Scales, Keys and Key Signatures
Scales are the ordered collections of pitches that give a passage of music its tonal flavor. Understanding how scales are built, how key signatures encode them, and how major and minor differ is essential for both analysis and composition.
Tones and semitones build scales
A scale is defined by its pattern of intervals. The major scale follows the sequence tone–tone–semitone–tone–tone–tone–semitone (T–T–S–T–T–T–S). Starting on C and following this pattern uses only the white keys of the piano, which is why C major has no sharps or flats. Start the same pattern on G and you must raise the seventh note to F♯ to keep the intervals correct; start on F and you must lower the fourth to B♭. This is why every major key except C requires accidentals, and why those accidentals appear predictably.