Figure 3. A rank-frequency (Zipf's plot) of several texts: voynich (Friedman's first study group transcription), roget (Roget's Thesaurus), republic (Plato's Republic), Emma (Jane Austen), Alice (Alice in Wonderland, Lewis Carroll). Note that all, (except the Roget's Thesaurus which is a collection of very short definitions and cross referenced words) follow the same trend of a slope of -1 in the log-log plot. There are 2 more Zipf's "laws" which were also found in the Voynich manuscript (available at: http://web.bham.ac.uk/G.Landini/evmt/zipf.htm
It is possible that, if deciphered, the manuscript would reveal no more than the knowledge found in other mediaeval herbals and alchemy books. However, if the document is real it means that at least the people involved in the writing were able to read it. The fact that it still remains unread is quite unique and a challenge in cryptological terms. What was the method of encoding? What is the original underlying language ? Who wrote it? Why? It would also be interesting to know what kind of knowledge required such an amount of secrecy at the time of writing. It could even contain a subject completely unrelated to the drawings...
In any case, if a "readable" text is produced after some processing of the manuscript text, how can one be sure that the solution is correct? Could any of the solutions which have been announced be correct? On which basis to accept or reject a proposed a solution is quite a problem because there is no date, author, country or language associated with the manuscript. We will assume that:
1. there is a meaningful text underlying the writing in the Voynich manuscript
2. the language is a known one or closely related to a known one, and
3. the text is encoded using a reversible method.
Without all of these being true, there seems to be no possibility of finding a solution.
No solution which fails to present a detailed description of how the "encoding" was done by the writer(s) of the manuscript can be accepted, and this is where most of the proposed solutions fail. It is also clear that neither the method of encoding nor the contents of the decoded text may conflict with the context of a manuscript written in medieval Europe (or elsewhere by a medieval European). Finally, the solution should clearly explain the many odd statistical properties found in the manuscript text, which could not be fully described here, but which may be found in the literature on the subject (Tiltman, 1967; Currier, 1976; D'Imperio, 1978).
It seems paradoxical that at the time of rising concerns about the public use of "uncrackable" security codes, a medieval manuscript probably cannot be read. Let's hope that it is not for too long.