Have you ever wondered why there's an F# note in a G major scale? Or why an F major has a Bb? And why is it named Bb and not A#?!
Well, it will depend entirely on the musical 'context'. What that means is what 'key' the music is in. Musical keys are created from major scales, and so a solid understanding of why sharps and flats appear in certain major scales is so essential to develop our understanding of melody and harmony.
A 'key signature' consists of a certain number of sharp or flat notes that the music will contain. These sharp or flat notes are derived from respecting major scale formula and the rules of a diatonic scale.
Remember that the major scale formula is Tone-Tone-Semitone-Tone-Tone-Tone-Semitone (or for all you guys in The States - Whole step-Whole step-Half step-Whole step-Whole step-Whole step-Half step). A little more than that, each letter of the musical alphabet will appear in order (so, if we're thinking about a G major scale the first note will be G followed by A B C D E and F).
In this video lesson I will show you exactly how sharp and flat notes appear in scales and why these notes can only have one name.