Prof. Richard Swinburne
Doctor Honoris Causa of KUL

 

 

My natural theology

 

 

I appreciate very much the honour which you are conferring on me today. The Catholic University of Lublin was a bastion for the defence of politically unpopular Christian views during the hard years of communist rule; and as one who defends Christian views which are in a milder way academically unpopular today, I am very proud to be numbered among your graduates.

While I am very fortunate to have been able in the course of a long life to study and to write about many important philosophical issues, the central focus of my work has been to examine the meaning and justification of the central doctrines of Christianity and to assess whether there are sound arguments from evident general features of the world to the existence of God, that is whether there is a sound natural theology. The paradigm of knowledge for twenty first century humans is physical science, and so I think it unlikely that any arguments from the world to God will seem plausible to our contemporaries unless they use the same inductive criteria as used in the physical sciences, and also in history and detective work, to argue from observable phenomena to a hypothesis which best explains them. So I hope that it may be of interest to those of you who do not know the details of my work if I spend the next fifteen minutes explaining how I have tried to show that theism, the hypothesis that there is a God, does indeed satisfy those criteria.

 

There are two basic kinds of explanatory hypothesis — personal hypotheses and inanimate hypotheses. A personal hypothesis explains some phenomenon in terms of it being caused by a person, acting with certain powers (to bring about effects), certain beliefs (about how to do so), and a certain purpose (to bring about a particular effect, either for its own sake or as a step towards a further effect). I (a person) cause the motion of my hand in virtue of my powers (to move my limbs), my belief (that moving my hand will attract attention) and my purpose (to attract attention). An inanimate explanation, which is the kind used in the physical sciences, explains some phenomenon in terms of it being caused by some initial state of affairs and the operation on that state of laws of nature. The present positions of the planets are explained by their earlier positions and that of the Sun, and the operation on them of Newton's laws. I suggest that a postulated hypothesis (of either kind) is probably true insofar it satisfies three fundamental criteria. First we must have observed many phenomena which it is quite probable would occur and no phenomena which it is quite probable would not occur, if the hypothesis were true. Secondly, it must be much less probable that the phenomena would occur in the normal course of things, that is if the hypothesis were false. Thirdly the hypothesis must be simple, that is, it must postulate the existence and operation of few substances, few kinds of substance, with few simple properties behaving in mathematically simple kinds of way. We can always postulate many new substances with complicated properties to explain anything which we find. But our hypothesis will only be supported by our evidence if it is a simple hypothesis which leads us to expect the various phenomena that form the evidence.

 

I now illustrate these criteria at work in assessing a postulated personal explanation. Suppose that there has been a burglary; money has been stolen from a safe. A detective has discovered these pieces of evidence: John's fingerprints are on the safe, someone reports having seen John near the scene of the burglary at the time it was committed, and there is in John's house an amount of money equivalent to the amount stolen.

 

The detective puts forward as the explanation of the burglary the hypothesis that John robbed the safe. If John did rob the safe, it would be to some modest degree probable that his fingerprints would be found on the safe, that someone would report having seen him near the scene of the crime at the time it was committed, and that money of the amount stolen would be found in his house. But these phenomena are much less to be expected with any modest degree of probability if John did not rob the safe; they therefore constitute positive evidence, evidence favouring the hypothesis.

 

But a hypothesis is only rendered probable by evidence insofar as it is simple. Consider the following hypothesis as an explanation of the detective's positive data: David stole the money; quite unknown to David, George dressed up to look like John at the scene of the burglary; Tony planted John's fingerprints on the safe just for fun; and, unknown to the others, Stephen hid money stolen from another burglary (coincidentally of exactly the same amount) in John's house. If this complicated hypothesis were true, we would expect to find all the positive evidence which I described, while it remains not nearly as probable otherwise that we would find this evidence. But this evidence does not make the complicated hypothesis probable, although it does make the detective's original hypothesis that John robbed the safe probable; and that is because that hypothesis is simple. The original hypothesis postulates only one person (John) doing one thing (robbing the safe) which leads us to expect the various pieces of evidence; while the rival hypothesis which I have just set out postulates many substances (many persons) doing different unconnected things.

 

The same criteria are at work in assessing scientific hypotheses postulating different laws and different initial conditions as explanations of phenomena. To be probable a scientific hypothesis has to make probable the occurrence of many observed phenomena, the occurrence of which would otherwise be very improbable. But for any finite collection of phenomena there will always be an infinite number of different hypotheses which could be constructed and which will make the same phenomena just as probable as a given hypothesis, yet postulate the existence of different entities and make different predictions for the future. For example instead of Newton's law that every material object attracts every other material object with a force proportional to the product of their masses and inversely proportional to the square of their distance apart, there could be a law that such attraction only operates until the galaxies are a certain distance apart (a distance they will attain tomorrow), after which they will repel each other. Without the criterion of simplicity science could only summarize observations — there would be no reason to extrapolate from the observations to Newton's hypothesis rather than any rival hypothesis.

 

Now to apply all this to theism. The phenomena from which we can argue to theism are the most general features of the universe — the facts that all physical objects behave in accord with the same fairly simple physical laws, that these laws are such as — given the Big Bang — will probably lead to the evolution of human bodies somewhere at some time in the universe, and that humans are conscious beings. The hypothesis of theism is a personal explanation which seeks to explain these phenomena by the action of an everlasting person who has unlimited power (is omnipotent), true beliefs about what is good and bad, and totally good purposes. HIs omnipotence entails the two latter properties. For to be truly omnipotent, he will have to know the nature of every action which it is logically possible for him to do. He will therefore know which actions are good and which actions are bad. Being omnipotent, he will not be influenced by any irrational influences, and so will always do the best possible action in any circumstances; if there is no unique best action available to him, he will do some good action. So he will be perfectly good. A perfectly good being will seek to spread goodness. We humans are very good things in virtue of having a kind of goodness which God himself does not have — the ability to choose between good and evil, and so to choose whether to benefit or harm ourselves, each other, and the world, and so to choose by our actions to form our character for good or bad. God, who can only do good, will see it as a great good that there should be other beings who can choose whether or not to do good. But we can only choose which effects to produce if the world is governed by fairly simple and so comprehensible laws, for only thereby can we know the effects of our actions; the laws must be such as to cause or permit the existence of human bodies; and in order to have choices, we must be conscious beings. So these very general phenomena are to be expected with some modest degree of probability if there is a God.

 

But if there is no God, it is immensely improbable that these phenomena will occur. It is enormously improbable that each of the innumerably many chunks of matter-energy of which the universe (or the multiverse - if there is a multiverse) was originally made should just happen by chance to behave in exactly the same way at each other - the way codified in 'laws of nature'; for example that every chunk should attract each other chunk with a force proportional to the product of their masses and inversely proportional to the square of their distance apart. This is immensely improbable, whether the Universe came into existence at the Big Bang or has always existed. And even if such an enormous coincidence occurred by chance, it is immensely improbable that these chunks of matter-energy should be such as together with the boundary conditions of the universe (or of the multiverse - if there is a multiverse) to give rise to human bodies. And even if this too occurred by chance, as far as any plausible scientific laws are concerned, the laws might just as easily have given rise to zombies. Consciousness is totally improbable, unless there is a creator who gave it first to the higher animals and then to us. Theism is a very simple hypothesis. It postulates just one entity, God having zero limits to his power and length of life. Zero is a very simple number — much simpler than 52 or 2¹². Yet all the divine properties follow from his everlasting omnipotence.

 

I conclude that the hypothesis of theism satisfies the three criteria for a good explanatory hypothesis which I stated - it makes it probable that the world will have the general features it does, which would otherwise extraordinarily improbable, and it is very simple. Hence it is probably true. Of course every stage of my argument has been questioned; and I cannot pursue now all the details of the resulting controversies here. But it may be that many of you share my conviction that only a natural theology which uses the criteria used in modern science is likely to convince modern man; and I have tried to show you what such a natural theology looks like.