Unmoved mover

The unmoved mover is a philosophical concept described by Aristotle as the first cause that sets 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. The Unmoved Mover is also referred to as the Prime Mover.


Aristotle's argument for the existence of the unmoved mover progresses as follows:

  1. There exists movement in the world.
  2. Things that move were set into motion by something else.
  3. If everything that moves was caused to move by something else, there would be an infinite chain of causes. This can't happen.
  4. Thus, there must have been something that caused the first movement.
  5. From 3, this first cause cannot itself have been moved.
  6. From 4, 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. 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.”

Modern Criticism

The argument for a Prime Mover is based on the foundation of classical physics — the idea that a body at rest will remain at rest unless acted upon by an outside source. However, while this idea survives in physics since they conveniently and easily describe the movement of objects at the human (that is, not cosmic or atomic) level, it no longer represents the most accurate and truthful representation of the physical universe. Some scientists feel that the development of the laws of thermodynamics in the 19th century and quantum physics in the 20th century have weakened a purely scientific expression of the cosmological argument.

Modern physics has many examples of bodies being moved without any moving body, seriously undermining the first premise of the Prime Mover argument, that every object in motion must be moved by another object in motion. Physicist Michio Kaku directly addresses the cosmological argument in his book Hyperspace, saying it is easily dismissed by the laws of conservation of mass and energy and the laws governing molecular physics. He quotes one of many examples — "gas molecules may bounce against the walls of a container without requiring anything or anyone to get them moving." According to Kaku, these particles could move forever, without beginning or end. So, there is no need for a First Mover to explain the origins of motion.

See also

Cosmological argument

Popular Culture

Atlas Shrugged by Ayn Rand mentions Aristotle's theory as the fourth chapter in Part 1, The Non-Contradiction, with Dagny Taggart and Francisco D'Anconi bearing the title of "Unmovable Movers."


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