Editing Timaeus (dialogue) (section)

===Nature of the physical world===

[[File:Raffael 067.jpg|thumb|upright=1.02|[[Plato]] is depicted in [[Raphael|Raphael's]] ''[[The School of Athens]]'' fresco in the [[Vatican City|Vatican]], anachronistically carrying a bound copy of ''Timaeus''.]]
[[File:The Three Essences in Plato’s Timaeus.jpg|thumb|The Eternal Essence corresponds to the intelligible world, The Perishable Essence is the realm of sensory experience, where all things are subject to generation and decay. The Intermediate Essence acts as a bridge between these two, harmonizing the cosmos through the World Soul (ψυχὴ τοῦ κόσμου).]]
Timaeus begins with a distinction between the physical world, and the [[eternity|eternal]] world. The physical one is the world which changes and perishes: therefore it is the object of opinion and unreasoned sensation. The eternal one never changes: therefore it is apprehended by reason (28a).

The speeches about the two worlds are conditioned by the different nature of their objects. Indeed, "a description of what is changeless, fixed and clearly intelligible will be changeless and fixed," (29b), while a description of what changes and is likely, will also change and be just likely. "As being is to becoming, so is truth to belief" (29c). Therefore, in a description of the physical world, one "should not look for anything more than a likely story" (29d).

Timaeus suggests that since nothing "becomes or changes" without cause, then the cause of the universe must be a [[demiurge]] or a god, a figure Timaeus refers to as the father and maker of the universe. And since the universe is fair, the demiurge must have looked to the eternal model to make it, and not to the perishable one (29a). Hence, using the eternal and perfect world of "[[Theory of forms|forms]]" or ideals as a template, he set about creating our world, which formerly only existed in a state of disorder.