Since writing my article on the difficulties of simulating reality (“Shattered Reality”, Game Developer Magazine, August 2006), I learned there is actually a terminology I could have used.

Teleological Modeling is the process of modeling something using real physical rules.

Ontogenetic Modeling is the process of modeling something based on its appearance.

(From Intel: Procedural 3D Content Generation)

To understand the difference between the teleological and ontogenetic approaches, imagine the modeling of clouds. The teleological approach would model the properties of water, its evaporation, temperature of the environment, and so on, to try and produce the desired end result from the bottom up. The ontogenetic approach would be to observe properties of the end result (such as the small wispy bits change more frequently than the larger bits, the shape changes more as the wind picks up, low-lying cloud tends to be darker, and so on). [T]he ontogenetic approach, [...] is more suitable for most real-time applications.

I don’t find the etymology of either word particularly satisfying. “Teleology” less so, as it basically comes from the Greek for “perfect result” and relates to the ultimate “design or purpose” of a thing, and most often crops up in discussion of evolution, philosophy and religion.

“Ontogeny” is the origin and development of an individual from embryo to adult. It’s the details of the process by which DNA creates living things. It describes what happens, rather than why it happens. Since Ontogeny is a description of the results of a process, that’s how it gets this usage in procedural modeling.