Aristotle argues, in Book 8 of the
Physics and Book 12 of the
Metaphysics, "that there must be an immortal, unchanging being, ultimately responsible for all wholeness and orderliness in the sensible world." In the
Physics (VIII 4–6) Aristotle finds "surprising difficulties" explaining even commonplace change, and in support of his approach of explanation by
four causes, he required "a fair bit of technical machinery". This "machinery" includes
potentiality and actuality,
hylomorphism,
the theory of categories, and "an audacious and intriguing argument, that the bare existence of change requires the postulation of a first cause, an unmoved mover whose necessary existence underpins the ceaseless activity of the world of motion". Aristotle's "first philosophy", or
Metaphysics ("
after the
Physics"), develops his peculiar theology of the prime mover, as : an independent divine eternal unchanging immaterial substance. While the number of spheres in the model itself was subject to change (47 or 55), Aristotle's account of
aether, and of
potentiality and actuality, required an individual unmoved mover for each sphere.
Final cause and efficient cause Despite their apparent function in the celestial model, the unmoved movers were a
final cause,
not an
efficient cause for the movement of the spheres; they were solely a constant inspiration, and even if taken for an efficient cause
precisely due to being a final cause, the nature of the explanation is purely teleological.
Aristotle's theology The unmoved mover, if they were anywhere, were said to fill the outer void beyond the sphere of fixed stars: The unmoved mover is an immaterial substance (separate and individual beings), having neither parts nor magnitude. As such, it would be physically impossible for them to move material objects of any size by pushing, pulling, or collision. Because matter is, for Aristotle, a substratum in which a potential to change can be actualized, any potentiality must be actualized in an eternal being, but it must not be still because continuous activity is essential for all forms of life. This immaterial form of activity must be intellectual and cannot be contingent upon sensory perception if it is to remain uniform; therefore, eternal substance must think only of thinking itself and exist outside the starry sphere, where even the notion of place is undefined for Aristotle. Their influence on lesser beings is purely the result of an "aspiration or desire," and each aetheric celestial sphere emulates one of the unmoved movers, as best it can, by
uniform circular motion. The first heaven, the outmost sphere of fixed stars, is moved by a desire to emulate the prime mover (first cause), about whom, the subordinate movers suffer an accidental dependency. Many of Aristotle's contemporaries complained that oblivious, powerless gods are unsatisfactory. Nonetheless, it was a life which Aristotle enthusiastically endorsed as one most enviable and perfect, the unembellished basis of theology. As the whole of nature depends on the inspiration of the eternal unmoved movers, Aristotle was concerned with establishing the metaphysical necessity of the perpetual motions of the heavens. Through the Sun's seasonal action upon the terrestrial spheres, the cycles of generation and corruption give rise to all
natural motion as efficient cause. something which is aimed at for its own sake. Unlike politics and warfare, it does not involve doing things we'd rather not do, but rather something we do at our leisure. This aim is not strictly human: to achieve it means to live following not mortal thoughts but something immortal and divine within humans. According to Aristotle, contemplation is the only type of happy activity that it would not be ridiculous to imagine the gods having. In Aristotle's psychology and biology, the intellect is the
soul (see also
eudaimonia). According to
Giovanni Reale, the first Unmoved Mover is a living, thinking, and
personal God who "possesses the theoretical knowledge alone or in the highest degree...knows not only Himself, but all things in their causes and first principles."
First cause In Book VIII of his
Physics, Aristotle examines the notions of change or motion, and attempts to show by a challenging argument, that the mere supposition of a 'before' and an 'after', requires a
first principle. He argues that in the beginning, if the cosmos had come to be, its first motion would lack an antecedent state; and, as
Parmenides said, "
nothing comes from nothing". The
cosmological argument, later attributed to Aristotle, thereby concludes that God exists. However, if the cosmos had a beginning, Aristotle argued, it would require an
efficient first cause, a notion that Aristotle took to demonstrate a critical flaw. The purpose of Aristotle's
cosmological argument that at least one eternal unmoved mover must exist is to support everyday change. In Aristotle's estimation, an explanation without the temporal
actuality and potentiality of an infinite locomotive chain is required for an eternal cosmos with neither beginning nor end: an unmoved eternal substance for whom the
Primum Mobile turns diurnally, whereby all terrestrial cycles are driven by day and night, the seasons of the year, the transformation of the elements, and the nature of plants and animals. == Substance and change ==