Phonology of Voynichese

[Stephen Carlson]

Hulden defines the obligatory contour principle (OCP) as "a universal cross-linguistic tendency to avoid redundancy or repetition of similar speech features within a word or morpheme, especially if the phonemes are adjacent to one another".
The principle is that characters that tend to occur consecutively must have different sounds, while characters with similar sounds never or very rarely appear next to each other. At the light of this, it seems clear why q- and -in end up being considered similar: they never appear in consecutive positions. Similarly, gallows do not appear consecutively, so they must be similar sounds. 
The positional constraints of Voynichese are so strong that they make several consecutive combinations impossible or very rare: this could contribute to make the lower splits in this tree unreliable (because they depend on ridiculously small numbers). On the other hand, some of those constraints may very well be a consequence of the OCP.

Any analysis based on the OCP (which is admittedly a pretty strong cross-linguistic tendency) would have trouble accepting EVA-i as a speech feature, because it is often doubled and tripled up. This is why Hulden's analysis split them up. At any rate, the EVA-i is reminiscent of the minim and may just represent a stroke rather than a letter, making the real symbols EVA-in and EVA-iin, as in the analysis.

Alternatively, if the OCP violations can diagnose non-linguistic behavior, then maybe repeated EVA-e and EVA-i are numerals.