@40Hz I mentioned this earlier but I'm still not sure about your exact take on this, so what do you think of this reasoning? (which is how I see it, I would like to know if it agrees with your philosophy)
1) Music/musicians are defined by roles, not by instrument
2) This role is defined by what they're playing, e.g. hitting rhythmatic low notes, playing full chords, arpeggios, melodic lines, counterpoint, and so on
3) However, different instruments are differently suited to different roles. The timbre of a synth bass sounds entirely different from that of a string bass; the timbre of a clarinet sounds entirely different from that of a saturated lead guitar, and so on. So for example, the "lead guitarist" (a role) can use his guitar with distortion pedals through a suitable amp (instruments) to play the role of a clarinetist in an ensemble, but he may not do a very good job of it depending on how closely he can nail the tone, phrasing, and so on (e.g. the fingering and physics of the guitar inherently creates a different phrasing as compared to the fingering and physics of a clarinet)
4) So while in theory, a bass guitar may also be used in a synth bass role, or a rhythm guitar role, or a baritone guitar role, and so on, a short scale bass is more likely to be suited to playing the latter roles than a long scale bass. And depending on the tuning of the strings, the thickness of the strings, the length of the neck and so on, the physics of the instrument may result in different fingering and 'feel' (e.g. how it feels when plucking/picking/strumming) that makes the instrument inherently more suitable for a particular rule.
And therefore, while strictly speaking, there isn't a "baritone guitar" or "short scale bass", there are instruments more suitable for playing the role of a "baritone guitarist" or "short scale bassist". I would guess that where I would most likely differ from you, if I'm reading your reasoning right, is that to me, if the instrument is really suitable for playing that role, then I'd just go ahead and declare "this is a baritone guitar". I mean, I'd expect that strumming chords on a short scale bass with thicker strings than a baritone guitar in a band setting would feel and sound like you're strumming a full scale bass, and not sit in the mix as well as compared to if you used an instrument set up for the baritone guitar role...
And this suitability could be on a few factors:
- whether it can reach the appropriate pitch
- timbre and note envelope of the instrument
- physical feel of the instrument when you play it, and how this suggests the appropriate phrasing for the part
Speaking of that last point, I once sessioned for a local production of a broadway musical and it was an interesting experience for me and the guitarist, since the parts were written on piano by a pianist, and the choice of notes and phrasing were stuff that's perfectly natural for a keyboard instrument but awkward on a normally-tuned guitar. But it was a great learning experience. Anyway, I was playing the role of a bassist, but perhaps I could have been playing the role of a piano left hand using a bass guitar to generate a different timbre.
Anyway, so far it's pretty abstract, but some concrete examples that might be a bit more relevant to the folks on talkBASS:
1) The bass guitar was originally created to take the place of the upright bass. But the technology allowed it to go in new directions. In addition, judging by the number of threads around here on "how do I make my bass guitar sound like an upright?", I'd say that the bass guitar and upright bass do play different roles because they're inherently different instruments. Although they can both be used in the same role (and a piccolo flute can't, since it doesn't have the same range of notes), because of timbre and feel and some undefinable mojo, the upright is less suited to playing full on metal just as the electric is less suited to playing old school swing, both genres created on those respective instruments and with the full weight of history and societal expectations behind them.
Of course, there's the caveat that if you really really wanted to, you could always use the upright for the metal bassist role and the electric for the old school swing bassist role, especially with some really good pedals and soundmen, but you probably wouldn't be doing the role as well as you could with the appropriate instrument. Same goes for baritone/short scale IMO, just that the line is a bit blurrer here.
2) And for me, personally, I play heavy rock and metal with a fretless, which is arguably an awkward instrument for the role as traditionally defined because it simply doesn't have the same timbre and tonal elements and the instrument suggests different fingering and phrasing, but I'm totally cool with my role as a "fretless bassist in a metal band".
I'd be totally cool with using a fretless baritone guitar in that same role, if I can get used to the fingering, but I don't know if I can find one that lets me tune down without the strings getting absurdly thick or the tension getting too low that it gets in the way of my playing, which then goes back to the same argument of certain instruments being more suitable than others.
The way I've phrased thing above might make it sound as though whether you nail the role or not is a binary, but I don't really think so. Like an instrument may be more suited for the role, and in your hands as a musician, you might get it so exact that no one can tell, or you might get close enough that the average listener can't tell and that's good enough, or you might not even get close at all but no one cares because it doesn't matter whether you're playing the bass clarinet role or the synth bass role. I think at the end of the day, choice of instrument, timbre, role and whatever else should be a conscious decision you make as a musician and you ought to be able to justify why you're picking an instrument, calling it a baritone guitar, and playing the role of a baritone guitarist in the band by choosing certain notes and phrasings.
Aaaaand. Some food for thought. Defining these roles, while fuzzy, still imposes some kind of categorization and we could always go into closer detail. Earlier I talked about roles not just as a "bassist" but as a "jazz bassist" or "metal bassist" and so on which then imposes certain requirements or expectations on the tone and phrasing and choice of notes... but what about if you're covering a particular band and you want to nail the exact tone of the original musician and play the parts note for note? Are you playing the role of, say, a "rock bassist" or are you playing the role of (whichever professional bassist originally recorded the song)? For that matter, when that bassist plays live, does he or she play it exactly the same way with the same tone as on the record? For example, I hear around the forum that it's pretty difficult to nail the bass parts on Muse records, and live, the bassist actually uses different instruments and instrumentation to get a similar sound and feel. Then, is he playing the same role as he played on the record?