Summary: Lewis attempts to show that miracles occur and that the Christian God is behind them. However, he neglects to discuss thoroughly the most crucial arguments to establish this, making several incorrect assumptions about opposing beliefs. He relies heavily on assertions followed by inventive analogies which explain his position rather than show its veracity.

In chapter 1, Lewis begins by stating that "the question whether miracles occur can never be answered by experience". This seems a strange thing to say when a good number of religious people claim that a personal miraculous experience is what has convinced them of their god or gods. Furthermore, if miracles do occur and an omnipotent deity who causes them does exist, then it would be possible - at least in theory - for this being to convince everyone in a most spectacular way and beyond a shadow of a doubt that they do exist. On the other hand, if genuine miracles did not occur, we would expect that no evidence would provide support for miraculous events.

As his primary example of something he deems to be miraculous, Lewis gives "Reason", by which he seems to mean human thought processes. He asserts that this is independent of Nature and an influence of God. The difficulty Lewis seems to have with natural brains is mainly founded on the idea of "non-rational causes". As he writes on page 46:

"...its own thoughts, on this supposition, would be the product of non-rational causes and therefore, by the rule which we use daily, they would have no validity".

He rephrases and repeats this idea many times, but at no point explains the distinction he makes between rational and non-rational, nor why he believes that something non-rational could ever give rise to something rational. This is known as emergent behaviour - a thing being greater than the sum of its parts. A similar idea is often expressed elsewhere as "disorder never gives rise to order", which is most often the case. However, there are simple contrary examples, such as the formation of snowflakes or pebbles being sorted by size on a beach.

Lewis' choice of the human mind is perhaps because of all things in the world it is one of the most poorly understood, and was even more so at the time the book was written. We can only guess as to what is meant by rational, but he does believe it is uniquely human (p188). If by "rational" he means "able to make true evaluations about the world", then this is not a uniquely human trait, and nor is being self-aware. Higher primates are able to recognise themselves in mirrors and are aware of their place within a social group, which demonstrates a certain level of self-awareness. The ability to form true beliefs about the world and to act according to those beliefs is inherent in the behaviour of even simple animals. Human mental abilities appear to be a more highly evolved version of this, not something distinctly different. There is no reason why thoughts or artificial inferences which are "caused" could not be correct, useful and reliable. It is difficult to see from the examples he gives what is so unique and so miraculous about human Reason.

At the start of Chapter 10, Lewis writes, "I have argued that there is no security against Miracles to be found by the study of Nature". This is correct, but hardly worthy of 9 chapters to show it. All it says is that science cannot disprove the existence of miracles, which is quite true. They are, by definition, outside of nature and unfalsifiable. We could take every miracle claim ever made and, in theory at least, refute it by showing a simpler and more consistent explanation was to blame, but the miracle-believer could always claim that miracles can occur, but we just haven't witnessed one. That the existence of miracles cannot be disproved, however, should give us no confidence that they do exist. There are a huge number of claims about the existence of beings, supernatural events, or occurrences outside of time or before time that cannot be disproved. The size of this number is limited only by our collective imagination.

As a prelude to establishing the Christian God as the cause of all miracles, Lewis brushes aside all other belief systems with all the cordiality of the British Empire arriving in the Caribbean:

"All the essentials of Hinduism would, I think, remain unimpaired if you subtracted the miraculous, and the same is almost true of Mohammedanism."

Either he has not read much about other religions, or he is hoping that his readers haven't. Both involve miraculous gods who exist outside of nature. Although few religions use the term "miracle" as often as Christianity, they are nonetheless equally worthy of discussion and equally likely to explain aspects of the world or human Reason. He later casts down pantheism, not with any logical arguments, but by reminding us that it is very old and only occasionally fashionable.

In chapter 12 Lewis is in fine form, displaying his usual brand of "proof by analogy". The problem is the question of why an omnipotent creator would create something which would then need changing by way of a miracle. Lewis uses the analogy of a skilled craftsman who knows the general rules for carrying out their job in efficient fashion, but who may occasionally break those rules. He claims that God breaks the rules of Nature through miracles for reasons that we, who are unskilled in the ways of the universe, cannot understand.

This analogy may explain his position very well - he seems to be saying, "God moves in mysterious ways" - but it is lacking in an important respect. A skilled carpenter or musician may learn and know the rules of their skill, including the very rarely-used rules which break them, but God actually makes the rules. There should be no need for him to break any rules, as if he was the omnipotent creator of the universe, he'd have absolute control over the rules and all the starting conditions. If an omnipotent being has a desire, we might expect that desire to come to fruition, but if the being is also perfect, we wouldn't expect that desire to change.

In chapter 12, Lewis discusses David Hume's Essay on Miracles and comes - again - to the correct conclusion that miracles cannot be disproven (p.165). Bizarrely, he then goes on in an attempt to invent some different kind of probability. He tries to cast doubts on our reasoning and building of rules by experience, saying that this is irrational. This is completely untrue. Such rules based on experience form the very basis of how we and many creatures go about our daily lives and are not only rational, but the only way to learn from experience.

"The whole mass of seemingly irregular experience could never have been turned into scientific knowledge at all unless from the very start we had brought to it a faith in uniformity which almost no number of disappointments can shake.
This faith - the preference - is it a thing we can trust? Or is it only the way our minds happen to work?"

That we try to fit irregularities into new rules is a natural extension to this and not to do so would be to give up all knowledge and basis for learning. When we have a limited understanding of the world, we should expect to be surprised from time to time. Trying to find new rules and reasons to account for these surprises is the reason why we don't still think that lightning strikes mean that Thor is angry or that the crops failed because we didn't sacrifice enough.

To those who do not examine his arguments closely, Lewis' ideas will probably feel intuitively right or intuitively flawed depending on the reader's beliefs. Only on closer inspection do the gaping logical holes appear. Throughout the book Lewis acheives little more than making unwarranted assumptions - "rationality cannot come from irrationality" - stating the obvious - "the possibility of miracles cannot be disproven" - and several unconvincing arguments from analogy. The book is, however, quite readable to the lay person. It is worth reading even for those who disagree with his central point, if only to learn why they disagree.