Secretum secretorum - De Mirabilibus Mundi - Terrestrial
Background for Ars Magica sagas

The Physics of the Sublunar Region
Change and Motion

It is frequent to have the impression of Aristotle's cosmos as being static. It is easy to see where this comes from, in the Aristotelian sublunar realm, natural motion ceases when the moving object reaches its natural place, and violent motion comes to an end when the external force no longer acts. If we put everything in its rightful place and get rid of external movers, Aristotle's world will screech to a halt. However, this impression comes from restricting our attention to one kind of change -- change of place or "local motion." Look beneath the surface, not at the location of an object, but at the nature of the object, and the true dynamism of the Aristotelian cosmos becomes apparent. For Aristotle, natural things are always in a state of flux; it is part of their essential nature to be in transition from potentiality to actuality. This is no doubt most obvious in the biological realm, where growth and development are inescapable, but Aristotle's biological studies powerfully shaped his entire philosophy of nature. His definition of nature, as the inner source of change found in all natural bodies, may well have had biological origins, but it was applicable to both the organic and the inorganic realms. The central object of study in Aristotle's natural philosophy, the, was change in all of its forms, and manifestations. Aristotle stated bluntly in his Physics (book 3) that if we are ignorant of change, we are ignorant of nature. If the gross objects that fill Aristotelian cosmos seem to prefer rest over motion, beneath the surface they are seething with change.

Aristotle and his medieval followers identified four kinds of change:

  1. generation and corruption,
  2. alteration,
  3. augmentation and diminution, and
  4. local motion.
Generation and corruption occur when individual things (that is, substances) come into existence and go out of existence. Alteration is change of quality, as when the cold object becomes warm. Augmentation and diminution refer to quantitative change -- that is, change of size, as in rarefaction and condensation. And local motion is change of place the kind of change that seventeenth-century scientists elevated to a place of centrality that it did not have within Aristotelian physics.

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Last modified: Sun Dec 27, 1998 / Jeremiah Genest