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Introduction to Philosophy

Part III. Thomas Aquinas, "The Argument from Necessity"

Abstract: Thomas' Argument from Necessity is outlined and explained. He argues that since all existent things depend upon other things for their existence, there must exist at least one thing that is a Necessary Being. Some standard objections to that argument are also briefly discussed.

  1. Thomas' Argument from Necessity begins with a number of empirical observations including the premise that contingent objects in the world come into existence and pass away. The argument is an à posteriori argument, and the conclusion is not claimed to follow with certainty.
    1. The Argument from Necessity:
      1. Since objects in the universe come into being and pass away, it is possible for those objects to exist or for those objects not to exist at any given time.
      2. Since objects are countable, the objects in the universe are finite in number.
      3. If, for all existent objects, they do not exist at some time, then, given infinite time, there would be nothing in existence. (Nothing can come from nothing—there is no creation ex nihilo) for individual existent objects.
      4. But, in fact, many objects exist in the universe.
      5. Therefore, a Necessary Being (i.e., a Being of which it is impossible that it should not exist) exists.
    2. The concepts of necessary and contingent are essential concepts in the history of philosophy. Some examples illustrating a few of the difficulties of these concepts are as follows.
      1. One way to think about Thomas' argument is to consider a straight line extending without bound representing time. If one takes a finite number of line segments of a specific length representing the time of existence of objects in the world and places them on that line, then most of the unbounded time-line would be unoccupied. That is, very little of the time would objects exist. Thus, there must be something necessary upon which these existent objects depend since at the present time it would so improbable that objects should exist.
      2. Although the Argument from Necessity is empirical, the concepts of necessary and contingent are logical. The crucial question is in Hume's words, whether matters of fact are being confused with relations of ideas in the argument.
      3. If objects in the world are being constantly generated, does this fact imply that God is necessary for their individual existence? Would it then follow that the sequence of time is a sequence of miracles, since the occurrence of events would no longer be subject to the laws of nature? Is God "necessary" for all existent things individually or for all existent things in toto or for just the first existent thing? With God as necessary existence, how can we rule out Russell's Five Minute World Hypothesis using the principle of simplicity?
  2. Summary list of common objections to Thomas' Argument from Necessity:
    1. The fact that many things exist when, if the argument were correct, the probability of objects existing is self-refuting since being must exist at the same time as these arguments in order to evaluate such arguments.
    2. If God is an existent object in the universe, then by premise (1), it is possible for God not to exist. If God is a different kind of existent thing, then the argument commits the fallacy of petitio principii or the circularity of assuming in the premises what is to be proved.
    3. The premise "If, for all existent objects, they do not exist at some time, then, given infinite time, there would be nothing in existence" commits the fallacy of composition. Simply because the parts of a group are limited, it does not follow that the group as a whole is limited. The properties of whole do not necessarily exhibit the properties of the parts. Simply because all human beings have a finite life-span, it does not follow logically that someday the human race will come to an end— unless, of course, additional assumptions are made. Moreover, in Aristotelian philosophy, the corruption of one being is the generation of another—nothing ceases to exist without the generation of something else.
    4. Necessity is a property of statements not of objects. It doesn't make sense to claim that an existent thing is logically necessary. Existent things just are, that's all. We have no examples of necessary existence; we just have examples of necessary inferences or judgments. There can be no empirical necessities.
      1. As Kant notes, existence is not a real predicate or property; existence is not a characteristic which can be added to the concept of the subject. Thus, the concept of necessary existence is not meaningful. (Q.v., the notes Existence Is Not a Predicate)
      2. The idea of necessary being is unintelligible. As Hume point out, any statement concerning existence can be denied. Hume writes, "The words, therefore "necessary existence," have no meaning, or which is the same thing, none of which is consistent." Whatever we can conceive as existent, we can also conceive as nonexistent.
      3. Nevertheless, Charles Hartshorne claims that the predicate "necessary existence" does add something the concept of God and so is a real predicate or property. E. g., "necessary existence" is distinguished from contingent existence in that necessary existence cannot not exist.
    5. Problem with Creation ex nihilo. Thomas' statement of our premiss (3) that nothing can come from nothing is expressed by him this way: "…that which does not exist begins to exist only through something already existing." This premise implies that the newly existent thing is only a transformation of the already existing thing; otherwise, there would be no way to account for the newly existing thing given the truth of the principle of the conservation of matter and energy. If Aquinas were to deny the principle of the conservation of matter and energy, then he would be tacitly denying the principle of creation ex nihilo for contingent things.
      1. Thomas' does seem to presuppose the principle of the conservation of matter (and tacitly, anything equivalent to matter) in the implicit assumption that the universe is limited.
      2. As reasonable as this assumption appears to be, consider Stephen Hawking's explanation of creation of matter and energy:
        • Where did they [i.e., 1080 particles in the universe] all come from? The answer is that, in quantum theory, particles can be created out of energy in the form of particle/antiparticle pairs. But that just raises the question of where the energy came from. The answer is that the total energy of the universe is exactly zero. The matter in the universe is made out of positive energy. However, the matter is all attracting itself by gravity. Two pieces of matter that are close to each other have less energy than the same two pieces a long way apart, because you have to expend energy to separate them against the gravitational force that is pulling them together. Thus, in a sense, the gravitational field has negative energy. In the case of a universe that is approximately uniform in space, one can show that this negative gravitational energy exactly cancels the positive energy represented by the matter. So the total energy of the universe is zero.
      3. The physicist Heinz Pagels speculates, "Maybe the universe itself sprang into existence out of nothingness—a gigantic vacuum fluctuation which we know today as the big bang. Remarkably, the laws of modern physics allow for this possibility."
    6. Problem of Criterion of Counting. Are space and nature continuous or discrete? Where does one object end and another begin? Is a fist made from a closed hand something or nothing? Where does the fist go when the hand is opened? Where does a lap go when one stands up? In premise (2) there is a serious problem of criterion of counting objects and their parts. How could Thomas handle these and similar examples?
    7. Problem of the Ultimate Consistent of the Universe. Ultimately is nature continuous or discrete? Do we have any good reasons for assuming with Thomas that nature is discrete rather than continuous?
    8. As Hume points out in his Dialogues, nature, the universe itself, or something else could qualify as just as much a "necessary being" as God would. Why would we suppose that there could just be one necessary being in the universe?
Further Reading:
  • “Necessity” Stephan Kürner outlines the various conceptions of necessity in science and philosophy, including both the notions of logical and substantive necessity in the Dictionary of the History of Ideas maintained by the Electronic Text Center at the University of Virginia Library. Emphasis is placed on early Greek philosophy, Christian theology, modern science, rationalism, empiricism, Kant, Hegel, Marx, and twentieth-century views.

  • God and Other Necessary Beings An analysis of concrete and abstract entities which cannot fail to exist by Matthew Davidson in the Stanford Encyclopedia of Philosophy. Emphasis is placed on the seach for grounds for truth of necessary existence.

  • Necessity This discussion of logical, philosophical, and theological necessity including descriptions of metaphysical, physical, and moral necessity is an entry in the Catholic Encyclopedia.
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“Given the theistic view of creation ex nihilo the theist must deny that the universe can be a metaphysically necessarily existent being whose necessity is caused of itself. If the universe or parts of it, do exist necessarily, then it has its necessity from another necessary being, God who has its necessity of itself.” Michael Philip Levine, Pantheism (London: Routledge, 1994), 252-253.

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