Aleatoric music
A compositional principle with deliberately deployed elements of chance.
What it means
Aleatoric music denotes compositional procedures in which chance plays a definite role. The name derives from the Latin word for dice. Two areas are to be distinguished: chance in the making of the notated text, for instance when successions of notes are determined by a random procedure, and chance in the performance, when the performers decide on the order, duration or repetition of sections. In the second case one also speaks of open or variable form.
In the notation
Such works often work with graphic elements: fields of material to be played in a selectable order, paths through the score, time indications in seconds instead of bars, latitude for pitch and duration. The preface as a rule contains precise instructions on what is fixed and what remains free; without these indications the score cannot be performed.
Musical use
The procedures belong to the music since the middle of the twentieth century and stand in connection with a changed conception of the work: not every performance need be the same, and the performers are given a share in the shape. Frequently the freedom is precisely bounded, so that chance operates within a clearly staked frame — the sound colour of a work thereby stays recognisable even when the sequence changes. From the musical dice game of the eighteenth century, aleatoric music differs in its intention: there it was a matter of a game with finished building blocks, here of the form itself.
Performance practice
Read the preface in full before you practise; without knowledge of the rules any preparation is in vain. Settle a version for the performance and write it down, so that rehearsal work is possible. Clarify within the ensemble who makes which decisions and how transitions are signalled. Practise the shaping of time with a clock when there are indications in seconds. Treat free passages as precisely as notated ones — freedom does not mean arbitrariness.
Remember that chance in the performance does not suspend responsibility: whoever chooses among several possibilities makes an artistic decision and should be able to justify it. It helps to try out several versions and compare their effect before one is fixed. With works using graphic elements it is worth setting one’s own reading down in writing, so that later performances can build on it. In the programme a brief note on the procedure is fitting, because otherwise the audience suspects arbitrariness where a considered frame stands.