Aquinas's First Way through Ontological Dependence — Epoche B2
Aquinas's First Way: Correcting the Temporal Reading, and What the Correction Costs Two ways of hearing the argument Thomas Aquinas's First Way [1] , at Summa Theologiae I [2] , q. 2, a. 3, is the argument he calls the most obvious of his five. It begins from the fact that some things are in motion, argues that whatever is in motion is moved by another, denies that the series can go on without end, and concludes to a first mover that everyone calls God. Popular presentations hear this as a claim about the beginning of the universe: something had to start the sequence of events. Read that way, it is easy to answer. Perhaps the sequence had no beginning. Perhaps cosmology will supply a natural account of the beginning it did have. Perhaps the question "what caused the first cause?" has no non-arbitrary answer. Defenders of Aquinas reply that this is a misreading, and they are right. But the standard defence stops too soon. It establishes that the First Way is not about temporal origins and then treats the argument as vindicated. This essay makes two claims. First, the decisive evidence against the temporal reading is not the stick-and-hand image usually cited but a different article of the Summa altogether. Second, correcting the misreading does not rescue the argument; it moves the weight onto a premise that is harder to defend now than it was in the thirteenth century. What Aquinas means by motion Motus in Aquinas is not travel. It is change of any kind, analysed with a distinction Aquinas takes from Aristotle: potency and act. A thing is in act with respect to some feature when it actually has it, and in potency when it could have it but does not. Cold water is actually cold and potentially hot. Change is the reduction of a potency to act. From this Aquinas derives the premise that whatever is moved is moved by another. Nothing can give itself what it does not have. For water to become hot, something already actually hot must act on it; otherwise the water would have to be, in the same respect and at the same time, both potentially hot and actually hot, which is a contradiction. The premise is therefore presented as metaphysical rather than empirical: it follows from the analysis of change, not from a survey of cases. Two kinds of series Aquinas denies that a series of movers can run on without end. He does not deny this of every series. The distinction is between causes ordered per accidens and causes ordered per se . In a series ordered per accidens, each cause acts and then drops out. A father begets a son; the son can beget in turn long after the father is dead. The causal power is not transmitted through a standing arrangement, and each member exercises it on its own account. In a series ordered per se, the later members have no causal power of their own with respect to the effect; they exercise power only while it is being conferred on them. Aquinas's own image is a hand moving a staff which moves a stone. Take the hand away and the staff does not carry on moving with borrowed momentum; there is nothing left in it to move with. It is worth being honest about the textual position here. The article that states the First Way does not itself set out this distinction. Aquinas sets it out elsewhere, and the passage that matters most is the one considered next. The decisive text At Summa Theologiae I, q. 46, a. 2, Aquinas asks whether it can be demonstrated that the world began to exist. His answer is that it cannot. That the world had a beginning is held by faith; it is not available to philosophical proof. He defends the same position in the short treatise De aeternitate mundi , where he argues that a world created by God and without temporal beginning involves no contradiction — a position that scandalised contemporaries on both sides. This settles the interpretative question. If the First Way concluded to a temporal first event, Aquinas would have proved in question 2 what he denies can be proved in question 46. He was not confused about his own book. Whatever the First Way is, it is not an argument that the sequence of events had a beginning. The same article supplies the other half. In replying to an objection there, Aquinas explains that an infinite regress is impossible among causes ordered per se, but not among causes ordered per accidens, and gives the human generations as his example of the harmless case. So an unending past series of begettings is, for him, philosophically unobjectionable. What he takes to be impossible is a per se series with no first member — because in such a series the intermediate members do nothing on their own account, and an unlimited number of things doing nothing on their own account still amounts to nothing being done. A contrast that clarifies: the kalām argument The temporal argument is a real argument; it is simply somebody else's. In The Kalām Cosmological Argument (1979 [3] ), William Lane Craig revives a line of reasoning from Islamic theology, associated above all with al-Ghazālī, which holds that whatever begins to exist has a cause, that the universe began to exist, and therefore that the universe has a cause. Craig defends the second premise directly, with arguments against the possibility of an actual infinite and with appeals to cosmology. Craig himself is clear that this is not Aquinas's argument, and the contrast is instructive. The kalām argument stands or falls with claims about the past. Aquinas's does not touch them. An objection built from an eternal universe or from a cosmological model without an initial singularity is a live objection to Craig and no objection at all to the First Way. The strongest objection The serious objection is not about regress. It is about the premise that whatever is moved is moved by another, and it was pressed by Anthony Kenny in The Five Ways (1969 [4] ). Aquinas presents that premise as following from the analysis of act and potency, but the cases that make it plausible are cases from Aristotelian