I'm a complete beginner and trying to understand the basics of music theory these days. I guess I have a good ear and can play most songs by ear on guitar and piano and I'm sure this is a stupid question but I've noticed that any song can be played starting from any note, as long as the tone distances are kept the same.
Let's say the song starts with C,D,Eb (Tone,Tone,Half tone), it also sounds correct when E,F#,G (Tone,Tone,Half tone) is played.
I'm a bit surprised to discover that cause I used to think notes are not interchangeable. Am I missing something? Any suggestions?