The Principle of Sufficient Reason and a Rationalist Proof of God's Existence

At Starbucks in Istanbul

Stephen Hawking, in his final book (published post mortem), agrees that our universe began to exist (hence, it is not eternal), but that it could have just popped into existence out of nothing. (See here.) 

William Lane Craig, in his defense of the Kalam Cosmological Argument for God's existence, finds the idea that anything could pop into existence uncaused out of nothing absurd. (See here.) 

In presenting the Kalam argument to my philosophy of religion students I utilize the Principle of Sufficient Reason (PSR). 

1. Whatever begins to exist has a cause.
2. The universe began to exist.
3. Therefore, the universe has a cause.

Once we agree that the universe has a cause, and did not pop into existence out of nothing, we reason that whatever caused the universe to begin to exist must be sufficient to explain how the universe began to exist. That is, by the Principle of Sufficient Reason, we can infer an adequate cause of the universe. 

What about the PSR? Are we rational in accepting it? Edward Feser, in Five Proofs of the Existence of God, beautifully argues for the PSR. 

The PSR states that “there is a sufficient reason or adequate necessary objective explanation for the being of whatever is and for all attributes of any being.” (Feser, p. 148) PSR entails that everything has a sufficient reason. 

This does not mean that everything has a cause. Not all reasons are causes. Something which does not have a cause would need to have its sufficient reason in itself (such as, e.g., God). But if something does not have its sufficient reason in itself, then it exists contingently, and has a cause outside itself. Such as the universe.

Feser asks, why should we believe the PSR?

"Considered as an inductive generalization, PSR is as well supported as any other. For one thing (and as noted already) we do in fact tend to find explanations when we look for them, and even when we don’t, we tend to have reason to think there is an explanation but just one to which, for whatever reason (e.g., missing evidence), we don’t have access. 

For another thing, the world simply doesn’t behave the way we would expect it to if PSR were false. Events without any evident explanation would surely be occurring constantly, and the world would simply not have the intelligibility that makes science and everyday common sense as successful as they are. That the world is as orderly and intelligible as it is would be a miracle if PSR were not true." (Ib., pp. 148-149)

The PSR is far more certain than an empirical hypothesis can be. It is more obviously true than anything that can be said against it. “Though it cannot be directly demonstrated, it can be indirectly demonstrated by the indirect method of proof known as reductio ad absurdum.” (Ib., p. 149, quoting Reginald Garrigou-Lagrange)

To doubt PSR is to claim there is no sufficient reason to affirm PSR. But this is to assume PSR. Feser explains:

"Hence, to doubt or deny PSR undercuts any grounds we could have for doubting or denying PSR. The rejection of PSR is therefore self-undermining. Even the critic of PSR willing to embrace perceptual skepticism and retreat into a redoubt of a priori knowledge will find no shelter there. To reject PSR is to undermine the possibility of any rational inquiry." (Ib., p. 150)

Feser is far more thorough than what I have presented. He handles all objections to PSR and respond to them.

Part of the appeal of PSR is that it seems counter-intuitive to believe that some things exist without explanation. 

The Rationalist Proof of God's Existence looks like this (Go slowly, see Feser's book for explanatory detail, take a deep breath!).

1. 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. 
2. If PSR were not true, then things and events without evident explanation or intelligibility would be extremely common. 
3. But this is the opposite of what common sense and science alike find to be the case. 
4. If PSR were not true, then we would be unable to trust our own cognitive faculties. 
5. But in fact we are able to trust those faculties.
6. Furthermore, there is no principled way to deny the truth of PSR while generally accepting that there are genuine explanations in science and philosophy. 
7. But there are many genuine explanations to be found in science and philosophy. 
8. So, PSR is true. 
9. 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. 
10. There are contingent things. 
11. 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. 
12. 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. 
13. So, no contingent thing or series of contingent things can explain why there are any contingent things at all. 
14. 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. 
15. 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. 
16. 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. 
17. 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. 18. 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. 1
9. A necessary being would have to be purely actual, absolutely simple or noncomposite, and something which just is subsistent existence itself. 
20. 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.
 21. So, there is only one necessary being. 
22. 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. 
23. So, this necessary being is the cause of everything other than itself. 
24. 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. 
25. 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. 
26. But for there to be such a thing is for God to exist. 
27. So, God exists.

(Ib., 161-163)