"[2] For example, altered notes may be used as leading tones to emphasize their diatonic neighbors.
Similarly, in music in a minor key, composers and songwriters often "borrow" chords from the tonic major.
[10] According to composer Percy Goetschius, "Altered...chords contain one or more tones written with accidentals (♯, ♭, or ♮) and therefore foreign to the scale in which they appear, but nevertheless, from their connections and their effect, obviously belonging to the principal key of their phrase.
"[7] Richard Franko Goldman argues that, once one accepts, "the variability of the scale," the concept of altered chords becomes unnecessary: "In reality, there is nothing 'altered' about them; they are entirely natural elements of a single key system,"[11] and it is, "not necessary," to use the term as each 'altered chord' is, "simply one of the possibilities regularly existing and employed.
This means that the chord has the root, major third, minor seventh, and one or more altered tones, but does not have the natural fifth, ninth, eleventh, or thirteenth.
The notation of a raised fifteenth is a fairly modern addition to Western harmony, and they have been popularized by contemporary musicians like Jacob Collier.
Natural fifteenths are never notated as alterations or extensions, as they are enharmonically equivalent to the root.
To deal with this issue, bands with more than one chordal instrument may work out the alt chord voicings beforehand or alternate playing of choruses.
The choice of inversion, or the omission of certain tones within the chord (e.g. omitting the root, common in jazz harmony and chord voicings), can lead to many different possible colorings, substitutions, and enharmonic equivalents.