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Ficino (commenter here at ATP with a great interest in Thomas Aquinas) has kindly produced a critique of Aquinas’ Fifth Way, as famously exhibited in Summa Theologiae. This will be split into several parts. This is the second part, the first part (on the preliminaries) can be found here. Today, will look at the argument and at the first fallacy it commits.

2) Here is Aquinas’ Fifth Way (translation mine):

“The Fifth Way is taken from the governance of things. For we see that some things that lack cognition, namely, natural bodies, operate for the sake of an end: which is apparent from the fact that they operate always or very frequently in the same way so as to attain that which is best. From this it is clear that they arrive at the end, not by coincidence, but from natural inclination (lit: “intention”). Those things, however, that do not have cognition do not tend toward an end unless directed by something cognizant and intelligent, as an arrow by an archer. Therefore there is something intelligent, by which all natural things are ordered toward an end: and this we call God.” ST 1a 2.3 c.

I understand the core of the argument, stripped-down, to be the following. I have not standardized it rigorously because Aquinas does not restrict himself to unitary terms throughout (e.g. he slides from “natural bodies” to “natural things,” on which see 4.b.iv below).

  1. There exists an x such that x lacks cognition and x operates for the sake of an end.
  2. For all x, if x lacks cognition, x is a natural body.
  3. For all x, if x is a natural body and x operates for the sake of an end, x operates by intentionality.
  4. For all x, if x operates by intentionality, x is directed by an intelligence. [I don’t think this premise has to retain “if x is a natural body,” since all cognizant things also are directed by intelligence]
  5. Therefore, for all x, if x is a natural thing [sc. non-cognizant], then x is directed by an intelligence.
  6. Therefore, there exists some y, such that, for all x, if x is a natural thing, x is directed by y, and y is intelligent.

I am pulling 5. and 6 out of the same Latin sentence, which is this: Ergo est aliquid intelligens, a quo omnes res naturales ordinantur ad finem. “Therefore there exists something intelligent, by which all natural things are ordered toward an end.”

As written, this argument is rendered invalid by formal fallacies. Fallacy #1 is a fallacy of a Universal Conclusion drawn from a Particular Premise. Aquinas starts with a particular premise: “some things (i.e. agent substances) without cognition operate for an end.” Yet, Aquinas deduces a universal conclusion, “all natural things are ordered toward an end,” with no middle premises to establish this universal. Fallacy #2. From the universal premise, “all x’s that are inanimate and operate from natural inclination are directed by some intelligent y,” it does not follow that there exist such x’s, directed by an intelligent y. Thus, it does not follow that the intelligent y exists. To deduce from a universal premise that a particular entity exists, when its existence is not established by the premises, is known as the Existential Fallacy. It is a fallacy because one is not entitled to assume that the class over which a universal predicate is quantified has members; there can be classes with no members. We can’t deduce from universal propositions about leprechauns that there exist leprechauns. Aquinas is only entitled to deduce that it is possible that there exists at least one intelligent being that guides at least one natural thing toward an end.

3) Trying to Repair the Formal Fallacies of the Fifth Way.

The late Dominican priest and logician, Joseph M. Bochenski, remarked that “the fifth … gives the impression of being written hurriedly … [t]he logical failing here is so gross that it must be assumed that unless Thomas is simply mistaken, he is tacitly using a proof he later develops…” (“The Five Ways,” Poznan Studies in the Philosophy of the Sciences and the Humanities 73 [2000] 61-92 at 84). Bochenski suggested that Aquinas may be assuming one of the arguments for the oneness of God that he will make in ST 1a 11.3 c, namely, his argument “from the unity of the world.” But as Bochenski points out, that argument differs from the Fifth Way, for it proceeds from the interconnection of all natural things in a system, not as the Fifth does from the claim that particular agents in nature are directed to achieve ends. Can we repair the formal fallacies in the Fifth?

Fallacy #1. Either A) make the conclusion a particular proposition, that some natural things are ordered/directed toward an end by something intelligent, or B) lay down a universal major premise, that all natural things operate for the sake of an end. For Aquinas, A) would be a non-starter. He argues consistently that all things in nature operate as directed by God’s providence. Even when one thing is impeded by another, that event itself occurs within God’s universal causality (e.g. ST 1a 103.7 c), and the thing that impedes is itself directed to an end by God. But if some agents in nature operate autonomously from God’s control or design, the Thomistic claims for God’s providence will not stand.

In fact, in other versions of his teleological arguments, Aquinas opts for B). 1) In the early On Truth 2.3, Aquinas argued a universal claim, that “in natural things we find a natural appetite, by which each and every thing tends toward its own end; from this one must posit some intellect above all natural things, which ordered natural things toward their ends and endowed them with their natural inclination or appetite.” 2) Aquinas repeats a universal claim when he interprets Aristotle’s Metaphysics: “… any natural being is disposed by its own nature. Now the nature of each thing is a kind of inclination implanted in it by the first mover, who directs it to its proper end; and from this it is clear that natural beings act for the sake of an end …” (Comm. in XII Meta. 2634C). 3) In his late Commentary on the Gospel of John, Aquinas starts off again with a universal claim, though it is couched as an empirical truth: “For we see the things in nature acting for an end and attaining to ends which are both useful and certain” (Prologue 3).

Let us apply the principle of charity in interpretation and suppose two things. First, let’s allow that Aquinas has in mind in the Fifth his usual universal premise, “all things in nature operate for the sake of an end unless impeded accidentally by other agents operating for their ends.” Second, in line with his insistence that knowledge begins in sensation and that we get knowledge about God from nature, let’s allow that Aquinas is trying to give credence to his major premise by linking it to experience. In the First Way he said, “it is established (constat) from sensation that some things in this world are in motion,” and he moved to a metaphysical claim about all motion. In the Fifth too I think that from seeing some things act for an end, Aquinas means to generalize a metaphysical claim about final causality in all natural things, i.e. substances. Note that I say “metaphysical.” Aquinas does not invoke experience to argue from induction or probability. From experience, he aspires to gain insight of necessary metaphysical truths. Looking at the Fifth’s logical form, suppose we allow Aquinas to universalize “some things that lack cognition” to “all things that lack cognition.” Will the Fifth go through?

We will continue to analyse this in the next part.

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Jonathan MS Pearce

A TIPPLING PHILOSOPHER Jonathan MS Pearce is a philosopher, author, columnist, and public speaker with an interest in writing about almost anything, from skepticism to science, politics, and morality,...