Sure. And all the overtones, etc.. The full diapason.
Maybe, but I don't tend to think so. Solfege is a system where the idea behind it is supposed to represent aural relationships between pitches. I tend to think of letter names as isolated names for notes almost strictly for the sake of verbal communication, and perhaps mental organization, but not related as much to sound as is solfege. Ti-Do indicates a particular polartiy, B-C doesn't, unless connected to the second thought to relate it in one way or another to Ti-Do. I'm sure you could make some form of argument in one way or another about that.
Either way, my question is not about letter names. And ultimately, I'm trying to better understand my own perception and organization of sound, especially that as a small child. It is important for me that I do, and neither letter names nor solfege were my system. However, solfege is more closely related.
See given that I never learnt solfege as a young student.. but did develop strong pitch/ear skills without it, I do not need to connect to a second thought about solfa to determine what B-C sounds like.. rather, I just look at B-C and have a hard time not imagining the sound directly from that.. Same from notation.. the pitch and relationship between pitches exists without any reference to solfa.. likewise I have a direct association with sound and piano key, without any thought toward letters/numbers/solfa etc.
Also, even though I understand solfa, I would see ti-do and have to relate that to the scale degrees, 7 - 1, then I would know what it sounds like. The solfa is aurally meaningless to me, its just a theoretical concept, and will remain that way unless I make a deliberate effort to make the mental associations.
Hence my position that the syllables, letters whatever is irrelevant.. there is a pitch skill, and you associate sounds to certain words/letters/syllables. Doesn't matter whether its solfa, letters, numbers, piano keys, guitar frets.. or something completely different again.
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Perhaps your question isn't really about solfa at all, just about sound organisation and how we relate pitches to one another.
Musically my pitch is relative, but not necessarily key based, rather just what ever note is sounding now I have a relative sense of potential future notes based on that, as opposed to relating to the root of a key always - so a kind of 12 tone chromatic relative pitch. Although I'm sure that is combined with a sense of key, because there is obviously a clear understanding of common diatonic progressions and I tend to like things to resolve to the tonic eventualy
But its also perfect or absolute in that there are obvious artistic differences between tones (or chords or keys - that have similar tonal qualities such as major or minor) that I can identify independently of any other sounds..
Strikes me as some kind of disorganised organisation.