Reasons to Believe that there is a God

By Kirsty McHugh, OUP UK

In his book Was Jesus God? Professor Richard Swinburne, the eminent philosophy of Christian religion scholar, probes the key doctrines about Jesus – that he was God Incarnate, atoned for our sins, and rose from the dead – and argues that each has a strong and defensible logical underpinning. In the excerpt from the book below he examines the philosophical argument for believing in God.

Theism, the claim that there is a God, is an explanatory hypothesis, one which purports to explain why certain observed data (or evidence) are as they are. Many scientific or historical hypotheses are explanatory hypotheses: they purport to explain data which the scientist has observed in his laboratory or the historian has discovered in the course of an archaeological investigation. Such a hypothesis is probably true in so far as it is a simple hypothesis which leads us to expect the data which are otherwise unexpected (that is, make it probable that those data would occur, when otherwise it is not probable that they would occur), and fits in with ‘background evidence’ or ‘prior evidence’. Suppose that there has been a burglary: money has been stolen from a safe. The detective puts forward the hypothesis, to explain the money having been stolen, that John robbed the safe. If John did rob the safe, it would be quite probable that his fingerprints would be on the safe, that someone might report having seen him near the scene of the crime at the time it was committed, and that money of the amount stolen might be found in his house. These are data to be expected with some modest degree of probability if John robbed the safe, and much less to be expected if he did not rob the safe; they therefore constitute positive evidence, evidence favouring the hypothesis. On the other hand, if John robbed the safe, it would be most unexpected (it would be most improbable) that many people would report seeing him in a foreign country at the time of the burglary. Such reports would constitute negative evidence, evidence counting strongly against the hypothesis. I shall call evidence of either kind posterior evidence, the consequences to be expected or not to be expected if the hypothesis were true. In so far as a hypothesis makes it probable that we would find all the data we find, and in so far as it would be improbable that we would find these data if the hypothesis were false, that increases the probability of the hypothesis. The more probable it is that we’d find the data if the hypothesis were true, and the more improbable it is that we’d find the data if the hypothesis were false, the more probable the data make the hypothesis.

But a hypothesis is only rendered probable by data in so far 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 crime; Tony planted John’s fingerprints on the safe just for fun; and, unknown to the others, Stephen hid money stolen from another robbery in John’s garage. If this complicated hypothesis were true, we would expect to find all the positive data which I described, when it is not nearly as probable otherwise that we would find the data. But the data do not make the complicated hypothesis probable, although they do make the hypothesis that John robbed the safe probable; and that is because the latter hypothesis is simple. A hypothesis is simple in so far as it postulates few substances and simply describable properties, few kinds of substances and simply describable properties, including properties of behaving in simple ways. The detective’s original hypothesis postulates only one substance (John) doing one thing (robbing the safe) which leads us to expect the data; while the rival hypothesis which I have just set out postulates many substances (many persons) doing different things.

But as well as the posterior evidence of the kind which I illustrated, there may be background evidence, or prior evidence: evidence which is not a (probable) consequence of the truth or falsity of the hypothesis in question, but comes from an area outside the scope of that hypothesis. We may have evidence about what John has done on other occasions, for example, that he has often robbed safes in the past. This latter evidence would make the hypothesis that John robbed the safe on this occasion much more probable than it would be without this evidence. Conversely, evidence that John has lived a crime-free life in the past would make it much less probable that he robbed the safe on this occasion. A hypothesis fits with such prior evidence in so far as the prior evidence makes probable a theory (e.g. that John is a regular safe-robber), which in turn makes the hypothesis in question more probable than it would otherwise be.

The criteria for assessing the detective’s hypothesis apply generally to assessing hypotheses proposed by scientists or historians. If a scientist’s data are such as he expects to find (that is, are such as it is probable will occur) if his hypothesis is true, that makes the hypothesis more probable than it would be otherwise. If they are such as he expects not to find (that is, are such as it is probable will not occur) if the hypothesis is true, that makes the hypothesis less probable than it would be otherwise. The simpler the hypothesis, the more probable it is; and a very simple hypothesis is a lot more probable than any other hypothesis. And if the hypothesis is concerned only with a narrow field (e.g. the behaviour of a single planet), it has to fit with what we know about the wider physical world (e.g. how other planets behave). For many hypotheses there may be no relevant prior evidence, and the greater the scope of a hypothesis (that is, the more it purports to tell us about the world), the less prior evidence there will be. For a very large-scale theory of physics (such as quantum theory) there will be few physical phenomena apart from those within its scope (which it purports to explain), and so little, if any, prior evidence.

The data (the posterior evidence for theism) to which arguments of natural theology typically appeal include the most general features of the universe: that every particle of matter behaves in exactly the same lawlike way as every other particle (obeys the same ‘laws of nature’, for example, Newton’s law of gravity); that the initial state of the universe (the Big Bang) and the laws of nature are such as to bring about the eventual existence (some 13 billion years later) of human beings; and that these humans are conscious beings (have a mental life of thought, feeling, and choice). In Is There a God? and elsewhere I argue that, in virtue of God’s omnipotence and perfect goodness, it is quite probable that these data would occur if there were a God (because he would bring them about); and very improbable that they would occur if there were no God. The way in which I have spelled out the hypothesis of theism earlier in this chapter has the consequence that theism is a very simple hypothesis. It postulates the existence of one entity (one god, not many gods), with very few very simply describable properties. A person with no limits to his power, knowledge, freedom, and life is the simplest kind of person there could be. Infinite power is power with zero limits. Infinite knowledge is knowledge with zero limits because it involves no limit (except one imposed by logic) to the number of well-justified true beliefs. Perfect freedom means that the person’s choices are unlimited by irrational desires. Eternity means no temporal limit to life. And God being ontologically necessary, meaning that there are no others on whom he depends, obviously fits well with his other properties. It is also simpler to suppose that God has these properties essentially, for that makes God a more unified being; it means that the divine properties not merely do not, but could not, come apart. And it is simpler to suppose that God is what he is solely in virtue of his essential properties; that is, he has no underlying ‘thisness’—for that is a more economical supposition. It means that it is not an extra truth about how things are that this God rather than that God is in charge of the universe. If God does not have thisness, any God in charge of the universe would be the same God as any God in charge of the universe. God being what he is in virtue of the essential properties which I have listed makes God not quite a person in the sense in which we are ‘persons’.

Theism is such a wide-ranging hypothesis (it purports to explain all the most general features of the universe) that there is no prior evidence; all the evidence (whether positive or negative) is within its scope—posterior evidence. So if I am right that theism is a very simple hypothesis, which makes it quite probable that there would be a universe with the most general features which I have described when this would be very improbable otherwise, there is a good argument from this posterior evidence to the probable existence of God. In arguing in this way, I have sought to articulate a rigorous argument of a kind which many philosophers, Christians, Jews, Muslims, and others have been giving for the past two or three thousand years.