DESCRIPTION:
In Five Songs (1956-57) and Muzyka żałobna (1958) Lutosławski introduced his own brand of twelve-tone music, marking his departure from the explicit use of folk music. His twelve-tone technique allowed him to build harmony and melody from specific intervals (in Muzyka żałobna, augmented fourths and semitones). This system also gave him the means to write dense chords without resorting to tone clusters, and enabled him to build towards these dense chords (which often include all twelve notes of the chromatic scale) at climactic moments. Lutosławski's twelve-note techniques were thus completely different in conception from Arnold Schoenberg's tone-row system, although Muzyka żałobna does happen to be based on a tone row.This twelve-note intervallic technique had its genesis in earlier works such as Symphony No. 1, and Paganini Variations.

n works from Jeux vénitiens, Lutosławski wrote long passages in which the parts of the ensemble are not to be synchronised exactly. At cues from the conductor each instrumentalist may be instructed to move straight on to the next section, to finish their current section before moving on, or to stop. In this way the random elements within compositionally controlled limits defined by the term aleatory are carefully directed by the composer, who controls the architecture and harmonic progression of the piece precisely. Lutosławski notated the music exactly, there is no improvisation, no choice of parts is given to any instrumentalist, and there is thus no doubt about how the musical performance is to be realised.

For his String Quartet (1964), Lutosławski originally produced only the four instrumental parts, refusing to bind them in a full score, because he was concerned that this would imply that he wanted notes in vertical alignment to coincide, as is the case with conventionally notated classical ensemble music. The LaSalle Quartet, however, specifically requested a score from which to prepare for the first performance. His wife Danuta solved this problem by cutting up the parts and sticking them together in boxes (which Lutosławski called mobiles), with instructions on how to signal in performance when all of the players should proceed to the next mobile.In his orchestral music, these problems of notation were not so difficult, because the instructions on how and when to proceed are given by the conductor.

Lutosławski's called this technique of his mature period "limited aleatorism".This controlled freedom given to the individual musicians is contrasted with passages where the orchestra is asked to synchronise their parts; the score for these passages is notated conventionally using bars (measures) and time signatures.