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St. Thomas Aquinas and William Paley on Intelligent Design
A Response to Edward Feser
Article. Whether the arguments proving the existence of God from intelligent design given by St. Thomas Aquinas and William Paley agree or disagree?
Objection 1. It seems that the design argument of William Paley is fundamentally opposed to the Fifth Way of St. Thomas Aquinas. “Paley, taking for granted as he does a modern mechanistic view of nature, denies that purpose or teleology is immanent or inherent to the natural order.” The Aristotelian metaphysics of St. Thomas understands final causality as immanent to the nature of every agent as its intrinsic principle of action. But Paley presents final causality as a mechanism imposed onto directionless matter exteriorly through the analogy of human artifice. Therefore, the design arguments of St. Thomas and Paley are incompatible.
Obj 2. Further, “Paley’s argument would justify, at most, belief in a deistic god who gave order to the world at some point in the past but need not be appealed to in order to explain its current operation… Moreover, while Paley and his contemporary successors claim only that the existence of a designer is probable, Aquinas takes the Fifth Way conclusively to establish the truth of its conclusion.” Paley identifies complexity in biological mechanisms as evidence of intelligent design. However, these mechanisms do not necessarily demonstrate the existence of God as Ipsum esse subsistens, as does the Fifth Way of St. Thomas, and instead could indicate a powerful but finite or impersonal intelligent designer, e.g. a deistic watchmaker. Further, natural selection working through the gradual, impersonal coincidences of chance mutations could also explain the presence of design. Therefore, Paley’s argument is inconsistent with the Fifth Way.
Obj 3. In addition, “[w]hile Paley and his successors focus on complex biological structures, Aquinas is not especially interested either in biology or complexity per se; even extremely simple inorganic phenomena suffice in his view to show that a Supreme Intelligence exists.” Paley delineates the mechanisms of biological systems from a scientific standpoint, focusing only on material and efficient causality. St. Thomas, on the other hand, applies final causality metaphysically to all things which act according to their formal natures for ends, without which efficient causality is impossible. Therefore, Paley’s argument is not metaphysical and thus cannot demonstrate the existence of God, unlike St. Thomas’s Fifth Way.
I answer that, The Fifth Way of St. Thomas Aquinas is a necessary metaphysical demonstration of the existence of God from final causality. St. Thomas first observes that natural agents act always or for the most part for the sake of ends perfective of their natures. This ordered necessity indicates that natural agents act by design for their ends. However, using the analogy of archery, he proves that intelligent agents alone can determine their own ends. Therefore, there must be an intelligent designer to provide the final causes of unintelligent agents through their natural inclinations, and this can only be God who alone as Ipsum esse subsistens is his own end and thus requires no higher intelligence.
The design argument of William Paley uses analogies based on human art and sense experience of the natural world to demonstrate the need for an intelligent designer through final causality. Paley systematically compares the mechanisms of biological systems known through the sciences of anatomy and physiology with human machines to show that the parts of living creatures are designed for the sake of ends which they pursue necessarily and consistently. However, unintelligent organisms cannot provide their own ends, nor can any creature design the ends for its parts. Therefore, there must be an intelligent designer to provide the ends pursued by creatures, and this can only be God who alone is self-sufficient:
There cannot be design without a designer; contrivance, without a contriver; order, without choice; arrangement, without any thing capable of arranging; subserviency and relation to a purpose, without that which could intend a purpose; means suitable to an end, and executing their office in accomplishing that end, without the end ever having been contemplated, or the means accommodated to it. Arrangement, disposition of parts, subserviency of means to an end, relation of instruments to a use, imply the presence of intelligence and mind.
The design arguments of St. Thomas and William Paley agree on four fundamental points. First, chance is precluded as an explanation for the purposeful order in natural agents because chance depends upon agents acting by nature for determinate and perfective ends always or for the most part, “for chance itself presupposes causal regularity.” Second, nothing can act without acting for an end, and nothing can act for an end except through intelligence which alone can determine means for the sake of ends as ends. Third, the presence of design in the parts of natural agents beneficial to their natures demonstrates final causality imparted by intelligence. Fourth, all things which pursue ends by the order of their parts, whether intelligent or necessary, must be ordered to their ends by God who alone is self-sufficient as his own end.
Reply to Objection 1. St. Thomas employs and justifies the analogical comparison of human artifacts to Creation as the art of God. Both Paley and St. Thomas use analogies from human artifice to explain examples of teleology in nature which Feser describes as “regularities that point to ends or goals, usually totally unconscious, which are just built into nature and can be known through observation”, not as demonstrations but corroborations for their proofs from final causality. St. Thomas thus writes,
The same may be seen in the movements of clocks and all engines put together by the art of man. Now as artificial things are in comparison to human art, so are all natural things in comparison to the Divine art. And accordingly order is to be seen in things moved by nature, just as in things moved by reason, as is stated in Phys. ii.
In reference to biology, he adds:
Now we observe in the works of nature that either always or more often that happens which is best: thus in plants the leaves are so placed as to protect the fruit; and the parts of an animal are so disposed as to conduce to the animal’s safety.
St. Thomas also teaches that creatures possess finality not by definition but must be designed by the omnipotent intelligence of God, analogical to human artifice. As Fr. Michael Chaberek explains,
Thus, there is nothing in nature that would have an ‘internal’ design, not given from the outside; otherwise, there would be things in nature that do not come from the first intellect, which is impossible... Hence, every design and order in nature is first externally imposed by God, and then it may be passed on by the inherent properties of nature.
Therefore, both Paley and St. Thomas recognize mechanism as “far from being something that could be offered as a substitute for design, is [instead] inseparable from design”, and while the final causes of natural agents are possessed and generated immanently, they originate from God’s specific creative imposition and intelligent direction, without which, as Feser similarly observes, “final causes would immediately disappear”.
Reply to Obj 2. Although focusing primarily on biology, Paley extends his argument further to identify God as the only possible intelligent designer. Paley asserts that anything exhibiting what he calls “contrivance,” meaning an indication of design through which means, especially parts, are the instruments employed by a thing for the sake of determinate ends, cannot ultimately explain its own design, nor can it design itself as this would lead to “the absurdity of self-creation, i.e. of acting without existing.” Further, “even animals and human beings, which are conscious, are comprised in whole or in part of unconscious and unintelligent material components which themselves manifest final causality.” Therefore, since any intelligent designer who is not the same as its intellect could only operate through its intellect as a possessed part, both St. Thomas and Paley recognize God as the necessary source of any conceivable finite intelligence and thus also of the design of all things, animate or inanimate:
The not having that in his nature which requires the exertion of another prior being, (which property is sometimes called self-sufficiency, and sometimes self-comprehension,) appertains to the Deity, as his essential distinction, and removes his nature from that of all things which we see.
Paley also identifies the personhood, goodness, unity, eternity and omnipresence of God through the efficacy of intelligent design and the sustenance of Creation by his power. Further, “[c]hance, properly speaking, does not generate order… because if chance could create order, it would not be chance anymore”, and “chance itself presupposes causal regularity.” Thus, the role of chance in natural selection is insufficient to fully account for intelligent design. Paley’s argument is therefore demonstrative, not probabilistic, of God’s existence.
Reply to Obj 3. The foundation of Paley’s design argument is not in any scientific knowledge but in final causality. Using his knowledge of anatomy, physiology, astronomy and engineering, Paley incorporates the material and efficient causes of natural agents, since these are the two kinds of causality which natural science addresses. However, Paley’s argument is essentially metaphysical by his recognition of final causality and its proof, through intelligent design, for the existence of God. While Paley focuses on “the design that results from finality”, St. Thomas explains finality as the origin of design, identifying form as the end for the sake of which all action is ordered. Beyond biology, Paley also recognizes design as the source of the laws of nature, physics, chemistry, the order of celestial bodies and, like St. Thomas, the harmonious order of diverse natural agents. Therefore, Paley demonstrates the existence of God through the metaphysics of final causality.
Conclusion. Although the design arguments of St. Thomas Aquinas and William Paley differ in background and presentation, they fundamentally agree. Both use observations of the natural world of sense experience, as well as analogies from human artifice, to note that things which lack intelligence behave intelligently due to directedness towards specific ends, and that this proves the existence of God as intelligent designer. Paley, having a wider knowledge of anatomy and modern machinery such as watches, uses more analogies and observations than St. Thomas, who instead focuses on the metaphysical foundation, going beyond Paley to demonstrate that intelligent design toward final ends indicates, in conclusion to the other four ways, that God is Ipsum esse subsistens. However, both fundamentally agree, and one complements the other.
Edward Feser and other critics of Paley could respond to my answers to their objections by emphasizing the contrast in metaphysics and presentation by St. Thomas and Paley. Nevertheless, if Paley’s argument is not confused with those of the modern intelligent design (ID) movement (which, as a scientific theory, employs a “design inference” rather than the philosophical “design argument” of Paley and St. Thomas) or creationism, and if it is treated as complementary rather than synonymous with that of St. Thomas, this opposition can be countered.
 Edward Feser, Aquinas (London: Oneworld, 2009), 115.
 Feser, Aquinas, 111.
 Feser, Aquinas, 112.
 Feser, Aquinas, 113-114.
 Thomas Aquinas, Summa theologiae, I, q. 5, a. 5 (Coyote Canyon Press). Kindle.
 ST, I, q. 2, a. 3.
 William Paley, Natural Theology (Whithorn, UK: Anodos Books, 2019), 170.
 Paley, Natural Theology, 170.
 Paley, Natural Theology, 8.
 ST, I, q. 19, a. 4; Paley, Natural Theology, 29.
 Feser, Aquinas, 113.
 ST, I-II, q. 1, a. 2; Paley, Natural Theology, 8.
 Thomas Aquinas, Summa contra gentiles, III, 3, in Saint Thomas Aquinas Collection (Aeterna Press, 2016). Kindle; Paley, Natural Theology, 9.
 ST, I, q. 22, a. 2, ad 4; Paley, Natural Theology, 170.
 Feser, Aquinas, 116.
 ST, I-II, q. 13, a. 2, ad 3.
 SCG, III, 3.
 ST, I, q. 103, a. 1, ad 3.
 Michael Chaberek, Aquinas and Evolution (Canada: Chartwell Press, 2019), 209.
 D.Q. McInerny, Natural Theology (Elmhurst, PA: Priestly Fraternity of St. Peter, 2005), 153-154.
 Feser, Aquinas, 120.
 Paley, Natural Theology, 9.
 Paley, Natural Theology, 170.
 Feser, Aquinas, 117.
 ST, I, q. 79, a. 1.
 Paley, Natural Theology, 170.
 Cf. Paley, Natural Theology, 169, 187, 185, 183.
 Chaberek, Aquinas, 207-208; cf. Paley, Natural Theology, 135.
 Feser, Aquinas, 113.
 Chaberek, Aquinas, 166.
 McInerny, Natural Theology, 113.
 Paley, Natural Theology, 5, 171.
 Paley, Natural Theology, 173.
 Paley, Natural Theology, 172.
 Paley, Natural Theology, 166, 218.
 SCG, I, 13.
 Paley, Natural Theology, 185.
 Chaberek, Aquinas, 177.