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  • Design Arguments and Aquinas's Fifth Way
  • Gaven Kerr

DESIGN ARGUMENTS have traditionally focused on some structured or ordered aspect of the universe and have argued that such order requires the assistance of a supernatural designer. These arguments seek to conclude that order cannot be a product of merely natural processes. The standard instance of this type of argument is William Paley's (in)famous watchmaker argument.1 The mechanical parts of a watch coalesce to allow the watch to function for its designed purpose, that is, telling the time. This purposeful functioning points to a watchmaker who so organizes the parts of the watch as to give them their purpose. The analogy with the created universe is manifest and the argument is applied to infer a cause of the universe. This cause so organizes things that the universe comes about and functions for the purpose for which it, the maker, ordained it.

The salient features of Paley's argument are threefold: (i) mechanistic functioning pointing to (ii) purposeful action which signifies (iii) a designer. These features in turn form part of a venerable tradition in the history of debate on this subject: (i) is a standard presupposition of a modern scientific worldview, (ii) is a presupposition of teleology in nature, and (iii) conceives of the designer as a demiurgic maker who imposes form on the [End Page 447] constituents of the universe.2 Hence standard design arguments are those that come under the aegis of Paley's argument and in particular make use of (i) – (iii) as their guiding principles.

In light of developments in the natural sciences, especially in the theory of evolution, design arguments have somewhat shifted their focus. Now they tend to the view that the probability of the conditions for the possibility of there being anything at all is so slim that there must have been supernatural intervention for it to occur. Nevertheless, such arguments still maintain a focus on the mechanistic functioning of the universe and the inference to a designer as the best explanation thereof. Such recasting of design argumentation remains loyal to some or all of (i) – (iii) in modified form.3

My contention in this article is that Aquinas's fifth way does not fall within the scope of the design argument so construed. Undoubtedly many have thought that it does, since Aquinas's fundamental concern in that argument is to account for the finality operative in unintelligent things, which ultimately rests with God. It is assumed that Aquinas was making the same sort of inference as Paley, namely, that the goal-directed behavior of complex things is a result of the intricate design imposed on them by some supernatural being. Moreover, Aquinas elsewhere employs argumentation similar to that adduced by Paley. If one assumes that the argument of the fifth way is not significantly dissimilar to these other arguments, it is easy to infer that the fifth way is a design argument of roughly the Paleyite variety.4 [End Page 448]

In question 5, article 2 of the disputed questions De Veritate, Aquinas writes:

We see that harmony and usefulness happen in the works of nature either always or for the most part; hence they cannot occur by chance, and thus must proceed through the intention of an end. But that which is without intellect or knowledge is unable to tend directly to an end unless through another's knowledge of an end given to it and directing it to that end. Hence it must be that since natural things are without knowledge, there pre-exists some intellect that ordains natural things to an end; just as an archer gives a certain motion to the arrow so that it tends to a determinate end.5

Similarly, in book 1, chapter 13 of the Summa contra Gentiles, he attributes the following argument to John Damascene and Averroës:

It is impossible for contrary and dissonant things always or almost always to accord [concordare] in one order unless out of some government, by which everything and every single thing are made to tend to a certain end. But in the world we see things of diverse natures coming together [concordare] in one...


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