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.
Thomas Aquinas set forth arguments for God’s existence in many places across his vast corpus of writings. Probably the best known today are his arguments from motion (change, really) and from necessary existence. But it was not enough for him to argue that all things must have a universal cause that exists necessarily. Classical theism’s God is also intelligent, and Aquinas needed to establish this. In fact, Aquinas thought the existence of an intelligent governor of the world so evident that, over the span of his writings, he argued to God from nature’s regularities more often than from any other angle. This kind of argument is teleological, an English word coined from the Greek words telos, “end” or “end state,” and logos, here meaning “account.”
Of Aquinas’ teleological arguments, the most famous is the Fifth Way in his Summa Theologiae. There he sets out two primary theses. First, even inanimate things in nature typically act to achieve ends. Second, they can only achieve ends if they are governed or directed by an intelligence. In this article, after 1) some preliminaries, I shall argue that 2) as written, the Fifth Way is invalid; when 3) its quantification fallacies are repaired, 4) the Fifth Way nevertheless is unsound.
1) Preliminaries. (If you’re pressed for time, skip down to 2) in the next article in the series and head back here later.)
First, contrary to what is often thought, the Fifth Way is not a “watchmaker” argument from design. Aquinas is not arguing here that the universe and its components are so complex and work together so intricately that it is only plausible to think a mind designed them. Instead, Aquinas starts from what he thinks are the simplest things in nature, and from their constant operation “on account of an end” he infers that they are directed now by an intelligence. The directing in line with design, not the presence of design, is the key feature. And unlike “intelligent design” arguments, the Fifth Way does not invoke probability or “inference to the best explanation.” Its conclusion is proposed as a necessary metaphysical truth.
Second, some terms in scholastic metaphysics are used in senses that may be unfamiliar.
- “End” (Latin: finis). In discussions of teleology today, we often assume that “end” denotes “purpose” of agents that can make decisions. In Aristotle and Aquinas, natural agents that lack cognition also act toward an “end,” best understood as “final state” or, rather redundantly, “end state.” Aristotle gives the example of teeth, which grow, not by accident or coincidence, but with shapes fit for tearing and/or grinding food (Phys. II.8, 198b24-27). The reason for teeth’s typicality can’t be adequately explained without reference to their function, to perform which is their end. The end of the whole animal is to live the life determined by its form.
- “Intention.” Although the scholastics, as well as modern philosophers, usually use this term for a power of minds, Aquinas also ascribes it to non-cognizant agents, as in “intention of nature.” That’s because by a non-cognizant agent’s “intention” (intentio) he means its orientation or disposition or inclination toward an end. In Aquinas’ analogy of the arrow, the arrow’s direction of flight or aim toward the target is its intentio.
- “Order/ordering.” An “order” (ordo) is a ranked series or relation of distinct members. It has at least one prior and posterior, defined by some principle of origin and/or end point. Something’s motions can be ordered or ranked by how closely they bring the thing to its proper end point.
- “Natural bodies.” At the simplest level, these are the ancient four terrestrial elements, earth, water, air and fire, plus aether, the celestial element; then, bodies composed of these. Bodies of earth were believed to tend by nature toward the center of the universe, the Earth; bodies of fire by nature to tend away from the center upward; celestial bodies of aether to undergo uniform motion. Perhaps today we can say that electrons have an “intention,” natural directedness or inclination, to attract positively charged particles.
- “Natural things,” res naturales. I have not found an instance of this phrase in Aquinas where it does not denote substances. Accidental events in nature do not fall under it. I do not think Aquinas is committed to supplying final causes of coincident phenomena like events of weather or plate tectonics, even if we may be able to trace their efficient causes. Aquinas allows that an eclipse may not have a final cause, because it is a privation, not a substance (Comm. in Metaphysics VIII l. 4 1744C). What he holds is that efficient causes, agents, operate for ends. The agents that cause coincident events operate toward their own ends, but those ends are not the ends of the coincident phenomena, which may lack ends.
Third, Aquinas works from the Aristotelian theory of four causes: efficient, material, formal and final. The formal cause—say, the nature of oak tree—entails the final cause, the existing and operating as an oak tree. Aristotle even says that the formal cause is the final cause (Phys. II.8 199a31). In turn, Aristotelians and Thomists presuppose the final cause when they try to explain the efficient causes of the tree’s operations. What the tree does is directed toward actualizing its end state, its form, and, says the Aristotelian, the tree’s operations can’t be explained without reference to that end state.
Fourth, Aquinas follows Aristotle in holding that final causes or ends in nature are inherent in natural things; the acorn or the sapling, because of the kind of entity it is, has the developed oak tree as its end state. It doesn’t develop toward becoming another kind of tree or organism. Where Aquinas goes beyond Aristotle is to insist that at the universal level, an intelligence, not nature or necessity, guides these operations of natural things. Aristotle thinks “that organisms have final causes, but that they did not come to have them by dint of the designing activities of some intentional agent” (Christopher Shields, “Aristotle,” Stanford Encyclopedia of Philosophy), Aquinas disagrees. He insists that on a universal level, final causality in nature, both as created and in its daily operations, is necessarily the product of a mind.
And so here w3e set the groundwork for the next few articles that will look at the particular claims of Aquinas as pertaining to this famous argument. That said, there is undoubtedly enough in the preliminaries to take issue with, from a point of view of causality.[Ficino earned a Ph.D. in Classics and now works mostly on ancient Greek philosophy and rhetoric].