Could "a" be a ligature?

[pfeaster]

The idea that [a] = [ei] is fairly widespread, I think.  One point in its favor is that there are so many ambiguous cases that can't be resolved clearly as either [a] or [ei], but instead fall somewhere in between.  If there were a meaningful distinction between [a] and [ei], these cases should have caused confusion (I'd argue that the absence of any radically stylized forms for common vords suggests that such distinctions couldn't generally be worked out from context).  But apparently these cases didn't cause a problem (presuming Voynichese "worked").

For what it's worth, I suspect that [oi] and [ai] might also be interchangeable, on similar grounds, with [oi] being more deliberate and [ai] hastier or more cursive.  If so, this could point to a dynamic in which the beginning of a line was slower and more laborious to encode (so that [oi] is more common there), while the later part of a line "fell into place" as the ending was reached (so that [ai] is more common there).  I mean this to include cases with flourishes attached, e.g. [ar]/[or], [al]/[ol], etc.  But I don't mean to suggest that [a] can be substituted for any [o] -- just an [o] followed by [i], with the anticipated [i] influencing the form of the second stroke of the [o].

Meanwhile, word-final [o] and [b] seem likely to be interchangeable as well, with [b] = [e*] and [n] = [i*] where [*] is a particular flourish.  The variation between [o] and [b] would then be analogous to the variation between "closed" and "open" forms of [n].  But I'm not sure how to reconcile that with [oi] = [ai].