Did you know that you can play a melody starting on any of the twelve possible notes, while still preserving its melodic and harmonic character?
For example, you can play “Twinkle, Twinkle” starting on the note C…
But you can also play it starting on the note G…
In fact, you can play “Twinkle, Twinkle” (or any other melody) starting on any of the twelve available notes.
How Many Keys are There?
The answer to the question depends on whether you are talking about physical keys or theoretical keys. Since there are twelve possible physical keys on the piano, there twelve possible physical “keys” in which you can play a piece of music. But, while there are twelve physical keys, it is possible to write music with up to seven sharps or seven flats in the key signature, making at least fifteen keys theoretically possible, but do not worry about these things right now. In fact, you may never have to concern yourself with this quirk of music notation ever again. It is just mentioned for completeness sake.
That said, here is “Twinkle, Twinkle” written out in fifteen theoretical keys:
You will discover that Do will always sound-feel like Do, So will sound-feel like So, La will sound-feel like La, and so on… no matter what key you are in!
The main point here is this: When you start the melody on a different note (play in a different key), all of the letter names of the notes change, but the Solfege names remain exactly the same.
The letter names change because they are arbitrary, but the Solfege names remain the same because they symbolize the sound-feelings that are inherent in the melodic-harmonic function of each melody note, no matter what key you are in.
Mastering this concept is a critically-important step towards understanding how music really works.