When we assign numbers to the notes of the major scale of C*; the first note becomes 1, the second 2, the third 3, etc. In other words ‘c’ becomes 1, ‘d’ 2, ‘e’ 3, etc.
*note that the number system is a relative system that always refers to the 1 as indicated by the capital letter. 1 isn’t always ‘c’ like in this picture; as the 1 of the key of Ab major is ‘a flat’, the 1 of the major scale of G major is ‘g’ for example; and the 1 of an F chord is ‘f’.
The major scale of C is in essence notes 1 to 7. Note 8 is a new 1; it’s a new beginning of the next repetition of the same sequence. Like a new week starting on Monday!
Chord symbols use numbers from 1 to 13 however, spanning more than one repetition of the major scale sequence, to be able to distinguish a 6 from a 13, or a 2 from a 9 for example. In essence, the same notes yet in a different context.
There are names and numbers on the black keys in the picture above as well. The black keys represent the notes in between the originals.
Each black key has two names that derive from the white keys nearest to them – to the left and the right – plus either a # symbol along with the name of the tone to the left, or a b symbol along with of the name of the tone to the left.
This is a matter of perspective. It means the black key is seen as the nearest tone to the left that was raised by a semitone (the smallest possible distance between notes in the Western Tonal System), or it is seen as the nearest tone to the right that was lowered by a semitone.
For example F# = F sharp = an ‘F’ that was raised by a semitone as ‘#’ is the symbol for raising a tone by a semitone.
For example Bb = B flat = a ‘B’ that was lowered by a semitone as ‘b’ is the symbol for lowering a tone by a semitone.
Accidentals (#’s and b‘s) are also used in chord symbols in front of numbers, as you will soon see.
Accidentals in front of numbers in chord symbols not only indicate a raising or lowering by a semitone. They indicate a direction as well, a desire for movement in a particular direction: # stands for an upward direction, b for a downward direction.
For example #5 wants to become the nearest upwards note in the next chord while essentially the same note b13 wants to become the closest downwards note in a chord.
Instead of providing two kinds of numbers for the black keys, only some numbers are present in the picture of the keyboard above. These are the numbers commonly used in chord symbols. Numbers 8 and 14 are never used.
