Universal key

The universal key or universal scale is a concept employed in music theory in which specific notes or chord symbols in a key signature are replaced with numbers or Roman numerals, allowing for a discussion describing relationships between notes or chords that can be universally applied to all key signatures.

For example, in the key of E-flat major, the notes of the scale would be replaced like so:
*"E" becomes scale degree 1
*"F" becomes scale degree 2
*"G" becomes scale degree 3
*"A" becomes scale degree 4
*"B" becomes scale degree 5
*"C" becomes scale degree 6
*"D" becomes scale degree 7

When used with chord symbols, the Roman numerals representing the roots are often written in upper case for chords in the major family, and in lower case for chords in the minor family, with the usual "m" or "—" minor chord delineator omitted outright:

*E becomes I
*Fm⁷ becomes ii⁷
*Gm⁷ becomes iii⁷
*Amaj⁷ becomes IVmaj⁷
*B⁷ becomes V⁷
*Cm⁷ becomes vi⁷
*D^ø7 becomes vii^ø7