The character [m] is a key part of the LAAFU puzzle. It consistently appears at the end of a word (95% of all occurrences) and regularly as the last character of a line (67% of all occurrences). Because it has a restricted distribution conditioned by the line of text, it is a LAAFU feature.
Though we do not know the ultimate cause of [m] distribution (and therefore of LAAFU) we can still investigate the character as a problem.What could make a character appear so often at the end of a line and less often away from that position?
Our starting point should be, as always, that any process which can generate a text the length of the Voynich manuscript, and with the apparent structure of words and lines, must work by a set of regular rules. The appearance of [m] at the end of lines is not simply random but for a reason inherent in the creation of the text. The best way to discover the reason (or at least how the creation process worked) is to make the text more homogenous. That is, how do we get the end of the lines to look like the rest of the lines?
Some time ago I discussed Grove words, which present a similar problem. It was clear that the semantic content of the text could not or would not cause words to take specific characters. There’s also no reason here why words with a particular meaning would sit at the end of a line.
Likewise, it is hard to believe that the word order would be so free as to let such words be moved to the end of a line. Indeed, lines ending [m] are most common in Quire 20 where the lines are longest and would demand the greatest freedom of word order.
As with Grove words—as with other LAAFU effects—it is easiest to imagine that transformations are made to words already in a given position. So, for example, Grove words and linefirst words have characters added to the beginning of an existing word. The same could be adding [m] to the end of words at the end of lines which are valid without that character.
Yet in some words [m] is preceded by [i], an unlikely word ending which would be the outcome were the [m] removed. It is thus more reasonable to propose that the final character of a word is transformed into [m] when that word occurs in certain environments, one of which is the end of a line.
So we are left with the question: if another character is transformed into [m], which character is that? Even if we are only accepting this transformation as a working hypothesis, we should seek to identify the best fit character.
Below are some considerations.
What Comes Last
Because [m] occurs mostly at the end of words, it can only be replacing a character which also appears at the end of words. The character doesn’t have to only appear in that position, however, as the word–final occurrence could be a condition of what causes [m].
The most common word–final characters are, in descending order (with percentages): [y] 40%, [n] 16%, [l] 16%, [r] 14%, [s] and [o] with 3% each, and [d] with 2%. Given that [m] itself makes up 3% of all word–final characters, and that it is unlikely to effect a majority of all instances of a character word–finally as it occurs mostly at the end of a line, we can guess that [y, n, l, r] are the most likely candidates.
What Comes Next Last
We mentioned above that sometimes the character [i] comes before [m], which is does in about 70 tokens. It is one of just a few characters which come before [m], the percentages of which are: [a] 71%, [o] 18%, and [i] 6%. All other characters total less than 5%.
Given that [y] doesn’t occur much after any of these three characters we can rule it out as a candidate. The percentages for [n, l, r] are as follows:
Before [n]: [a] 2%, [o] <1%, [i] 97%
Before [l]: [a] 31%,  56%, [i] <1%
Before [r]: [a] 45%, [o] 39%, [i] 10%
We can see two things instantly: [n] is a bad candidate because it occurs almost exclusively after [i], and that neither [l] nor [r] are perfect fits. From these statistics it would seem [r] is the best fit, but not convincingly near.
Where Does It Come?
Earlier we said that two thirds of all [m] occur at the end of lines. The total number of tokens is about 780. Any character which is transformed into [m] word and line finally should show a distinct drop in occurrences in that context.
The curious truth is that all three of [n, l, r] show lower occurrences word–finally at the end of a line: [n] is 2.5% points lower, [l] is 4.5% lower, and [r] is 6.5% lower. The character [r], with the greatest drop, would seem once again to be the best candidate.
However, [m] is more than 13% points higher at the end of the line, twice the amount by which [r] drops. Indeed, it is about equal to the total drop of all three characters.
The character [y], which we have already dismissed as a potential candidate, does not change in frequency at the end of the line.
What Does It Look Like?
Although we cannot be sure that the strokes from which Voynich characters are composed are meaningful, we have seen some indication of that. The conditioning environment for [y] becoming [a] is the following character containing a short stroke like [i]. Likewise, we have seen patterns in the occurrences of gallows and their composition. It is reasonable to consider whether [m] bears any similarity to our three candidates.
All three characters, [n, l, r] contain the same short [i] stroke which [m] contains. Also, all three have an additional stroke emerging rightward from the character, much as [m] does. However, [n] has the rightward stroke emerging from the bottom of the [i], whereas [l, r, m] have it emerging from the top.
The rightward stroke of [m] follows a more similar course to [r] than [l]. Whereas the rightward stroke of [l] quickly turns down and leftward, crossing the [i], in [r] and [m] the rightward stroke continues right before turning up and leftward. For [r] the stroke continues leftward, while in [m] it dives down and rightward through its earlier path.
Once again, the best match for [m] in graphical terms is [r].
What Words Do We End Up With?
Our goal, mentioned at the start of this post, is to attempt to ‘restore’ the text to its state before [m] was present. We meet success if the text becomes more regular and thus one step nearer to its creation process.
If we take [r] as the best fit for [m], and change all instances of [m] to [r], what words do we end up with? And do they resemble existing words for [r]?
The short answer is: somewhat.
It is certainly true that a common word ending with [r] tends to be paralleled by a common word ending with [m]. So, for example, [dar] accounts for nearly 6% of all words ending with [r], and [dam] for about 9% of all words ending with [m].
Not perfect, but for most words where [r/m] is preceded by [a] the percentage for [m] is higher, while for those preceded by [o/i] it is lower. Also, there are a number of instances of words ending [ram] which are barely paralleled by words ending [rar].
The character [m] may well be a word and line final variant of another character. If this is so then the best character fit is [r]. However, the fit is not perfect.
The underlying reason for the occurrence for [m] is unknown, but the hypothesis that [m] is a variant of [r] gives us a point from which we can explore further. One specific question is why [r] still occurs word and line finally, and why only a portion of that character is transformed into [m]. Research into the specific environments of these two characters at the end of lines may reveal differences which take us further toward the ultimate cause.