Generative art refers to art that is constructed in part according to rules, to some degree outside the author's control. Rules might include mechanical systems, materials with independent behaviors (such as water flow or chemical reactions), mathematical procedures, huge data-sets, geometries and symmetries, and of course randomization.
Generative artworks have existed throughout human history. Before computing, composers used strict rule systems (the counterpoint of Bach, the serialism of Schoenberg) as well as chance (the dice-game of Mozart and chance operations of Cage). Pointilism, cubism, and other abstractions in painting are rule-based constraints. Many writers refer to Sol LeWitt's textual instructions, to be carried out by others; a direction more fully fleshed out with alternative approaches to scorewriting in music. One might also mention kinetic sculpture and generative texts (particularly the Oulipo group), or the pattern-based arts of Islamic tiling and weaving, Celtic knots, and other traditional arts.
The more it is considered, the more it seems that all art is somewhat generative, and certainly technological. (It is worth noting that the Greek term techné is the origin of both art and technology.) However the term generative is usually used for art in which these systems play a major role in the work, with significant autonomy from the artist's urges. It thus invokes issues of distributed and non-human creativity.
Computing media nevertheless revolutionize generative art. A great deal of early computer art is generative by necessity, since the machines were expensive and difficult to use.
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Various. Ten Questions Concerning Generative Art
Whitelaw, M. System Stories and Model Worlds: A Critical Approach to Generative Art.
Boden, M., Edmonds, E. What is Generative Art?
Recall that art & design are well-represented within Artificial Life research. Langton accorded importance to the creative and aesthetic aspects of ALife. Several works (notably Karl Sims') have been accoladed in both scientific and art communities. Furthermore, many scholars have noted the aesthetic nature of evaluation of ALife simulations, for their 'lifelikeness' or 'interestingness'.
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Penny, S. Art & Artificial Life - a Primer
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Driessens, E. and Verstappen, M. Natural Processes and Artificial Procedures.
Dorin, A. Enriching Aesthetics with Artificial Life
Dorin, A. A Survey of Virtual Ecosystems in Generative Electronic Art