropriate characterisation of the attributes of the skilled addressee was a person with a requisite specialised knowledge in formulating drilling mud.  The question that arose was whether the proposed expert was such a person.  The patent concerned the composition of drilling mud.

Senior Counsel for the applicants submitted that the skilled addressee was an industrial chemist in a drilling mud laboratory or mud company laboratory formulating muds.  

The proposed expert witness had general expertise as a chemist with considerable knowledge of, and experience with, the petroleum industry.  However, he did not have experience in formulating drilling mud.  Without such experience he was not in a position to give relevant evidence of assistance to the court concerning the formulation of drilling mud bearing on the meaning of a patent application, the issue of novelty or the issue of obviousness.
I now turn to the nature of the skilled addressee.
Justice Kirby made the following comments about the role and characteristics of the evidence relating to the skilled addressee in his dissenting judgment in Alphapharm:
It is appropriate to remember why courts in the past have invented the hypothetical formulator instead of simply expressing their own opinions on subjects of this kind. The reason for interposing this fictitious person is clear. Judges themselves (or juries in the days when juries decided such questions) could not be expert in all the fields of science and technology involved. They were, therefore, invariably reliant upon expert evidence in the particular field to prove what was “obvious” at the relevant date and what was not; what involved in “inventive step” and what did not. It would defeat the purpose of the Act if the applicable test were to be expressed in terms of what was obvious, as such, to a jury, to a judge or even to a reasonable person. It follows that the posited formulator must necessarily have some knowledge of the relevant art, if only to be in a position to evaluate the presence, or absence, of obviousness. What is imagined cannot be a layman completed unskilled in the art. It must be someone sufficiently skilled and competent to answer the questions posed by the Act. A dullard or ignoramus the hypothetical formulator cannot be. And yet courts have also said that what is required is someone skilled but “non-inventive” or someone “unimaginative” or someone “lacking in inventive capacity”.
In Catnic, Lord Diplock said that skilled addressees are “likely to have a practical interest in the subject matter of [the] invention”.  Depending on the invention in question, this person may, therefore, need to be skilled in more than one art.  In such a situation, the Court may conceive of not just one skilled addressee, but a whole team, whose combined skills are to be employed the patent law tests I previously set out.  This is often the case in highly technical fields such as pharmaceutical patents.  In such a case, evidence will usually need to be led about how the team members would interact to solve problems.
The extent of a skilled addressee’s knowledge and experience may well impact differently on the result in any given case depending on context.
One example of this is the inquiry undertaken by the Court regarding the common general knowledge that is to be attributed to the skilled addressee for different purposes under the Act.  In the inventive step inquiry, the more extensive the knowledge base of a skilled addressee, the greater the likelihood of a patent claim being found to be obvious.  In contrast, when considering insufficiency, if a skilled addressee has a very expansive knowledge base, this can increase the chances of the patent being found to provide a sufficient description of the invention and the method by which it is to be performed.
The common general knowledge of a skilled addressee in a particular case will be determined in large part by the level of skill that is attributed to them by the Court.  This, too, is a balancing exercise.  If the skill level is set too high, there is the risk that every supposedly inventive step will seem obvious.  Conversely, setting the level of skill too low may produce the opposite result, and fail to screen out those inventions that are in fact obvious.  
It is to be expected that the level of skill imputed to a skilled addressee – who is typically described as being “of ordinary skill in the art” – will vary according to the specific facts of each case.  It is said that where a field is occupied by practical tradesmen rather than by scientists, claims should be considered against the background of that field – not of: 
some unreal field peopled by a technological elite. What must be taken into account is the common general knowledge and skill of the relevant calling.
However, in some fields, different considerations apply.  For example, with pharmaceutical or veterinary patents, courts have recognised that the skilled addressee (or team) may have PhD qualifications in a relevant field of science.  In such fields, the skilled addressee may also have a capacity for original research.  
Other characteristics of the skilled addressee (or their team) include the fact that they have the best equipment available to them, and are not constrained by either the amount of time they can address to a particular problem or how they obtain their funding.  The Full Court in Fallshaw Holdings cautioned that in considering the attributes of the skilled addressee, a court should “not ignore the rapid advance of technology during the present century, which has certainly enhanced the equipment that skilled persons in many arts bring to the solution of their problems”.
They may also be “well versed in the periodical literature of their subjects”, and carry out library or electronic searches.  In some fields, the skilled addressee may even make themselves familiar with patent specifications as they become available for inspection.  At least in the context of pharmaceutical development, for example, the notion that the relevant skilled addressee “sits alone, speculating with nothing more than knowledge remembered from university lectures that are retained at the front of the mind”, has been rejected.
The skilled addressee – or their team – may also have certain specialist facilities available to them.  For example, if evidence shows that a team of skilled addressees at a certain date would have sub-contracted certain tasks to outside workers, this may be built into the ‘skilled addressee’ concept in a particular case.  The skilled addressee may also attend and deliver papers at conferences (either domestically or internationally).
Finally, it is often said that one of the key characteristics of the skilled addressee is non-inventiveness, or what is sometimes referred to as a complete lack of imagination or ingenuity.
It is said that the description of the skilled addressee in this way, as the non-inventive and unimaginative worker in the field, is designed to exclude patentees and others of particularly inventive disposition.  This is supposedly designed to ensure that the various tests for patent validity that invoke the skilled addressee – novelty, inventive step, etc – are all applied objectively by the Court, and that, where expert evidence is led to assist the Court in constructing the skilled addressee in a particular case, the risk that such evidence is tainted by that witness applying hindsight or a particular bias is minimised.  
However, a complicating factor in this analysis is that in highly technical fields (such as biotechnology or pharmaceuticals), a degree of inventiveness, ingenuity or initiative is effectively a pre-requisite for being involved in that field in the first place.  In such circumstances, the concept of the utterly non-inventive skilled addressee is potentially very artificial indeed.  
This brings us to the question: must the skilled addressee always, in all contexts in which they are invoked under Australian patent law, be non-inventive?
MUST THE SKILLED ADDRESSEE ALWAYS BE NON-INVENTIVE?
In the recent matter of Britax, I was required to consider the role of the skilled addressee in the context of patent construction.  Two principal issues arose for consideration:
(1)	whether the characteristics of the skilled addressee (and in particular, their defining characteristic of non-inventiveness) must always be the same, regardless of the context in which this hypothetical construct is invoked; and 
(2)	whether persons giving expert evidence to assist the Court in the construction of the skilled addressee in a particular case must similarly always be non-inventive.
The Britax decision only related to construction, and other aspects of the case are still being litigated.
I concluded that the attributes of the skilled addressee do not necessarily need to be the same in the context of claim construction on the one hand, and novelty and inventive step on the other.  As a matter of statutory construction, it may be that the term “person skilled in the relevant art” as referred to in the Act is to be construed so that their characteristics are the same for the purpose of both ss 7(1) (novelty) and 7(2) (inventive step) in any given proceeding.  However, the principles of patent construction and the role of the skilled addressee in this context are not controlled either by that statutory term, or any perceived need for consistency in the use of the term “person skilled in the relevant art” when interpreting the Act.  
The Act does not expressly refer to the principles applicable to interpreting a patent, so I did not consider myself to be bound (as a matter of statutory construction) to require that the skilled addressee involved in assisting with the construction of a patent have the same attributes as the ‘person skilled in the relevant art’ referred to in ss 7(1) and 7(2).  
The idea that the characteristics of the skilled addressee - in particular, their level of inventiveness - may differ according to the context in which they are invoked finds support in a number of decisions made by Courts in both Australia and other countries.  Genentech was one such case and is instructive.  In this case – decided by the UK Court of Appeal in 1988 – Genentech sued The Wellcome Foundation, alleging infringement of a patent concerned with the synthesis and manufacture of human tissue plasminogen activator protein using recombinant DNA technology.  The Wellcome Foundation counter-sued for invalidity of Genentech’s patent.  
When considering the team of people who were ‘skilled in the art’ and required for the purpose of determining questions of insufficiency and inventive step in that case, Lord Justice Mustill concluded that “in a case like this no such person exists”.  Further, in the course of considering the attributes of this team of skilled addressees, His Lordship noted that “traditional patent law, and indeed the current legislation, is ill at ease with this type of complex and rapidly developing new technology”.  
His Lordship acknowledged that “the authorities show… that the hypothetical team is to be credited with no inventive capacity at all”, but felt that a distinction needed to be drawn between the skilled addressees invoked in the different contexts of inventive step and insufficiency under UK law in the field of recombinant DNA technology.  Lord Justice Mustill said:
Each of these [sections of the relevant UK patent legislation] refers to the person skilled in the art, and it has been assumed that since the words are the same the person and his attributes must also be the same, whichever section is in play. In the case of the classical mechanical engineering patent, this is true. Whether one is asking if the addressee can read the drawings and the description, so as to be able to work the invention, or if the skilled man can proceed from the drawings and descriptions of the prior art to the new product or process without inventiveness, there is no difficulty in using the same notional skilled artificer as the touchstone. But the position here is different. Once given that we are concerned with a series of different arts practised in this complex field, it cannot be assumed that the arts in which the hypothetical persons are skilled will be the same whether they are addressees who start with the patent and try to make it work, or persons who start with the prior art and try to get to the patent. This is indeed obvious in the present case, since the amino-acid sequencer who is a vital member of the discovering team will be redundant when the addressees are seeking to fabricate (say) the claimed expression vectors, since ex hypothesi they will know, not just the five or six bases which were derived en route to the discovery but the full length of the protein sequences.
(emphasis added)
His Lordship continued: 
Equally, I am not persuaded that the standard of attainment contemplated by the sections will always be the same (although it will often be the same) for the individual members of the notional addressee team as for the notional discovery team. To work the patent, the addressees follow the instructions, filling in gaps and clarifying obscurities by common sense and trial and error. This may require skill and experience, but not inventive facility. But the discovery team has no instruction to follow. Unlike the addressees it does not know the answers in advance, and in practice the people who constitute it will be required to exercise different talents from those who take the information disclosed in the patent and put it into practice. 
In my judgment this distinction lies close to the heart of what has seemed to me one of the most confusing aspects of this difficult case, namely the undoubted presence in the authorities of statements which seem to deny to the skilled man any inventive capacity at all. This surely cannot be applied in a literal way to cases like the present, for if it were so an invention could scarcely ever be obvious, since all the routes to the desired end are likely to throw up problems, more or less knotty. This problem does not arise in the context of s 14(3) [a section concerning insufficiency]. If one is asking whether the patent teaches the reader how to work the invention, the fact that it cannot be worked unless the addressee himself makes an invention must be fatal, since it demonstrates that the description is insufficient. But where one is looking at the research team, one cannot treat them as dull plodders, for such people would not be members of the team at all, except as laboratory assistants. We have to envisage people who are skilled, and skilled in the art. Here we have a difficult art, in which the skill consists in a substantial degree of an ability to solve problems. It must, I consider, follow from this that the hypothetical skilled man must be credited with that particular ability in the appropriate degree. 
(emphasis in bold added)
His Lordship concluded:
Where the art by its nature involves intellectual gifts and ingenuity of approach, it would, I believe, be wrong to assume that the hypothetical worker is devoid of these gifts. 
These observations were made in the context of a team of skilled addressees, operating in a highly technical field.  Of course, it is important to note that Justice Bennett in H Lundbeck A/S v Alphapharm Pty Ltd cautioned that “[c]are must be taken in applying United Kingdom jurisprudence on the 1977 Act (UK) to Australian patents”.  Further, the High Court in Alphapharm warned that the treatment of ‘obviousness’ by the UK Court of Appeal in Genentech represents the divergence of European law from the Australian treatment of obviousness.  
However, in my opinion, his Lordship’s observations - about the tensions created by the historical assumption that the skilled addressee is utterly uninventive in all contexts - merit further consideration.  As far as I am aware, no Australian Court has yet expressly grappled with (or expressly rejected, for that matter) Lord Justice Mustill’s comments in Genentech. 
Further, the prospect that the skilled addressee need not always be non-inventive was independently raised by Justice McHugh in his dissenting judgment in Alphapharm.  In that case, his Honour asserted that “[a] judge trying the obviousness issue is not bound, as a matter of law, to determine that issue by reference to persons who are not “particularly imaginative or inventive””.  His Honour continued:
These statements, and similar ones, have been made by judges, highly experienced and eminent in patent law, and applied by many other judges. A judge faced with a situation similar to those dealt with in a judgment containing one of these statements would be well advised to follow it, reflecting as it does the collective wisdom of the judiciary on this type of situation. And to do so helps to achieve consistency in fact finding, a matter of great importance if the law is to maintain the confidence of litigants. Equal justice under the law requires that like cases should be decided alike. Nevertheless, all such judicial statements merely reflect reasoning processes concerning factual issues. They do not lay down any legal principles and they have no precedent value. They are not binding upon judges hearing future cases.
In many fields of law governed by statute, such as income taxation, workers' compensation, environmental planning and patents, judges and practitioners, who specialise in those fields, have a tendency to treat judicial statements, determinative of particular cases, as principles of law. Few of them are. Most of the time, they simply reflect how experienced judges have resolved particular factual situations. As Dixon CJ once said (132), in rejecting an argument that a departure from observations made in an earlier case warranted the grant of special leave to appeal, ``it is not everything that appears in the Law Reports that is law''. Some may see this statement as a cynical reference to the Law Reports containing erroneous statements of legal principle. But given its context, I think that the great Chief Justice was emphasising that many statements in the Law Reports are concerned with reasoning about factual situations.
HISTORY OF THE SKILLED ADDRESSEE
For the purpose of preparing this paper, my Associate tried to trace the concept of the skilled addressee back through the case law to its origins.  It proved to be wraith-like indeed.  This inquiry was complicated by the issue identified by Justice Finkelstein in Root Quality v Root Control – the skilled addressee goes by many names, which has implications for conducting electronic searches of case law databases.  Further, the archives of UK patent law in Australia are finite – there came a point when we had tracked the concept back to case law from 1778, but could go no further.  
It is important to note that the context in which the question has arisen in the old cases is usually in the context of sufficiency of the patent.  As I have alluded to, context may be important in determining the exact characteristics and role of the skilled addressee.
So with those caveats in mind, the earliest reference we were able to find to the skilled addressee in the UK case law available to us was an obscure reference to this concept appearing in the 1778 case of Liardet v Johnson.  In this case, Lord Mansfield stated that one of the “general questions on patents” was “whether the specification is sufficient to enable others to make it up”, as “[t]he meaning of the specification is, that others may be taught to do the thing for which the patent is granted”.  Regrettably, his Lordship did not see fit to elaborate on who these ‘others’ might be.
The next case we were able to find was that of Arkwright v Nightingale, a case in which, in the context of argument about the sufficiency of the patent in question, it was asserted by Counsel for the plaintiff (Mr Arkwright) that:
If an ingenious mechanic were to make a new invention in clocks or watches, it would not be incumbent upon him to make a specification intelligible to a common cobbler.  The person who is to make from the specification must be acquainted with the construction of watches in use before; and it will be sufficient in the principle of common sense, and to satisfy the requisition of the law, if the specification is sufficient to enable a skilful watchmaker, who knew nothing of the invention but from the specification, to add the improvements to the movements that were before in use. 
Lord Loughborough agreed, stating that:
The clearness of the specification must be according to the subject-matter of it; it is addressed to persons in the profession having skill in the subject, not to men of ignorance, and if it is understood by those whose business leads them to be conversant in such subjects, it is intelligible. 
Despite his Lordship finding in favour of Mr Arkwright (and his patent for machines that spun material such as silk and flax), later that year came the case of R v Arkwright, in which Mr Arkwright was required to defend a writ of scire facias to repeal his patent, purportedly based on grounds including (a) that the grant was “prejudicial and inconvenient to the King’s subjects in general”, and (b) that Mr Arkwright had not sufficiently described his invention in the patent specification.  This time, Justice Buller was required to consider considered the sufficiency of the patent, and stated:
It has been truly said by the counsel, that if the specification be such that mechanical men of common understanding can comprehend it, to make a machine by it, it is sufficient; but then it must be such that the mechanics may be able to make the machine by following the directions of the specification, without any new inventions or additions of their own. 
In the 1787 case of Turner v Winter, the Court of King’s Bench made the following comment about the sufficiency of patents:
It is sufficient if persons of skill can understand the process by means of the specification, so as to keep alive the discovery after the patentee's exclusive title is expired.
In the 1809 case of Harmar v Playne, the same Court stated:
It may not be necessary, indeed, in stating a specification of a patent for an improvement, to state precisely all the former known parts of the machine, and then to apply to those the improvement; but on many occasions it maybe sufficient to refer generally to them… The meaning of the specification was that others might be taught to do the thing for which the patent was granted, it must be understood to enable persons of reasonably competent skill in such matters to make it; for no sort of specification would probably enable a ploughman, utterly ignorant of the whole art, to make a watch.
…
It is not enough then that persons of great skill and experience may be able to find out the invention from the specification; but it should be plainly stated, so that a person of reasonable knowledge and experience upon the subject may immediately be made acquainted with the invention.
In the 1825 case of Bloxam v Elsee, the Assizes Court considered the sufficiency of a patent, and commented that:
An inventor of a machine is not tied down to make such a specification, as, by words only, would enable a skilful mechanic to make the machine, but he is to be allowed to call in aid the drawings which he annexes to the specification; and if, by a comparison of the words and the drawings, the one will explain the other sufficiently to enable a skilful mechanic to perform the work, such a specification is sufficient.
However, these cases do not explore in any detail whether the skilled addressee must be non-inventive.  That comes later.  In the 1836 case of Morgan v Seaward, the Court considered the requirement that a specification sufficiently describe the invention.  Approving the comments of Buller J in R v Arkwright, Baron Alderson said:
Mr Justice Buller, in the case of the King v Arkwright, lays down as the criterion, that a man to entitle himself to the benefit of a patent of monopoly must disclose his secret and specify his invention in such a way that others of the same trade, who are artists, may be taught to do the thing for which the patent is granted, by following the directions of the specification, without any new invention or addition of their own.  That is reasonable and proper, for people in trade ought to be told the manner in which the thing may be done in respect of which the patent is granted. –How? Not by themselves becoming investors of a method of carrying it into effect, but by following the specification, without making a new invention, or making any addition to the specification. If the invention can only be carried into effect by persons setting themselves a problem to solve, then they who solve the problem become the inventors of the method of solving it, and he who leaves persons to carry out his invention by means of that application of their understanding, does not teach them in his specification that which in order to entitle him to maintain his patent he should teach them, the way of doing the thing, but sets them a problem, which being suggested to persons of skill, they may be able to solve. That is not the way in which a specification ought to be framed. It ought to be framed so as not to call on a person to have recourse to more than those ordinary means of knowledge (not invention) which a workman of competent skill in his art and trade may be presumed to have. You may call upon him to exercise all the actual existing knowledge common to the trade, but you cannot call upon him to exercise any thing more. You have no right to call upon him to tax his ingenuity or invention. Those are the criteria by which you ought to be governed, and you ought to decide this question according to those criteria. 
(emphasis added)
In addressing the jury in that case, his Honour concluded:
[I]f you shall think that this invention has been so specified that any competent engineer, having the ordinary knowledge which competent engineers possess, could carry it into effect by the application of his skill, and the use of his previous knowledge, without any inventions on his part, and that he could do it in the manner described by the specification, and from the information disclosed in the specification, then the specification would be sufficient. If, on the other hand, you think that engineers of ordinary and competent skill would have to set themselves a problem to solve, and would have to solve that problem before they could do it, then the specification would be bad.
In the 1841 case of Neilson v Harford, during argument on the appropriate test for determining sufficiency of a patent,  Counsel for the defendants submitted:
It is a fundamental rule, on which all others for making and judging of a specification depend, that the secret must be disclosed in such a manner, that men of common understanding, with a moderate knowledge of the art, may be enabled to make the subject of the patent. Nothing to invention, [sic] nothing to experiment… if a person of moderate capacity, having a little knowledge of the science which led to the invention, can immediately see the method pointed out, and easily apprehend the purport for which the subject was invented, without study, without any invention of his own, and without experiments, the disclosure is fully and fairly made.
(emphasis added)
When addressing the jury in that case, Baron Parkes said:
It is to be a person only of ordinary skill and ordinary knowledge. You are not to ask yourselves the question, whether persons of great skill – a first-rate engineer, or a second class engineer, as described by Mr. Farey – whether they would do it; because generally those persons are men of great science and philosophical knowledge, and they would upon a mere hint in the specification probably invent a machine which should answer the purpose extremely well; but that is not the description of persons to whom this specification may be supposed to be addressed – it is supposed to be addressed to a practical workman, who brings the ordinary degree of knowledge and the ordinary degree of capacity to the subject; and if such a person would construct an apparatus that would answer some beneficial purpose, whatever its shape was, according to the terms of this specification, then I think that this specification is good, and the patent may be supported so far as relates to that. 
In 1862, the case of Hill v Evans was decided by the Court of Appeal in Chancery.  Lord Westbury made the following remarks in the context of considering novelty and anticipation:
The question then is, what must be the nature of the antecedent statement? I apprehend that the principle is correctly thus expressed :—the antecedent statement must be such that a person of ordinary knowledge of the subject would at once perceive, understand, and be able practically to apply the discovery without the necessity of making further experiments and gaining further information before the invention can be made useful.
(emphasis added)
In the 1876 case of Plimpton v Malcolmson, Master of the Rolls Jessel made the following comments about sufficiency of patents:
Now, what is the meaning of it being a sufficient specification? Upon that there has been a very great deal of authority. Judges have stated it in different ways, no doubt, but I do not think there is much difference in substance. 
In the first place, it is plain that the specification of a patent is not addressed to people who are ignorant of the subject-matter. It is addressed to people who know something about it. But then there are various kinds of people who know something about it. If it is a mechanical invention, as this is, yon [sic] have first of all scientific mechanicians of the first class, eminent engineers; then you have scientific mechanicians of the second class, managers of great manufactories, great employers of labour, persons who have studied mechanics—not to the same extent as the first class, the scientific engineers, but still to a great extent—for the purpose of conducting manufactories of complicated and unusual machines, and who therefore must have made the subject a matter of very considerable study; and in this class I should include foremen, being men of superior intelligence, who like their masters would be capable of invention, and like the scientific engineers would be able to find out what was meant even from slight hints, and still more from imperfect descriptions, and would be able to supplement, so as to succeed even from a defective description, and even more than that, would be able to correct an erroneous description. That is what I would say of the two first classes, which I will call the scientific classes. The other class consists of the ordinary workman, using that amount of skill and intelligence which is fairly to be expected from him—not a careless man, but a careful man, though not possessing that great scientific knowledge or power of invention which would enable him by himself, unaided, to supplement a defective description, or correct an erroneous description. Now, as I understand, to be a good specification it must be intelligible to the third class I have mentioned, and that is the result of the law. It will be a bad specification if the first two classes only understand it, and if the third class do not. I do not think when the cases come to be examined, there is really any difference between the Judges on this point. Their language differs, but I do not think the cases differ.
The Master of the Rolls then referred to Baron Alderson’s observation in Morgan v Seaward - that a patentee cannot call upon a workman of competent skill to exercise his ingenuity or invention – and continued:
Of course that is open to the observation that the meaning of the word “invention” may differ to different minds, and it is sometimes impossible to draw the line between perception and invention. We had an instance of that in the present case. One man may see from a drawing that which ninety-nine men out of a hundred cannot see. The witness Mr. Hulse stated he had a peculiar faculty for seeing from a drawing things other people did not see, and he likened it to the man who could read music at sight—could read a piece of music he had never seen before, as compared to the ordinary mortal who enjoys no such privilege. But again, as I said before, some people might have said that what he thinks is perception is invention. In fact, he describes it as intuitive perception, a peculiar power. Many people would call that the power of supplementing, by invention what the drawing disclosed to ordinary persons. It is quite impossible to say, without considering the concrete, that is, without looking at the subject-matter in respect of which you have to decide—it is quite impossible to say, in the abstract, what is invention and what is perception. It is therefore, I think, to be decided by the jury, under the direction of the Judge; or if there is no jury, by the Judge alone, what, having regard to the subject-matter, is an exercise of invention or an exercise of perception. So much for the law. Again, I may say, and this bears on another branch of the subject, that that is important as to another objection, which I should like to dispose of at once, namely, what the specification ought to tell. First of all it ought to tell the workman how to do it; but it need not tell him every detail. Mr. Baron Alderson says this: “Now, a workman of ordinary skill, when called to put two things together, so that they should move, would, of course, by the ordinary knowledge and skill he possesses, make them of sufficient size to move. There he would have to bring, to his assistance his knowledge that the size of the parts is material to the working of the machine. That is within the ordinary knowledge of every workman. He says, ‘I see this will not work because it is too small,’ and then he makes it a little larger, and finds it will work: what is required is that the specification should be such as to enable a workman of ordinary skill to make the machine; with respect to that, therefore, I do not apprehend you will feel much difficulty.” Therefore he does not mean that the man is to shut his eyes, and copy what he sees before him; but he is to do it in an intelligent manner, and when he has made it according to the specification, and sees it will not work, and sees by the ordinary knowledge of his trade what is to be done to make it work, he is to make it work; and if the specification does not mislead, and contains enough to enable the man to do that, then it is sufficient. The other cases upon the subject are numerous. It is sufficient to say that, in my opinion, they do not conflict with what Mr. Baron Alderson lays down in Morgan v. Seaward. 
In the 1885 case of Philpott v Hanbury, Justice Grove stated that for anticipation of a patent to be made out:
There is not the same necessity for accurate description of how an invention shall be carried into effect, for the purpose of anticipating an invention, as there is for the purpose of sustaining a patent in the hands of a patentee, because in the latter case a description ought to be given which ought not to merely inform the minds of every skilled person or scientific person in the trade, but should inform the minds of ordinary people who are accustomed to work at the trade. Therefore I think that there is a distinction; but I am willing to rest my definition or description of what anticipates a patent on this, that there must be a publication which, when read by persons versed in the trade, skilful and well acquainted with the trade (I might even limit it perhaps to those in the trade who are most skilled – the higher class of skilled workmen) would enable them to understand it. If it be such, it anticipates the patent. If it is a mere suggestion, if it is so erroneous in the description that they cannot, by reasonable application of the mind, find out what it means, it does not anticipate the patent. But if it reasonably discloses what the invention is, so that a person skilled in the trade can practice the invention from it, then I am of the opinion that there is anticipation.
…
If these patents were so obscure or so vague that a person could not make them out reasonably by the application of an ordinary mind, or I will not say of an ordinary mind, but of a skilled mind, to them, then I should say that they certainly do not anticipate. But if, with a little trouble, and the reasoning which a dressmaker would apply to any form of patent or design or system for dresses, a person can make them out, which I am convinced has been done in the present case, then I am of opinion that they anticipate the patent. 
Several years later, in 1892, the House of Lords decided the case of The Anglo-American Brush Electric Light Corporation v King, Brown & Co.  In the context of considering sufficiency, Lord Watson said:
it occurs to me that a reader, whether man of science or skilled workman, would probably have been at a loss to discover what Varley meant, and might not have arrived at either shunt or series-shunt winding without some exercise of his inventive faculty.
(emphasis added)
His Lordship continued:
His specification may, notwithstanding that defect, be sufficient to convey to men of science and employers of labour information which will enable them, without any exercise of inventive ingenuity, to understand his invention, and to give a workman the specific directions which he failed to communicate. In that case, I cannot doubt that his invention is published as completely as if his description had been intelligible to a workman of ordinary skill.
(emphasis added)
In 1913 in the case of Gillette Safety Razor Company v Anglo-American Trading Company Ltd, Lord Moulton was required to consider whether there had been anticipation of a patent by prior publication, and invoked the concept of the “ordinarily competent mechanician”.  I consider that his Lordship came very close to explaining the rationale that underpins the requirement that the skilled addressee invariably be non-inventive when he said:
In ascertaining [the effect of the prior publication], the Court must consider what it would convey to the public to whom it was addressed, i.e. mechanicians. I recognise that it would be most unfair to subsequent patentees if we tested this by what it would convey or suggest to a mechanical genius; but, on the other hand, it would be equally unjust to the public to take it as though it were read only by mechanical idiots…
None of these early UK cases cited a common ‘originating source’ for the concept of the skilled addressee, or explained in detail why the skilled addressee must be non-inventive.  However, based on the policy considerations that pervade patent law (and as alluded to by Lord Moulton in the Gillette case), it appears that the concept of the skilled addressee has evolved over time as a means of ensuring that tests of patent validity, such as novelty and inventive step, are applied as objectively as possible.  This is a weapon in the Court’s arsenal to ensure that the appropriate balance is struck between upholding patents and encouraging innovation, and ensuring unmeritorious patents are not granted so that they do not stifle trade.  Review of these early patent law cases show that this consideration has endured over time.  
HINDSIGHT BIAS
One of the problems with a witness who is giving evidence and is in the category of an inventive skilled addressee, is that he or she may bring a certain hindsight bias into their approach in giving evidence.
Hindsight is the phenomenon whereby: 

people who know the answer vastly overestimate its predictability or obviousness, compared to the estimates of subjects who must guess without advance knowledge. Hindsight bias is sometimes called the I-knew-it-all-along effect.
(emphasis in original)

Any hindsight bias that might otherwise affect the application of the skilled addressee’s evidence may well be able to be evaluated in the course of considering the evidence and the ultimate weight to be given to it (as with all witnesses who present evidence to a court of law).  This occurs in other areas of jurisprudence, even where there is a risk of applying inappropriate hindsight.  The mere fact that an expert witness is inventive may not necessarily disqualify them on this basis.  Indeed, in the past, courts have accepted evidence on matters such as sufficiency, construction and infringement from witnesses who are highly qualified and skilled as well as being somewhat inventive.  It seems all to be a matter of degree and the specific factual circumstances of each case.  
Hindsight is a critical issue for judges to bear in mind in the adjudication of any case, but in patent cases in particular.  It is possible that the requirement that has evolved over time that the skilled addressee be non-inventive was the product of two principal concerns on the part of judges – not just the concern that patentees’ work not be judged by fellow inventors (who might be more likely to deem something obvious or not novel by bringing their own skills to bear on a situation, such that the bar for obtaining patents is then set too high – something which may ultimately discourage invention and innovation in society), but also the concern that evidence from such skilled, inventive addressees may be subject to hindsight bias.  As Sheppard J said in Colgate-Palmolive Co v Cussons Pty Ltd:

The important thing to remember and to keep steadily in mind is the danger of applying hindsight. When a court comes to consider whether a claimed invention is obvious, it comes to the question with the benefit (in one sense the disadvantage) of then existing knowledge and practice. It is most difficult to go back, but that is what one must endeavour to do. One therefore needs to take the greatest care to endeavour to see that hindsight plays no part in the decision making process.

Justice Crennan, in an article she wrote on obviousness and inventive step in 2007, also considered the issue of hindsight, and the “inevitable bias in human thinking” that it creates.  Her Honour considered a number of studies that have been conducted since the 1970s on hindsight bias, and concluded that:

The limitation of hindsight is now confidently said to be that individuals routinely overestimate the ex ante predictability of events after they have occurred and, indeed, it has been asserted that individuals are not cognitively able to prevent knowledge through hindsight from impairing their analysis of events. 

Applying this to the patent context, it would follow that even the most honest of individuals will “consistently exaggerate what could have been anticipated in foresight and not only tend to view what has occurred as having been inevitable, but also as having appeared relatively inevitable beforehand.”
This is not a phenomenon limited to patent jurisprudence.  In Rosenberg v Percival, a medical negligence case in which there was an alleged failure to warn a patient about a particular risk that in fact eventuated, Chief Justice Gleeson recognised that:
There is an aspect of such a question which may form an important part of the context in which a trial judge considers the issue of causation. In the way in which litigation proceeds, the conduct of the parties is seen through the prism of hindsight. A foreseeable risk has eventuated, and harm has resulted. The particular risk becomes the focus of attention. But at the time of the allegedly tortious conduct, there may have been no reason to single it out from a number of adverse contingencies, or to attach to it the significance it later assumed. Recent judgments in this court have drawn attention to the danger of a failure, after the event, to take account of the context, before or at the time of the event, in which a contingency was to be evaluated. This danger may be of particular significance where the alleged breach of duty of care is a failure to warn about the possible risks associated with a course of action, where there were, at the time, strong reasons in favour of pursuing the course of action.
Although Rosenberg v Percival was a medical negligence case, the comments made therein are relevant to any factual situation in which hindsight may intrude.  
Other comments have been made about the dangers of hindsight bias in the context of misleading conduct and reliance by investors:  see Agricultural and Rural Finance Pty Ltd v Kirk and Gardiner v Agricultural and Rural Finance Pty Ltd .

CONCLUSION
Where complex and rapidly developing technology is involved (such as is found in the biotechnology and pharmaceutical areas), it may not always be appropriate to invoke an entirely uninventive skilled addressee for the purpose of applying the validity tests.  Equally, the expert witness called to give evidence may need to be inventive, or at least not unimaginative with no inventive capacity.  With the assistance of expert evidence, it should be possible for judges to calibrate the inventiveness of the witness in these cases to a degree that appropriately reflects and achieves the underpinning policy aims in patent law.  
Some may say it would be better to avoid the increased risk of ‘hindsight bias’ by excluding from giving evidence the inventive person.  The mere warning of an expert about hindsight bias may not be enough.  On the other hand, in some contexts the idea of excluding the inventive person seems artificial and difficult of application.  It may in some instances be inappropriate, because of the nature of the patent, to exclude the inventive person from giving suitable evidence to assist the Court.  It may also be that in the particular case of a complex patent the skilled addressee as contemplated in the Act may necessarily need to have a somewhat inventive disposition.
As far as evidence is concerned, the overriding consideration is that the court needs objective and reliable expert help.  To automatically exclude an inventive person may be to deprive the court of such assistance.  The court in any given proceeding has to consider many policy considerations which underpin patent law.  It is always to be remembered that the evidence of the skilled addressee is just a tool to assist the court in reaching the correct balance in considering issues such as inventive step and obviousness by reference to the statutory criteria.  Of course, it is only after the court has determined the characteristics of the skilled addressee for the purpose of the Act, that the court turns to consider what evidence is relevant and of assistance in undertaking the decision making task.