E as a Scale Degree

E is the third degree of the C major scale, called Mi in movable-doh solfège, and its distance from the tonic C is what music theory calls a major third, the interval that gives a major triad its characteristic bright quality as opposed to the minor third that would instead produce a minor chord. This single interval, whether the third above a chord's root is major or minor, is the primary acoustic distinction Western tonal harmony uses to separate music generally perceived as bright or sad, a foundational fact of the tuning system rather than an esoteric claim of any kind.

E also names the lowest and highest strings on a standard tuned guitar and is a common open string pitch on the violin family, practical facts of instrument design that have shaped an enormous amount of Western popular and classical music written to sit comfortably in keys related to E, entirely independent of any correspondence system.