A High Court judge ruled on Friday that Dan Brown's bestseller The Da Vinci Code did not steal central themes from a 1982 work of non-fiction. The ruling was welcomed by authors and copyright lawyers as a victory for commonsense.

Advert: Free OUT-LAW breakfast seminars, UK-wide: open source software; and data retentionMichael Baigent and Richard Leigh, two of the three authors of The Holy Blood and the Holy Grail claimed "non-textual infringement in a literary work."

Their case was not that a substantial part of the text of their book had been copied; rather, they said that Brown copied "a substantial part of the work to produce an altered copy or a colourable imitation," according to Justice Smith's 51-page ruling. The target of the lawsuit was the publisher of both books, Random House.

Baigent and Leigh acknowledged that copyright should not protect against the borrowing of an idea contained in a work. But they argued that their book made a sequence of connections that no-one had made before. Among them, that the Holy Grail was a metaphor for Mary Magdalene rather than a mere artefact. Mr Brown copied this conjecture, they said, along with other key points 15 in total – that formed the 'Central Theme' lifted by Mr Brown.

Had Baigent and Leigh won, Justice Smith observed, nothing in the case would "stultify creative endeavour, obtain a monopoly on ideas or historical information or create a precedent which extends the boundaries of copyright protection in the sphere of literary works."

He reasoned that the claimants sought to create discussion with their book and intended that discussion to manifest itself in other books. And Justice Smith described their decision to attack only Brown's 43-million-selling DVC – as it became known – as odd.

Justice Smith felt Brown had "genuinely and clearly" acknowledged HBHG. Brown used an anagram of the two authors' names for a villain he called Sir Leigh Teabing. At one point the character removes a copy of HBHG from a shelf and says: "The authors made some dubious leaps of faith in their analysis, but their fundamental premise is sound."

Baigent and Leigh thought Brown had taken too much of the Central Theme – but the ruling suggests they failed to articulate the meaning of the Central Theme. "The point is that if the Claimants do not know with certainty what their Central Theme is how can anybody else possibly know?," wrote Justice Smith.

Justice Smith accepted that "the facts and the themes and the ideas cannot be protected but how those facts, themes and ideas are put together … can be." He added later, "It must be shown that the architecture or structure is substantially copied."

But the only structure identified by the Claimants were the 15 points of the Central Theme. "A single textual theme has no structure; it is just a piece of text which is the way the Claimants ultimately suggested the Central Themes should be considered."

He continued: "The Claimants themselves in this case chose to dissect their Central Themes ultimately into 15 component parts. Having done that in effect they invited the Defendants to attack those component parts on an individual basis. This is not dissection as such in my view; it is a matter of responding to how the Claimants chose to present their case."

Justice Smith described as "incredible" the fact that the Claimants had difficulty formulating their own Central Theme – when they had also claimed that it was always in their minds when they wrote their book.

On the witness stand, Brown denied that he had a copy of HBHG at the time of preparing a synopsis for DVC. Justice Smith did not believe him. "What is extraordinary about Mr Brown's evidence is that he appears to have acquired all of the books that cover this area apart from the one that is described as essential reading," wrote Justice Smith. On another point he observed that Brown "looked like he was making the answer up."

He criticised the defence for not calling Brown's wife to the stand who did the research for the books. "All of this could have been clarified had Blythe Brown given evidence," he wrote. He suspected that Blythe Brown had used HBHG extensively much earlier than Dan Brown admitted.

The judge was even less impressed by Baigent. His own counsel described him as a poor witness in closing submissions; but Justice Smith said "those words do not in my view do justice to the inadequacy of Mr Baigent's performance." His "wild" evidence was "comprehensively destroyed" in cross examination, he noted.

Justice Smith reasoned that, since the Claimants argued that without the Central Theme there is very little in HBHG, it follows that if overall the Central Theme cannot amount to any literary work because it is too general or too low a level of abstraction or because it is a collection of facts and ideas without any architecture or structure then the same must be said of HBHG which is allegedly copied. "The Claimants cannot avoid the consequences of their submission and the way the case is presented," he wrote.

"Equally it seems to me that if I reject their submission that the Central Theme as put by them is the Central Theme of HBHG it cannot be said that even if Mr Brown copied it that he has thereby copied HBHG or a substantial part thereof."

And later: "It seems to me … that the Central Theme is not a genuine Central Theme of HBHG and I do no (sic) accept that the Claimants genuinely believe it as such. In my view it is an artificial contrivance designed to create an illusion of a Central Theme for the purpose of alleging infringement of a substantial part of HBHG."

The one central theme that Justice Smith did identify in HBHG was the merger of the Merovingian bloodline with the Royal Bloodline of Mary Magdalene. "As such it is self evident in my view that is an idea which is of a too general level of an abstraction to be capable of protection," he wrote. "Nor is there any architecture or design in HBHG if that were the theme which can be said to have been appropriated. The Claimants simply do not reveal how they came to their idea or conjecture as they prefer to call it. It not being revealed it cannot be appropriated."

Drawing on other cases, Justice Smith observed: "When a book is put forward as being a non fictional book and contains a large number of facts and ideas it is always going to be a difficult exercise in trying to protect against copying of those facts and ideas because as such they cannot be protected. It is the effort and time that has gone into the way in which those ideas and facts are presented that is capable of protection."

Justice Smith dismissed the Claimants' action.

Lee Curtis, an intellectual property specialist with Pinsent Masons, the law firm behind OUT-LAW.COM, said the ruling came as "no surprise to lawyers and authors."

He added: "Had the judge found in favour of Baigent and Leigh, it would have gone against the premise of copyright laws and sent shockwaves throughout the legal and literary worlds."

Pointing out that copyright protects the expression of an idea, not the idea itself, Curtis added, "Brown didn't infringe copyright in the earlier book, he just created a new expression of its idea."

Baigent and Leigh face paying their own legal costs plus 85% of Random House's legal costs. Their total bill has been estimated by The Times at £2 million.

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