I

Imitation: A fugal technique of composition, in which one part introduces a theme, or subject which is then answered by the other parts by reitorating the same theme later in the work. This term is usually applied to fugal passages in choral music.

Imperfect Cadence: See half-cadence.

Impressionism: A stylistic period of composition that sought to put into music the most immediate, direct impressions, upon the composer, of a given subject. Impressionism avoided traditional harmony of thirds, employing more often quartal or quintal tonality.

Impromptu: A short, improvisational-sounding piece.

Improvisation: Spontanious composition. The performance of music that is composed on the in the moment by the performer, usually as a solo, or cadenza. Also used extensively in Jazz.

Incidental Music: Short musical segments that accompany, or highlight dramatic moments in, a play, or other stage work.

Instrumentation: The art of composing, orchestrating or arranging works for an instrumental ensemble.

Interlude: Short music used to bridge the acts of a play, or the verses of a hymn.

Introduction: The preparatory section, movement, or phrase of a musical work.

Interval: Intervals are what musicians use to describe the distance between any two notes. Go to Intervals Article to get a more exact description.

Introit: "Entrance". A psalm sung at the start of the Roman Catholic Mass.

Invention: A short, contrapuntal piece.

Inversion: The different forms that a chord may take by changing the chord member that is the bassof the chord.

Invertible Counterpoint: counterpoint in which two or more voices can be interchanged for one another.

Ionian Mode: A medieval mode whose scale pattern is that of playing C to C on the white keys of a piano. This scale is identical to a major scale.

Italian Sixth Chord: An augmented sixth chord, which contains a only three tones, as opposed to a German Sixth Chord, or a French Sixth Chord.