Unfortunately, he simply dismisses the first two ways with the claim that they are based too much in “antiquated science”. This is a common enough objection to Aquinas, but is simply false.
Beginning with the First Way, this argument has its core in the observation that potentialities do not actualize themselves. That is, something already actual must first exist in order to produce act from potency (to use the traditional terms). To attempt a more modern way of putting it: a possibility can never automatically be a reality simply because it is possible. Rather something merely possible must be realized by something else.
This seems obvious, and Aquinas goes on to argue that there cannot be an infinite string of things being realized in this way, but that the beginning of the chain must be realized without needing something else to realize it.
That is to say, something has to be an uncreated, necessarily extant being. After all, it is only in the case of a being who’s existence is logically necessary do we lack any need for an outside explanation.
As always with this argument, we need to note the fact that Aquinas is not tracing causes backward in time. Rather, he is tracing them “upwards” from effect to cause without reference to time. Most have had a particular type of causation drilled into us so thoroughly that it is hard to imagine any other type.
It is also important to note that Aquinas is only talking about essentially ordered causal series. That is, those series in which removing any link in the chain will prevent its effect from happening.
So, to offer an analogy: If there were a train moving through space, Aquinas would argue (rather reasonably) that it is not enough to say that the back car of the train is pulled by the one in front of it, and that by the one in front of it, and so on. Even if one were to suggest that the train is infinitely long, this would not explain where the motion of the cars ultimately comes from. To stop the “but what moved that” objection, we need to reference something that can move solely under its own power.
Aquinas himself uses the analogy of a rock being moved by a stick which is, in turn, moved by a hand. It is obvious that were we to remove any part of this chain (the hand, the stick, the arm, or any one car from the train), the rock (or the caboose) would not be moving.
Whatever objections one can make to the science of these examples, the basic point is clear: We need what Aristotle called an “unmoved mover” in order to realize the potentialities of things–thereby giving them the power to realize still further potentialities.
And, when one works out the details to their rational conclusion, one is left with the truth that God exists.
This is the third clarification that needs to be made. Those who have read only Aquinas’ famous summary of the Five Ways often complain that he never explains why the conclusion of these arguments is God (Richard Dawkins is a particularly famous example). While it is true that he doesn’t do this in the summaries, he devotes hundreds of pages to this elsewhere.
But, what of the claim that this is all based on “antiquated science”? Mackie doesn’t explain this, but merely references an outside source (Kenny) without addressing the responses that have been made to it. But he needs to. Aquinas’ argument doesn’t depend on medieval cosmology, but on the nature of causal relations.
In fact, Mackie’s response seems like dismissiveness, rather than a serious objection. It’s not any better than Bertrand Russel’s claim that science (presumably quantum mechantics) has destroyed the notion of causation.
But, to pick up that thread, it is notable that Russel’s response is never given by an actual particle physicist. This is because quantum mechanics does no such thing. Indeterminacy is not a logic-busting response to all causation (and, if it were, would be destructive of quantum mechanics, not logic). It is based on careful observation of causal chains.
Rather it is science fiction and bad science documentaries, not actual scientists, that have taught us to doubt causation. There is (very much) more that could be said, but, at the end of the day, nothing about modern science counters Aquinas’ point.
And I don’t understand what makes Mackie so confident that it does that he doesn’t even bother addressing Aquinas’ argument in a book intended as (and which, for the most part, is) a serious critique of the arguments from God’s existence.