In my last post, I made a proposal about vowels, and inadvertently revealed that I am not a real Voynichologist, because I referred to [p,f,t,k] as "tall, loopy letters" instead of using their conventional name: gallows letters.
First, consider the distribution of the gallows letters within words. The following graph shows the relative frequency of gallows letters compared to other letters in the first ten letters of Voynich words:
Gallows letters are heavily represented at the beginnings of words, and scarcely represented later in words. If they represent vowels, then what does this imply? Perhaps the language has syllable stress, and the stress normally falls on the first syllable of a word, and only the stressed vowel is written.
That could not be the whole picture, however. In English, a language with a bias towards stressing the first syllable, the relative frequency of the vowels compared to other phonemes in the first ten phonemes looks like this (data from the Carnegie Mellon pronunciation database):
As you can see, stressed vowels are slightly over parity with other phonemes as the second phoneme of a word in English. To explain the gallows letters as stressed vowels, we would additionally have to assume some particular stressed vowel or vowels in the first syllable if no other vowel is written, and this would have to apply to about 4/5 words that are stressed on the first syllable.