What is viiii?

The viiii chord is a theoretical chord in music theory. It's built on the raised submediant (scale degree 6) of a major key. Because it's derived from outside the key, it's considered an altered chord.

Here's a breakdown:

• Construction: The chord would theoretically be a major triad built on the raised sixth scale degree. For example, in the key of C major, the sixth scale degree is A. Raising it would make it A#. Thus, a viiii chord in C major would be an A# major chord (A#-C##-E#).

• Function: Its function is debatable as it is rarely used due to its dissonant sound and unconventional placement in harmonic progressions. It could be theoretically analyzed as having a dominant-like function, leading to the tonic, albeit in a chromatically altered way.

• Practicality: Due to its awkward enharmonic equivalents (A# major is the same as Bb major which is far simpler to conceptualize), the viiii is almost always analyzed and notated as its enharmonic equivalent. For instance, in C major, the viiii (A# major) would be considered Bb major. Therefore, it's far more useful to think of it in terms of borrowing from a related key or mode, especially from parallel minor or closely related keys that already contain the flat seventh.

• Related Concepts: This concept is often encountered when discussing modal interchange or borrowed chords, which are standard techniques for adding color and interest to harmonic progressions. Understanding the theoretical viiii helps grasp the reasoning behind chromatic alterations.