vir litterarum wrote:So are you arguing that the stress accent of Latin is qualitatively different from that of English?
Just expand a little bit more on what others have already said:
It's not so much that the stress accent of Latin was qualitatively different from that of English (although it may have been). The main point is that vowel length in Latin was fundamentally different from what we call length in English. In Latin, a long vowel was always
pronounced twice as long as the corresponding short vowel, regardless of the position in the word or whether it was stressed or not. That was the only
difference in the sound of the two vowels.
As you can see, the relationship between the "long" and "short" vowels in English is nothing like this. It is simply a historical accident that we even use the terms "long" and "short" for something that is a fundamentally different phenomenon. The example that you mentioned, "breed" and "bred," does not involve long and short versions of the same vowel. They are two different vowels (which just happen to be spelled the same). As described phonetically, "breed" contains a "high unrounded front vowel," whereas "bred" contains a "mid unrounded front vowel with lax articulation" -- i.e., not only is the front part of tongue lower in the mouth, but there is also slightly less tension in the throat muscles; you can see this x-ray videos of people pronouncing sounds. The same holds true for other vowels that we call long and short versions of each other, but they are really not. In fact, most English vowels do come in pairs of "tense" and "lax," but often these don't match up with what we call long and short. E.g. "oo" as in "boot" and "u" as in "put" (at least in American English; the pairs are different in other varieties of English). In all these cases, the actual period of time that it takes to articulate the vowel is completely incidental to the distinction in sound; length, as I mentioned before, correlates almost entirely with 1) stress, and 2) whether the following consonant is voiced or voiceless.
The upshot of all this is, in Latin, vowel length (and likewise syllable length) must have had much much greater acoustic prominence than did stress. Whatever Latin stress sounded like, it must have been comparatively weak in the classical period; and that is why it was natural for them to base their meters on quantity instead of stress. Since the phonology of English is completely different in all respects, quantity-based meters simply don't work for us.