Glossary

Idee Fixe
A French term coined by Berlioz, meaning 'fixed idea', and referring to a theme which is used recurrently throughout a work (such as his 'Symphonie Fantastique')
Idyll
A piece of music on a peaceful theme
Illustrative Music
See 'Programme Music'
Imitation
A technique in part-writing where one part imitates another. Canon and Fugue are special examples of this
Imperfect Cadence
See 'Cadence'
Impromptu
A short piece, often for piano, which is intended to sound 'improvised'
Improvisation
The art of spontaneous composition of a piece of music during performance, particularly used in jazz. The improvisation may be in the form of Ornamentation or a Cadenza
Incidental Music
Music written to accompany another artform, particularly a play. Also used of Overtures or Interludes
Infinite Canon
A canon which may be repeated for as long as desired, such as 'Three Blind Mice' or 'Frere Jacques'. Also known as a Round
Instrumentation
The selection of instruments for whicha piece of music has been composed. Also the act of deciding which instruments are to be used when composing or arranging a piece of music
Interlude
Music for performance inbetween acts of a play or other stage performance. Can also be used of any music written to be performed between sections of a formal piece of music (such as organ passages between verses of a Hymn)
Intermezzo
Italian for 'something in the middle', can mean an Interlude, or a piece of stand-alone music in the same style
Interrupted Cadence
See 'Cadence'
Invention
A type of two- or three-part contrapuntal composition for keyboard written by J. S. Bach
Inversion
The turning upside-down of a melody or chord, so that the top part or note moves to the bottom and vice versa