If in original texts there were no means of distinguishing whether u and i were consonants or vowels, how then do we now know which ones were which?
The easy ruleset I learned in high school is that it is pronounced as a consonant if:
- It succeeds the letters q, g, or s and precedes another vowel
- It lies between two other vowels
- It lies at the beginning of a word before another vowel, except where this breaks rule 2
However, in my further research, which largely involved manually checking all combinations in which u or v was written in a word list extracted from Whitaker's Words, I found that it is recognized as a vowel:
- When u succeeds a consonant and precedes a vowel, except for the consonants q, g, s, and usually l or r:
- when l or r succeeds another consonant,
- when l or r lies at the beginning of the word,
- when l or r ends the 3rd principal part of a verb,
- and in the words miluus and beluus.
Otherwise, it is probably a consonant.
There are likely a few holes in this description, but I think this should account for at least around 90% of cases. Back to the question, these patterns of consonants and vowels were deduced solely from the already completed work of others, so how did they know which were which?