Edward Feser, Aquinas: A Beginner’s Guide (Oxford: Oneworld, 2009), 51-55.

If you come across a puddle of red liquid near a faucet, you will not suppose that the water in the faucet caused the puddle all by itself. The reason is that water, on its own, does not have within it what is required to generate the effect in question. A leaky faucet by itself might produce a puddle, but not a red one. Hence, you will conclude either that the puddle was caused by something else—a spilled can of soda pop, maybe, or someone bleeding—or that it was caused the water from the faucet in conjunction with something else, such as a “fizzy” tablet dropped in a water puddle or even heavy rust in the water line. In reasoning in this fashion you would be evincing a tacit commitment to the principle of proportionate causality, viz. that a cause cannot give to its effect what it does not have itself, whether formally, eminently, or virtually.

It is nevertheless sometimes suggested that this principle is disproved by evolution, since if simpler life forms give rise to more complex ones then (it is claimed) they must surely be producing in their effects something they did not have to give. But this does not follow. Every species is essentially just a variation on the same basic genetic material that has existed for billions of years from the moment life began. On the Darwinian story, a new variation arises when there is a mutation in the existing genetic structure which produces a trait that happens to be advantageous given circumstances in a creature’s environment. The mutation in turn might be caused by a copying error made during the DNA replication process or by some external factor like radiation or chemical damage. Just as water in conjunction with something else might be sufficient to produce a red puddle even if the water by itself wouldn’t be, so too do the existing genetic material, the mutation, and environmental circumstances together generate a new biological variation even though none of these factors by itself would be sufficient to do so. Thus, evolution no more poses a challenge to the principle of proportionate causality than the puddle example does. Indeed, as Paul Davies points out in The Fifth Miracle, to deny that the information contained in a new kind of life form derives from some combination of preexisting factors—specifically, in part from the organism’s environment if not from its genetic inheritance alone—would contradict the second law of thermodynamics, which tells us that order (and thus information content) tends inevitably to decrease, not increase, within a closed system.

The principle of causality was famously challenged by Hume, who claimed, as we noted earlier, that we can easily conceive of a thing coming into being without any cause at all. What he has in mind is something like imagining the surface of a table which at first has nothing on it, but on which a bowling ball suddenly appears, “out of nowhere” as it were. But there are several problems with the suggestion that this exercise in imagination entails conceiving of something coming into being uncaused. First, it falsely assumes that to imagine something —that is, to form a mental image of it—is the same as to conceive it, in the sense of forming a coherent intellectual idea of it. But imagining something and conceiving it in the intellect are not the same thing. You can form no clear mental image of a triangle that is not equilateral, isosceles, or scalene. But the concept of triangularity that exists in your intellect, which abstracts away from these features of concrete triangles, applies equally to all of them. And so forth. Like many empiricists, Hume conflates the intellect and the imagination, and his argument sounds plausible only if one follows him in committing this error.

Second, as Elizaheth Anscombe pointed out, to imagine something appearing suddenly isn’t even to imagine it (let alone conceive it) coming into existence without a cause. Suppose the situation described really happened to you: a bowling ball suddenly appears on your table. your spontaneous reaction would surely not be to conclude that it came into existence without a cause; rather, you’d ask “Where did that come from?” . . . a question which presupposes that there is a source, a cause, from which the bowling ball sprang. You would also no doubt consider all sorts of bizarre explanations—a magician’s trick, a mad scientist testing a teleportation device, an astronomically improbable quantum fluctuation in the table—before it would even occur to you that there might be no cause. Indeed, this may never occur to you; should even the most bizarre explanation be ruled out, you would probably think “I guess I’ll never know what caused it”—what caused it, not whether it was caused. In any event, there’s nothing about the kind of situation Hume describes that amounts to imagining something coming into existence with no cause, as opposed to coming into existence with an unknown or unusual cause.

But Hume’s argument is more problematic still. Anscombe asks us to consider how we’d go about determining whether the sort of scenario we’ve been describing really is a case of something coming into existence in the first place, as opposed, say, to merely reappearing from somewhere else where it had already existed. And the answer is that the only way we could do so is by making reference to some cause of the thing’s suddenly being here as being a creating cause, specifically, rather than a transporting one. So, the only way we can ultimately make sense of what Hume says we can easily conceive not only hasn’t been conceived by him, it seems likely impossible to conceive.

It is also sometimes suggested that quantum mechanics undermines the principle of causality insofar as it implies that the world is not deterministic. But the Aristotelian does not regard the world as deterministic in any case (determinism being a view associated with the mechanical conception of nature Aristotelians reject), and thus does not hold that every cause must be a deterministic cause. As the analytical Thomist John Haldane has noted, if we can appeal to objective, non-deterministic natural propensities in quantum systems to account for the phenomena they exhibit, this will suffice to provide us with the sort of explanation the Aristotelian claims every contingent thing in the world must have.

So the principle of causality seems secure. And it is worth emphasizing that it is a principle that is in any event presupposed in empirical scientific inquiry—which is in the business of searching for the causes of things—and thus in the very activity held up as the paradigm of rationality by those most inclined to challenge the principle of causality, namely atheists seeking to block “First Cause” arguments for God’s existence.

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Return to Lesson 6: How to Prove God's Existence Through Efficient Causality