Rudiments There are twelve semitones to a complete octave, two semitones making a tone. The major diatonic scale has seven notes separated by the intervals of a tone (T) and semitone (S) in the sequence TTSTTTS. Each note has a separate letter name. In the scale of C major the most important intervals are C-E (major third), C-Eb (minor third), C-F (perfect fourth), C-G (perfect fifth); the triad CEG is referred to as chord I, chord DFA as chord II etc. In the diatonic major scale there are three major chords, I, IV and V; chords II and VI are minor and VII diminished.