A Unison is 1/1
An Octave is 2/1
An Octave and a Fifth is 3/1
A Perfect Fifth is 3/2
A Perfect Fourth is 4/3; however, "4" is not a prime
number. The accurate description of a Perfect Fourth is 2X2/3
("X2" meaning up one octave).
Since a lower prime number always represents a sound wave to
which the wave represented by the higher number will act in a
subservient way, we can define the top note ("2" up
an octave) in the fourth as the tonic with the bottom note ("3")
functioning as the fifth.
Esoterically speaking, either note can be viewed as the tonic
- it depends upon which tonal structure you set up in your mind.
If you view the bottom note in the fourth as the tonic of its
own key, then the top note will have extreme "distance" as
the lower prime number (2) is exerting a lot of pull. It wants
to be the tonic - to make the lower note (3) subservient. The
brain naturally identifies the top note as the tonic (lower prime
number) with the bottom note being close in distance. Our educational
training, however, has identified the bottom note as the tonic
with the top note being considered a consonant Perfect Fourth.
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