The fifth argument presented by Edward Feser in his book, Five Proofs, is the rationalist argument. This argument utilizes the principle of sufficient reason, which is usually identified with the rationalist thinker Gottfried Wilhelm Leibniz, the greatest of the modern philosophers.
Before highlighting the argument as it is laid out in Five Proofs, there is a shorter version of the proof found in Feser’s work, Neo-Scholastic Essays, in the chapter titled, New Atheists and the Cosmological Argument.
Here is the argument as presented therein:
II.3 The necessity/contingency approach: A third kind of cosmological argument holds that only a necessary being can be the ultimate cause of the contingent things of our experience. Avicenna defended this sort of argument, as did Aquinas in the Third Way. In modern philosophy, however, it is best known from the versions defended by rationalist metaphysicians like Leibniz and Clarke. One way to understand their approach is as an attempt to show how we can get to the sort of conclusion Aristotelians, Neoplatonists, and Thomists arrived at, but without having to commit to their metaphysical premises. In place of the Aristotelian principle that the actualization of any potential requires a cause and the Neoplatonic principle that anything composite requires a cause – both of which are variations on what is sometimes called ‘the principle of causality’ – the modern rationalist puts the Principle of Sufficient Reason (PSR), according to which there must be a sufficient reason (i.e., an adequate explanation) for why anything exists, any event occurs, or any truth obtains.
There are three key, related differences between the two principles. First, causality is a metaphysical notion, whereas PSR makes reference instead to explanation, which is a logical and epistemological notion. Second, for that reason, whereas the principle of causality is a statement about mind-independent reality as such, PSR is more along the lines of a ‘law of thought,’ a statement about how we have to think about mind-independent reality. Of course, for the rationalist, since the structure of reality can be read off from the structure of thought, PSR purports to tell us something about mind-independent reality as well. But it does so less directly, as it were, than the principle of causality does. Third, whereas proponents of the principle of causality typically hold that nothing can cause itself, proponents of PSR typically hold that something can explain itself. (Of course, some philosophers have held that there can be such a things as a causa sui or self-causing being, but it is not clear that this is or coherently could be anything more than a colorful way of talking about a self-explanatory being.)
David Blumenfeld reconstructs Leibniz’s PSR-based version of the cosmological argument as follows:
- If anything exists, there must be a sufficient reason why it exists.
- But this world exists and it is a series of contingent beings.
- Therefore, there must be a sufficient reason why this series of contingent being exists.
- But nothing contingent – and, in particular, neither the existing series as a whole nor any of its members – can contain a sufficient reason why this series exists.
- A sufficient reason for any existing thing can only be in an existing thing, which is itself either necessary or contingent.
- Therefore, a sufficient reason why this series exists must be in a necessary being that lies outside the world.
- Therefore, there is a necessary being that lies outside the world.
The idea behind step (4) of this argument is that since anything contingent could have failed to exist, there is nothing in its nature that can explain why it exists, so that it requires an explanation outside of itself. This is as true of a collection of contingent things as it is of a given individual contingent thing, since there is no good reason to suppose that a collection of two contingent things is any less contingent than one of them is taken individually, or that three are any less contingent than two, four any less contingent than three, and so on. It might be suggested that this inference commits a fallacy of composition, but on reflection it is hard to see how. Part-to-whole reasoning is, after all, not per se fallacious. It all depends on what property we are attributing to the whole in the basis of the parts. If I infer from the fact that each individual component of a computer weighs less than a pound that the computer as a whole weighs less than a pound, then I commit a fallacy of composition. But if I infer from the fact that every Lego block that has gone into constructing a certain wall is red to the conclusion that the wall itself is red, then I have committed no fallacy. And it seems at the very least highly plausible to say that contingency is in this respect more like redness than it is like weight.
Like Aristotle, Plotinus, and Aquinas, Leibniz argues that this ultimate cause of things that he’s arrived at can on analysis be shown to have various other attributes – which include, Leibniz argues, understanding, will, power, infinity, and unity.
Here is the rationalist argument for the existence of God as presented by Feser in Five Proofs:
- The principle of sufficient reason (PSR) holds that there is an explanation for the existence of anything that does exist and for its having the attributes it has.
- If PSR were not true, then things and events without evident explanation or intelligibility would be extremely common.
- But this is the opposite of what common sense and science alike find to be the case.
- If PSR were not true, then we would be unable to trust our own cognitive faculties.
- But in fact we are able to trust those faculties.
- Furthermore, there is no principled way to deny the truth of PSR while generally accepting that there are genuinely explanations in science and philosophy.
- But there are many genuine explanations to be found in science and philosophy.
- So, PSR is true.
- The explanation of the existence of anything is to be found either in some other thing which causes it, in which case it is contingent, or in its own nature, in which case it is necessary; PSR rules out any purported third alternative on which a thing’s existence is explained by nothing.
- There are contingent things.
- Even if the existence of an individual contingent thing could be explained by reference to some previously existing contingent thing, which in turn could be explained by a previous member, and so on to infinity, that the infinite series as a whole exists at all would remain to be explained.
- To explain this series by reference to some further contingent cause outside the series, and then explain this cause in terms of some yet further contingent thing, and so on to infinity, would merely yield another series whose existence would remain to be explained; and to posit yet another contingent thing outside this second series would merely generate the same problem yet again.
- So, no contingent thing or series of contingent things can explain why there are any contingent things at all.
- But that there are any contingent things at all must have some explanation, given PSR; and the only remaining explanation is in terms of a necessary being as cause.
- Furthermore, that an individual contingent thing persists in existence at any moment requires an explanation; and since it is contingent, that explanation must lie in some simultaneous cause distinct from it.
- If this cause is itself contingent, then even if it has yet another contingent thing as its own simultaneous cause, and that cause yet another contingent thing as its simultaneous cause, and so on to infinity, then once again we have an infinite series of contingent things the existence of which has yet to be explained.
- So, no contingent thing or series of contingent things can explain why any particular contingent thing persists in existence at any moment; and the only remaining explanation is in terms of a necessary being as its simultaneous cause.
- So, there must be at least one necessary being, to explain why any contingent things exist at all and how any particular contingent thing persists in existence at any moment.
- A necessary being would have to be purely actual, absolutely simple or noncomposite, and something which just is subsistent existence itself.
- But there can in principle be only one thing which is purely actual, absolutely simple or noncomposite, and something which just is subsistent existence itself.
- So, there is only one necessary being.
- So, it is this same one necessary being which is the explanation of why any contingent things exist at all and which is the cause of every particular contingent thing’s existing at any moment.
- So, this necessary being is the cause of everything other than itself.
- Something which is purely actual, absolutely simple or non-composite, and something which just is subsistent existence itself must also be immutable, eternal, immaterial, incorporeal, perfect, omnipotent, fully good, intelligent, and omniscient.
- So, there is a necessary being which is one, purely actual, absolutely simple, subsistent existence itself, cause of everything other than itself, immutable, eternal, immaterial, incorporeal, perfect, omnipotent, fully good, intelligent, and omniscient.
- But for there to be such a thing is for God to exist.
- So, God exists.
– Lucas G. Westman