Unmeasured prelude (prélude non mesuré)

A type of keyboard prelude unique to 17th-century French music in which the piece is notated entirely in whole notes with no bar lines, time signature, or durational indications other than slurs or ties. The performer is given complete freedom to interpret the rhythm, creating a spontaneous, improvisatory effect. Louis Couperin is the most important composer of these pieces: he left about thirteen, ranging from brief key-establishing preludes to the extended, harmonically adventurous Prélude in B minor. The notation derives from lute tablature practice and reflects the French practice of préluder — improvising a prelude before a formal piece.

Learning an unmeasured prelude is fundamentally different from learning a normal piece of keyboard music. There is no fixed rhythm to learn — the slur marks indicate phrasing and harmonic groupings, not duration. Begin by playing the whole notes as chords, slowly and deliberately, hearing each harmony before moving on. Then apply duration freely: long notes where the harmony is rich and resonant, shorter notes where the music moves purposefully. Listen to several different performances and notice how radically they differ: this is correct. The goal is to sound as if you are improvising the piece in the moment.