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Thomas Aquinas

Thomas Aquinas



since 01.01.06

Introduction to Philosophy

Part I: Thomas Aquinas, "The Argument from Motion"

Abstract: Thomas' argument that since everything that moves is moved by another, there must thereby exist an Unmoved Mover is outlined and explained. Objections to that argument are also briefly examined.

  1. Aquinas' Argument from Motion begins with the empirical observation of motion in the world. Hence, this argument is an à posteriori argument, and the conclusion is not claimed to follow with certainty.
    1. Thus, if Aquinas' argument is correct, the degree of the truth of the conclusion would be comparable to the conclusions of the findings of modern science. It is important to see that since no claim is made as to the certainty of the conclusion but only as to its probability, the argument cannot be criticized on the grounds that the conclusion does not follow with absolute necessity.
    2. Also, note that the concept of motion involves dependency, not necessarily temporal succession. In other words, the argument from motion relies on the concepts of potentiality and actuality rather than that of causal sequence.
    3. The Argument from Motion:
      1. Evident to our senses in motion—the movement from actuality to potentiality. Things are acted on. (Again, note that the argument proceeds from empirical evidence; hence it is an à posteriori or an inductive argument.)
      2. Whatever is moved is moved by something else. Potentiality is only moved by actuality. (An actual oak tree is what produces the potentitality of an acorn.)
      3. Unless there is a First Mover, there can be no motions. To take away the actual is to take away the potential. (Hence, which came first for Aristotle, the chicken or the egg?)
        1. (E.g., the reason a student has the potential to be awake is that he had (actual) toast for breakfast. Toast has the potential to keep the student awake. But (actual) bread has the potential to become toast, and actual grain has the potential to become bread. Actual water, dirt, and air have the potential to become grain. To take away any of these actualities is ultimately to take away the potential for the student to be alert.)
        2. (Aquinas is not rejecting an indefinite or an infinite series as such, the idea is that a lower element depends on a higher element as in a hierarchy, not a temporal series.)
      4. Thus, a First Mover exists.
  2. Summary list of common objections to the Argument from Motion:
    1. There seems to be a contradiction in the argument. Premise (2), "Whatever is moved is moved by another," conflicts with the notion of God in this argument as that of something unmoved, i.e., that of the Unmoved Mover. God, then, is an the exception to the truth of premise (2). Nevertheless, cannot God move or act? If God is pure actuality, then it would seem to follow that God can't do anything, for God is already all that God could be. If, then, God is already all that God can be, there's no potential for God to be able to act or be in any way different from what God is. If God is claimed to have a privileged status and not subject to the firse premise, then the argument becomes viciously circular.
    2. There are inherent problems with the concepts of actuality and potentiality. Why must we presuppose natural processes have a beginning, middle, and end? Is such a scheme a natual one, or is this paradigm imposed by the nature of our thought? Why must there be a beginning to the universe?
    3. By the principle of simplicity, isn't more reasonable to suppose that the universe of objects in motion has always existed than to suppose that we have to account for how things came from nothing? Such a supposition would be in accordance with Newton's first law of motion, the so-called law of inertia:
      • An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an outside force.
    4. Therefore, neither movement nor rest is necessarily the default state of the universe. Hence, the Big Bang theory of the origin of the universe and the Big Rip Theory are initially less plausible than the Steady State Theory, the Loop or Cyclical Theory or the Pulsating Universe theory.
    5. Natural processes might be best explained without recourse to the dependence of one part to others. Can the notion of the independent interdependence of parts of the universe be just as plausible a notion as some sort of sequence of relations whereby we have to account for the sudden existence of the beginning? For example, if Einstein's Theory of Relativity is correct, absolute motion with reference to three-dimensional space would be replaced with the idea that there is no absolute frame of reference since the motion of anything can only be measured by comparing it relatively with the motion of something else—gravity, acceleration, and motion affect the measurment of time and space.
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“The first mover, in [the argument from motion] is not temporally prior to the movers that depend on it. It is above them all and exists simultaneously with them all, somewhat the way that the sun is the cause of the growth of plants that have secondary causes that produce them successively season after season. The first or prime mover is not of the same order as the things it moves, nor does it move thing in the same way as the secondary causes do.” Stephen F. Brown, “Thomas Aquinas,” The Columbia History of Western Philosophy, ed. Richard H. Popkin and Stephen F. Brown (Columbia University Press, 2005) 254.

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