20th century compositional devices

extended chords

9th, 11th, and 13th chords

quartal harmony

stacked 4ths

quintal harmony

stacked 5ths

use of modes

use of any PADMIL modes or blues, hungarian minor, octatonic, whole tone, major and minor pentatonic, locrian, or acoustic modes

polychords

two chords sounding simultaneously (typically triads but can involve 7th chords too)

real planing

parallel chords that are literally transposed (i.e. all perfect 5ths, etc); note that planing must be marked with something defining the motion happening (i.e. triadic, quartal, quintal, chromatic)

tonal planing

parallel chords within a key; note that planing must be marked with something defining the motion happening (i.e. triadic, quartal, quintal, chromatic)

ostinato

repeated pattern

asymmetrical meter

meter with unequal subdivisions (i.e. 5/8); any meter defined by triangles and slashes

mixed meter

use of two or more meters in a row (i.e. alternating 7/8 and 5/8)

real polymeter

multiple meters happening at once and marked as so in music (i.e. 2/4 against 3/4)

implied polymeter

in the name, implying the presence of multiple meters happening at once but not marked as so, instead using articulation markings to imply the other meters

polytonality/bitonality

use of two tonal centers at once (i.e. one voice in CM, another in F#M)

isorhythm

repeated rhythmic cycles

isomelos

repeated pitch cycles

modes of limited transposition

modes that don't have 12 unique collections (i.e. whole tone, octatonic)

non-retrogradable (rhythms or melodies/harmonies)

palindromic set of rhythms/notes

rhythms with added values

measure with small, additional note (i.e. 4/4 with extra eighth note)

process music

music where a specific process determines structure of whole piece (i.e. messiaen's quartet for the end of time used rhythmic and pitch cycles in a very mechanical way to create the piece)

descant

counter melody above true melody

ametric music

music with no perceivable meter, no felt pulse

aleotoric music

music not bound by bar lines (typically seen as box around rhythm with squiggly line after)