For whatever daft reason, the current trend in modern Latin orthography is to write consonantal 'i' (IPA /j/) as 'i' rather than as 'j'. How can we then tell whether a given 'i' is a vowel or a /j/, especially considering that many dictionaries don't indicate this either?

I recognize that any set of rules for this will have exceptions (e.g., "māius" (greater) and "Māius" (of May) pronounce their I's differently), but there should still be some general usable way to determine this using little more than the spelling of the word in front of you.

  • Apart from some dictionaries, as noted below, marking all vowels, the only real way of knowing is memory.
    – cmw
    Feb 23, 2016 at 19:57

4 Answers 4


Dictionaries often explicitly mark long and short vowels, with a macron and breve accent, respectively. In such a dictionary, you will recognize a consonantic i from not having either accent: māiŭs¹. The same applies to consonantic u (if the dictionary doesn’t use v). This only applies to dictionaries that mark both short and long vowels explicitly; this is not a phonotactic rule about intervocalic i or u.

In general, the spelling alone is not enough to determine whether i or u, in a particular word, stands for the consonant or the vowel. This is a shortcoming of Latin orthography, comparable in English to the different spoken forms [riːd], [red] associated with the spelling read. For a Latin example, uoluit can be both uōlŭĭt (‘he wanted’) and uŏluĭt (‘he rolled’).

¹ It‘s actually uncertain whether the a really was long, but usually it is given like that in dictionaries.


Here are a few "rules of thumb" I use. I can't guarantee these will work in all cases.

  1. If you're an English speaker, look at a related English word from Latin. If it's spelled with "j," it was probably consonantal "j" in Latin as well. For example, we can compare Latin MAIVS to English "major," Latin OBIECTVM to English "object," and so on.
  2. Generally, derivatives of IACIO ("throw") are pronounced with /j/. There's a lot of them, so this is somewhat useful to know.

Another note: unlike most long consonants, phonetically long /jj/ was normally not written double in Latin. In addition, it seems that written I may have corresponded to /ji/ or /jji/ in some cases in words like TRAICIO "throw over" (composed of TRANS + IACIO). This means that you actually have to choose between five options for written i: /i/ /j/, /jj/ /ji/ and /jji/. (Or at least six if the source doesn't use macrons!)

Here is some of what W. Sidney Allen wrote about consonantal I in Vox Latina:

In the interior of a word, this sound rarely occurred singly between vowels. Where once it had been present, it was lost prehistorically (thus Latin trēs beside Sanskrit trayas). With a few exceptions noted below, whenever a single, intervocalic i-consonant is written, it stands for a double consonant, i.e. [yy]. Thus aio, maior, peior, Troia stand for aiio, maiior, etc. This is quite clear from various types of evidence. It is specifically mentioned by Quintilian and other grammarians, who also tell us that Cicero and Caesar used in fact to spell such words with ii (†Qu. i, 4, 11; †Priscian, K. ii, 14) and it is supported by frequent inscriptional spellings (e.g. PompeIius, cuiIus, eiius, maiIorem). In Italian a double consonant has been maintained in, for example, peggio from peius. Moreover, the consonant must be double in order to account for the fact that the preceding syllable is always metrically heavy; for the actual vowel is short—this is specifically mentioned by Ter. Maurus (†K. vi, 343), and is further evident from other considerations: e.g. maior is connected with măgis, being derived from măg-iōs.

(p. 39)

So it appears sources that use a macron in "māius" (greater) are assigning false quantity to the vowel; according to Allen, the actual pronunciation would have been /majjus/ with a short "a" and a long "j."

It appears that "Maius" was probably pronounced the same as "maius": with two syllables, the first long because of a following double /j.j/ sound. I'm not sure why you learned that they were different. In Italian at least, the modern pronunciation is indistinguishable from that of words that we know had intervocalic consonantal /jj/ (the Italian descendant of "Maius" is maggio). The etymology of "Maius" seems to be a bit unclear, but one hypotheses seems to be that it ultimately comes from the same root as maius.

Interchange between /j/ and /i/ in poetry

In poetry, words that usually have syllabic /i/ sometimes have /j/ instead. (Similarly, /u/ and /w/ are sometimes substituted for one another in poetry.) I don't know the details about when this can occur.

  • 3
    Another note: The i in Maius (the month) is not a separate vowel, either; the pronunciation could be the same as maius, or possibly ai could be a diphthong here. There is metrical evidence for this in Ovid’s Fasti, book 5, where the origins of the name are discussed: hinc sua maiores tribuisse vocabula Maio (v. 73); quarum Maia suas forma superasse sorores (v. 85).
    – chirlu
    Feb 24, 2016 at 0:28

In addition to Chirlu's excellent answer, although there is no hard rule, a rule of thumb does exist. If a syllable starts with an i and then a vowel other than i, the initial i is normally pronounced /j/; otherwise, it is pronounced /i/. When in doubt, the pronunciation can be inferred from the metre in verse.


Anlaut (word initial position):

i+V = >j+V, e.g. iubeo (in most cases)

but also i+V => i+V

  • only in some forms of the pronoun is (ii, iis) and the verb ire (iens, ii, ieram);
  • also in Greek loans (iambus, iaspis, iota, Io, Iones etc.)

Inlaut (word medial position):

In compounds and prefixed verbs

C+i => C+j adiacet

V+i => V+j seiungo

V+i+V => V+i+V only in very few examples

  • In Greek names: Achaia, Laius, Naiades, Troius, Acheloius, Minoius; Pleiades, Deianira; Nereius, Priameius, Achileius, Aeneius etc.;
  • In some adjectives: -uus, -uis followed by the comparative suffix –ior (strenuior, tenuior);
  • In some nouns

(adapted from Leumann 1977)

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