To elaborate, intervals in the harmonic series are not arbitrary because the frequencies of the two notes forms a ratio: 2:1 octave [1] 3:2 perfect fifth [

To elaborate, intervals in the harmonic series are not arbitrary because the frequencies of the two notes forms a ratio: 2:1 octave [1] 3:2 perfect fifth [2] 4:3 perfect fourth [3] [1]: https://en.wikipedia.org/wiki/Octave https://en.wikipedia.org/wiki/Octave [2]: https://en.wikipedia.org/wiki/Perfect_fifth https://en.wikipedia.org/wiki/Perfect_fifth [3]: https://en.wikipedia.org/wiki/Perfect_fourth https://en.wikipedia.org/wiki/Perfect_fourth