Why is τούς an oxytone but τοῦ is a perispomenon? The diphthong would seem to warrant a circumflex for the ultima of both.
If a word ends in …LS (that is, a L[ong] and then a S[hort] vowel), it can either be accented on the L or on the S. If the accent is on the L, that accent must be circumflex.
Example: ψῦχος.
But ψυχρός is not a violation, because its accent falls on the S at the end.
And the rule says nothing about either τοῦ or τούς, because they are not LS, but instead just L. Other examples of the same would be πούς and πῶς. And the rule says nothing about …SS either, ex. ὄνυξ or ὄνος or ὀπός.
If you’re wondering why the accents are different in this case, my understanding is that it’s because of how the endings were derived. τοῦ and τούς are like second declension nouns and adjectives which are accented on the last syllable, e.g. ἀγρός.
In an earlier stage of Greek, the genitive singular ending -σο was added to the stem ἀγρο, giving ἀγρόσο (the accent remaining on the same syllable as in the nominative - so I guess we’d have seen τόσο for the article, which at that time was a demonstrative I believe). Then the σ, as it was between two vowels, disappeared, and the vowels contracted: ο+ο = ου. As usual with contraction, the accent remained on the first part of the new vowel sound, so there’s a circumflex - ἀγροῦ and τοῦ.
In the case of τούς, it’s like ἀγρούς - here, the older ending was νς, so the forms were ἀγρόνς and τόνς. This time the ν disappeared, and compensatory lengthening took place - the ο lengthened into ου. Because this was lengthening rather than contraction, the accent stayed as an acute.
Thanks! I suspected it was a matter of lengthening or contraction but couldn’t find anything about the development of those articles. Did you just remember about τόνς or did you make use of a source that you can share? Again, thanks for this really helpful explanation!
No problem! The first 2 chapters of the Cambridge grammar cover these and similar issues, and there are some other explanations scattered elsewhere - see section 1.68 for τόνς. Unfortunately I don’t have anything with a detailed description of the development of the article - Palmer’s Greek Language has a couple of pages but that’s it.