Funnily enough, the word orthoepy (or orthoëpy) meaning “(the study of) correct (or standard) pronunciation” has no single established correct pronunciation: it may be stressed on either the first or the second syllable (there is also variation in the pronunciation of the vowel in the penult syllable).
I’m curious about how the variant with stress on the first syllable originated, and how it has been justified by the orthoepists who have favored it. (A Wordnik blog post by Charles Harrington Elster, the author of “The Big Book of Beastly Mispronunciations”, seems to say that he favors the first-syllable stress only because “authorities have ... long countenanced” it and because he thinks it better emphasizes the root “ortho”; this seems like a lame explanation to me.)
The earliest source I am familar with that describes this pronunciation is John Walker’s Critical Pronouncing Dictionary (1824). Walker says it is accented on the first (pre-antepenult) syllable, citing Elphinston and Nares (p. 429). It’s not clear from his respelling system whether he means for the penult syllable to have secondary stress and a long vowel (/i:/) or no stress and a reduced vowel /ɪ/, as Walker seems to transcribe both of these sounds as e².
In an earlier section about general principles of stress placement in compounds derived from Greek he gives the following odd justification for this stress pattern: “Orthoëpy, having no consonant in the antepenultimate syllable, naturally throws its accent on the first” (p. 54).
I don’t understand why this seemed “natural” to Walker. Walker loved analogies; are there any other Greek compound words where this happens that I’ve missed? I actually can only think of counterexamples, such as psychiatry.
In fact, I wasn’t able to find any other Greek-derived or Latinate words of any type ending in "V.VCy" that had stress earlier than the antepenult. There are a lot of words like sponta’neity with antepenult stress on a vowel in an open syllable. I did find polyploidy, haploidy, diploidy but in these words the “oi” is pronounced as a diphthong rather than as two vowels in hiatus, so they don’t really seem to have the same structure. (I also found the words breviary and zedoary, but I disregarded these as they end in the suffix “-ary” < Latin “-arium/-aria/-arius” and words with this suffix tend to follow different principles of stress).
I realize this question may seem to be a matter of opinion. But, I don’t actually want an answer that describes your preferred pronunciation. I want to learn facts relevant to the pronunciation of this word, in particular:
whether there are any words that back up Walker’s idea that antepenultimate syllables that don’t have a consonant after them are less likely to be stressed
whether any of Walker’s contemporaries or precursors gave a different explanation for why this word is, or should be stressed on the first syllable.
I don’t think these are matters of opinion. Also, note that this is not a duplicate of either of my previous questions about the position of stress in specific other words, Why does "stigmata" [often] have penult stress? and Can the stress pattern of "uroboros/ouroboros" be explained by any principle, or is it random? Those questions were just open-ended “why is this word stressed this way” questions; in this question I’m specifically focusing on the two points listed above (if there are any analogous words with the same stress pattern, and whether anyone discussing the pronunciation of this word in the past gave another justification than the ones Walker and Elster give).
Answer
Looking at words beginning with ortho- there seem to be two possible pronunciations:
/ɔːrˈθɒ-/ as in orthogonal or orthography,
/ˈɔːrθə-/ as in orthodox or orthodontist,
where the second pronunciation has primary or secondary stress on the first syllable.
But in English phonology, the vowel /ɒ/ must be followed by a consonant, so the first pronunciation is ruled out for orthoepy. This is presumably what Walker meant when he said “Orthoëpy, having no consonant in the antepenultimate syllable, naturally throws its accent on the first” (1822).
You could also pronounce orthoepy /ɔːrˈθoʊ.iː.pi/. This seems to be what Robert Nares meant when he said that "the accented vowel is long in the antepenultima" (1782). However, there aren't any other words where ortho- is pronounced this way. I suspect this discouraged people from using it.