unmoved mover

It has been suggested that this article or section be merged into Primum movens. (Discuss)

Aristotle, marble copy of bronze by Lysippos. Louvre Museum.

The unmoved mover is a philosophical concept described by Aristotle as the first cause that set the universe into motion. As is implicit in the name, the "unmoved mover" is not moved by any prior action. In his book Metaphysics, Aristotle describes the unmoved mover as being perfectly beautiful, indivisible, and contemplating only the perfect contemplation: itself contemplating.

Reasoning

Aristotle's argument for the existence of the unmoved mover is this: ^{[citation needed]}

• There exists movement in the world
• Things that move were set into motion by something else
• If everything that moves was caused to move by something else, there would be an infinite chain of causes. This can't happen.
• Thus, there must have been something that caused the first movement.
• This first cause cannot itself have been moved, or the infinite chain would start over again.
• Thus, there must be an unmoved mover.

Substance and change

Aristotle begins by describing substance, of which he says there are three types: the sensible, which is subdivided into the perishable, which belongs to physics, and the eternal, which belongs to “another science.” He notes that sensible substance is changeable and that there are several types of change, including quality and quantity, generation and destruction, increase and diminution, alteration, and motion. Change occurs when one given state becomes something contrary to it: that is to say, what exists potentially comes to exist actually. Therefore, “a thing [can come to be], incidentally, out of that which is not, [and] also all things come to be out of that which is, but is potentially, and is not actually.” That by which something is changed is the mover, that which is changed is the matter, and that into which it is changed is the form.

Substance is necessarily composed of different elements. The proof for this is that there are things which are different from each other and that all things are composed of elements. Since elements combine to form composite substances, and because these substances differ from each other, there must be different elements: in other words, “b or a cannot be the same as ba.”

The number of movers

Near the end of Metaphysics, Book Λ, Aristotle introduces a surprising question, asking "whether we have to suppose one such [mover] or more than one, and if the latter, how many."^[1] Aristotle concludes that the number of all the movers equals the number of separate movements, and we can determine these by considering the mathematical science most akin to philosophy, i.e., astronomy. Although the mathematicians differ on the number of movements, Aristotle considers that the number of spheres would be 47 or 55. Nonetheless, he concludes his Metaphysics, Book Λ, with a quotation from the Iliad: “The rule of many is not good; one ruler let there be.”^[2][3]

Notes

1. ^ Aristotle, Metaphysics, 1073a14-15.
2. ^ Iliad, ii, 204; quoted in Aristotle, Metaphysics, 1076a5.
3. ^ Harry A. Wolfson, "The Plurality of Immovable Movers in Aristotle and Averroës," Harvard Studies in Classical Philology, 63 (1958): 233-253.

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