[_emacsomancer_]

> it's just the tonal contour of the original phrase, with the other details stripped out. I don't see how that differs from Punjabi syllables preserving their (originally) allophonic tone while losing their (originally) phonemic aspiration, such that the tone becomes phonemic.

because, as you elaborate, the English example you mention is really isolated - it's not enough to spawn a system of tone. Even in this case (the "I don't know" sequence), the tone isn't really contrastive.

> the phrase "I don't know" can't ever be a yes/no question

Sure it can, though the contexts wouldn't be that frequent. And some speakers have final rising tone even on non-yes/no questions.

> English has a non-vestigial system of grammatical tone at the sentence level

And of course there's more than just question-associated tone, there's also focus-associated tonal prosody.

[thaumasiotes]

> Even in this case (the "I don't know" sequence), the tone isn't really contrastive.

It's not contrastive in that there is no minimal pair that would demonstrate it. But good luck being understood if you don't produce it correctly. The lesson I would draw here is more "minimal pairs aren't sufficient to demonstrate every phoneme" than "it's not a phoneme until a minimal pair exists".

> the English example you mention is really isolated - it's not enough to spawn a system of tone

I didn't claim and don't believe that English is developing lexical tones. But I do believe that the development of lexical tone in this single unusual word is fundamentally similar to the larger-scale development of tone in other languages, and that the still-obvious relationship between the phrase and the tone sequence makes this a good example to help English speakers understand how it can happen.

> And of course there's more than just question-associated tone, there's also focus-associated tonal prosody.

Very true, but much harder to describe.

[_emacsomancer_]

> The lesson I would draw here is more "minimal pairs aren't sufficient to demonstrate every phoneme" than "it's not a phoneme until a minimal pair exists".

Perhaps. (Minimal pairs are, of course, simply a diagnostic tool.) It would be a pretty unproductive phoneme though.

> I didn't claim and don't believe that English is developing lexical tones. But I do believe that the development of lexical tone in this single unusual word is fundamentally similar to the larger-scale development of tone in other languages, and that the still-obvious relationship between the phrase and the tone sequence makes this a good example to help English speakers understand how it can happen.

I'm not deeply versed in tonogenesis - but that is interesting as a potential source (phrasal tone). I wonder what conditions could lead to phrase-related tonal patterns becoming prominent/frequent enough to be a source of more prototypical lexical tone.

> > And of course there's more than just question-associated tone, there's also focus-associated tonal prosody.

> Very true, but much harder to describe.

It's been discussed fairly extensively though, at least as far back as Jackendoff (1972 or thereabouts).