It might have come from my head. I've looked in the core books and I haven't found a reference. I put the questions here, because I thought there might have been a rule involved. As it seems open enough to interpretations like those above (all of which are interesting), maybe I should have posted in general discussion. In fact, [Mr Moderator, please] given where the next paragraph is going, that's definitely the case.
Both Atom's Old/Arcane Draconic and the tonal concept brought up (appropriately enough) by Tonguez are similar to thoughts I'd been having but I wanted to check with the rules before developing the central idea I'd been playing with.
Which is this:
Dragons frequently leave the survival of their offspring to fate. While some mature dragon pairings, especially good ones, tend their young to some extent, most wyrmlings are on their own from the moment they hatch. It makes you wonder how much more for their young even the good, mature dragons do.
Dragons have phenomenal intelligence. So how does a solitary wyrmling learn Draconic? Simple. It invents it. It is inherently aware of a need to codify its environment and it sets about trying to do so automatically. The rest is evolution, physiology, magic itself - and that intelligence. The structure of Draconic is fluid and multi-dimensional. Every dragon ends up speaking a unique dialect of it. This framework can incorporate both Atom Smash's and Tonguez's ideas. The Draconic that dragons speak is what the rest of the world calls High Draconic.
And what about yer kobolds and lizardmen and troglodytes and even humans? The reptilians speak a form of pidgin Draconic, which is taught to each new generation. It is far more limited in scope than High Draconic.
To give a poor example of the kind of thing:
Dragons can say, "4 x 2."
Kobolds can understand but only yap a clumsier, "2 + 2 + 2 + 2," to prove it. Even then, their diction is appalling. Pidgin Draconic has fewer tenses and cases as well, making speakers of it a whole bunch less articulate.
The Draconic that comes from Speak Language or a bonus language is more sophisticated than the corrupted utterances of the reptilians. It has something of the morphic aspect of High Draconic (hence the potential for spell research) but it's still more rigid than High Draconic.
The verbal components of spells cannot simply be Draconic fragments learned by rote though, because were that the case, you might think it reasonable to give anyone who can speak the language a free shot at identifying spells (as the spellcraft skill). But, if you take the idea of Draconic being the language of magic and the idea that everyone speaks a slightly different version of it, it does tie in well with the reasons for spellcraft checks.
I'm not sure where all this is going but I was looking around for campaign themes and these ideas kept niggling. I wondered if the connection between Draconic and wizardry had been clarified somewhere.
Can anyone tell me if the Draconomicon says anything interesting about Draconic?