English adventurer Edward Kelley may have concocted the document to defraud Rudolph II, the Holy Roman Emperor.

Other features of Voynichese, however, are not so easily reproduced. For instance, some characters are individually common but rarely occur next to each other. The characters transcribed as a, e and l are common, as is the combination al, but the combination el is very rare. This effect cannot be produced by randomly mixing characters from a table, so Stolfi and others rejected this approach. The key term here, though, is "randomly." To modern researchers, randomness is an invaluable concept. Yet it is a concept developed long after the manuscript was created. A medieval hoaxer probably would have used a different way of combining syllables that might not have been random in the strict statistical sense. I began to wonder whether some of the features of Voynichese might be side effects of a long-obsolete device.

The Cardan Grille
It looked as if the hoax hypothesis deserved further investigation. My next step was to attempt to produce a hoax document to see what side effects emerged. The first question was, Which techniques to use? The answer depended on the date when the manuscript was produced. Having worked in archaeology, a field in which dating artifacts is an important concern, I was wary of the general consensus among Voynich researchers that the manuscript was created before 1500. It was illustrated in the style of the late 1400s, but this attribute did not conclusively pin down the date of its origin; artistic works are often produced in the style of an earlier period, either innocently or to make the document look older. I therefore searched for a coding technique that was available during the widest possible range of origin dates--between 1470 and 1608.

A promising possibility was the Cardan grille, which was introduced by Italian mathematician Girolamo Cardano in 1550. It consists of a card with slots cut in it. When the grille is laid over an apparently innocuous text produced with another copy of the same card, the slots reveal the words of the hidden message. I realized that a Cardan grille with three slots could be used to select permutations of prefixes, midfixes and suffixes from a table to generate Voynichese-style words.

A typical page of the Voynich manuscript contains about 10 to 40 lines, each consisting of about eight to 12 words. Using the three-syllable model of Voynichese, a single table of 36 columns and 40 rows would contain enough syllables to produce an entire manuscript page with a single grille. The first column would list prefixes, the second midfixes and the third suffixes; the following columns would repeat that pattern. You can align the grille to the upper left corner of the table to create the first word of Voynichese and then move it three columns to the right to make the next word. Or you can move the grille to a column farther to the right or to a lower row. By successively positioning the grille over different parts of the table, you can create hundreds of Voynichese words. And the same table could then be used with a different grille to make the words of the next page.

I drew up three tables by hand, which took two or three hours per table. Each grille took two or three minutes to cut out. (I made about 10.) After that, I could generate text as fast as I could transcribe it. In all, I produced between 1,000 and 2,000 words this way.

I found that this method could easily reproduce most of the features of Voynichese. For example, you can ensure that some characters never occur together by carefully designing the tables and grilles. If successive grille slots are always on different rows, then the syllables in horizontally adjacent cells in the table will never occur together, even though they may be very common individually. The binomial distribution of word lengths can be generated by mixing short, medium-length and long syllables in the table. Another characteristic of Voynichese--that the first words in a line tend to be longer than later ones--can be reproduced simply by putting most of the longer syllables on the left side of the table.

The Cardan grille method therefore appears to be a mechanism by which the Voynich manuscript could have been created. My reconstructions suggest that one person could have produced the manuscript, including the illustrations, in just three or four months. But a crucial question remains: Does the manuscript contain only meaningless gibberish or a coded message?

I found two ways to employ the grilles and tables to encode and decode plaintext. The first was a substitution cipher that converted plaintext characters to midfix syllables that are then embedded within meaningless prefixes and suffixes using the method described above. The second encoding technique assigned a number to each plaintext character and then used these numbers to specify the placement of the Cardan grille on the table. Both techniques, however, produce scripts with much less repetition of words than Voynichese. This finding indicates that if the Cardan grille was indeed used to make the Voynich manuscript, the author was probably creating cleverly designed nonsense rather than a ciphertext. I found no evidence that the manuscript contains a coded message.

This absence of evidence does not prove that the manuscript was a hoax, but my work shows that the construction of a hoax as complex as the Voynich manuscript was indeed feasible. This explanation dovetails with several intriguing historical facts: Elizabethan scholar John Dee and his disreputable associate Edward Kelley visited the court of Rudolf II during the 1580s. Kelley was a notorious forger, mystic and alchemist who was familiar with Cardan grilles. Some experts on the Voynich manuscript have long suspected that Kelley was the author.

My undergraduate student Laura Aylward is currently investigating whether more complex statistical features of the manuscript can be reproduced using the Cardan grille technique. Answering this question will require producing large amounts of text using different table and grille layouts, so we are writing software to automate the method.

This study yielded valuable insights into the process of reexamining difficult problems to determine whether any possible solutions have been overlooked. A good example of such a problem is the question of what causes Alzheimer's disease. We plan to examine whether our approach could be used to reevaluate previous research into this brain disorder. Our questions will include: Have the investigators neglected any field of relevant expertise? Have the key assumptions been tested sufficiently? And are there subtle misunderstandings between the different disciplines that are involved in this work? If we can use this process to help Alzheimer's researchers find promising new directions, then a medieval manuscript that looks like an alchemist's handbook may actually prove to be a boon to modern medicine.

GORDON RUGG became interested in the Voynich manuscript about four years ago. At first he viewed it as merely an intriguing puzzle, but later he saw it as a test case for reexamining complex problems. He earned his Ph.D. in psychology at the University of Reading in 1987. Now a senior lecturer in the School of Computing and Mathematics at Keele University in England, Rugg is editor in chief of Expert Systems: The International Journal of Knowledge Engineering and Neural Networks. His research interests include the nature of expertise and the modeling of information, knowledge and beliefs.

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