I finally got round recently to reading Nick Spencer's The Evolution of the West: How Christianity Has Shaped Our Values (SPCK 2016), which has just been released in a new expanded American version. I was very glad I did, and would warmly recommend it to anyone interested in learning more (and certainly more than you will typically hear elsewhere) about the many links between our civilisation and its historic faith. Spencer, who is research director of London-based Theos think tank, has a fine way with words, a sharp and independent mind, and an instinct for a pithy sentence which holds within it more truth than you thought could be squeezed in there.

Highlights for me included the chapter on Britain's history as a 'Christian Nation', and a fascinating chapter on Charles Darwin and his relationship to faith and what he thought about the more controversial applications of his theory to social and moral questions.

Without slipping into a partisan reading of history, Spencer ably shows the pivotal role that Christianity has played (mostly for good though sometimes for ill) in the formation of Western ideas, values, institutions and culture. Careful not to claim too much for the faith, but also not to commit the more common modern sin of not crediting it enough, he engagingly sets out the fruits of his many years' research in these areas. The result is an accessible book for a non-specialist audience which, at this critical moment for our society and culture, is a highly worthwhile read for Christian and non-Christian alike.

This said, however, there were a few points in the book where I don't think Spencer got things quite right. So alongside recommending the book (and I really do – please don't let any of these niggles put you off) I want to record here those points where I think something more needed to be said.

1. Christian civilisation did not suddenly discover natural law in the Middle Ages.

Spencer suggests at one point that the idea of a natural law that is binding on kings as well as people and the basis of all just human law was a medieval development. He writes: 'Rather than serve the king or the state in the preservation of the 'natural' social order, the law came to be seen as an instrument of justice intended to serve the whole populace.' But this is clearly a misrepresentation of the place of natural law in pre-medieval and early Christian thought. The natural law and the egalitarian golden rule are at the centre of the ethical teaching of the church from the earliest times (including in the New Testament) and all through the Patristic period (Ambrose being a prominent example) and there was no sudden change in the later Middle Ages. Spencer does a disservice to the early Christian and Patristic tradition to suggest that before the 12th century Christians did not regard the law as an 'instrument of justice intended to serve the whole populace'.

One oddity about this oversight is that in the previous chapter on distinctive features of Western civilisation and also the following chapter on democracy Spencer explains how throughout the early Middle Ages clerics asserted the equal standing of all before God's law and reminded kings that they too were under it. So he is perfectly aware of how Christians of this era understood law and government. Yet still he manages to give the impression that natural law only became part of Christian thought in the twelfth century. Discrepancies like these are presumably a consequence of the book originating as a collection of separate essays, but it is a pity they were not all ironed out in the edit.

A similar historical bungle occurs in the chapter on human rights. Here, Spencer claims that the idea of rights was all but rejected by Christians until the early twentieth century because rights were too closely associated with the French Revolution and anti-authoritarianism. He writes: 'Rights were not only, it seemed, quintessentially modern but associated with an anti-authoritarianism that, predictably, the churches rejected. This changed in the early decades of the twentieth century and in particular from the 1930s.' This is, to be blunt, a bizarre claim. The idea of natural rights, as a formulation of the natural law, was thoroughly mainstream throughout the Christian West from at least the seventeenth century, with the philosophy of John Locke (an Anglican) of particular (though by no means unique or unusual) influence, and the 1688 Bill of Rights a key piece of legislation. John Wesley appealed liberally to natural rights in articulating his opposition to slavery, as did the evangelical abolitionist movement more broadly. Rights – especially the right to life, liberty and property – were standard fare in political discourse throughout the modern period, for Christians as much as anyone else. Any suggestion otherwise is simply historically inaccurate.

2. Dignity is intrinsic to the image of God not external to it.

In the chapters on humanism and human rights Spencer follows Nicholas Wolterstorff in his increasingly influential argument that human dignity (on which by general agreement human rights rest) can only be grounded in the fact that God loves us all equally. We have value, in other words, because we are valued by God, not because God has made us with an inherent value in virtue of what we are, ie made in his image. Spencer follows Wolterstorff in arguing that the 'Kantian' position that human beings have worth because they have the dignity of possessing rational nature is inadequate because it excludes those who no longer have (or have never had) rational capacity (such as the very young, the mentally incapacitated).

This criticism of the Kantian and traditional natural law position is mistaken, however. On the traditional account, human beings have dignity because they bear the image of God (or in Kant's intentionally secularised language, have rational nature). The dignity of humanity is inherent to its nature as bearing the image of God, because the divine image in humanity shares in the dignity of the divine, ie the divine image has inherent dignity.

It is true that this image is typically understood in part (or indeed primarily) in terms of rational nature. But it would be a misunderstanding (and a misunderstanding of Kant's thought in particular) to think that this makes the dignity or value dependent on the degree of rational capacity a person currently possesses. Kant never argued for that claim, and moreover explained why it did not follow – because it is rational nature that possesses dignity, not rational capacity. The wider framework here is the concept of a law-based natural order in which different natural forms or natures exist in accordance with their own particular principles. The principle of humanity is a free and rational nature (this is what distinguishes us from other natural phenomena, and is why we are subject to morality), and it is this rational nature which bears the image of God, and which all human beings possess at all points of their lives regardless of their present state of mental awareness or rational capacity.

Spencer's (and Wolterstorff's) view is philosophically and logically problematic because it fails to recognise that God loves us because we bear his image. Instead it supposes human beings (despite bearing the image of God) in themselves have no dignity or value, but only gain their value from being loved by God, ie their value is not internal to the image they possess but bestowed externally by the extraneous loving action of God. Note that God's love for humanity here cannot be on the basis that humanity bears his image (which would concede the point) and so must be arbitrary. But that would mean God could just as well have loved dust, for instance, and it is just fortunate for us that he loves us. Yet plainly there is nothing arbitrary about the fact that he loves the creatures who bear his image more than he loves dust, for he loves his image because he loves himself, because he is God. The traditional account must therefore be correct: God loves human beings because they bear his image (which gives them dignity, a sharing in the dignity of God) and God loves his image as he loves himself. Human beings thus do not gain their dignity and value from being loved by God but are loved by God and have dignity for the same reason: because they bear his image – an image which includes rational nature.

All this is important because the idea that human beings have dignity because of their rational nature (and their bearing the image of God) is a principle of natural theology which is shared with many other philosophical traditions. The idea that human beings have no intrinsic dignity but derive it externally from being loved by God relies, on the other hand, on a piece of special revelation which is not (necessarily) shared by non-Christians.

It is also important for the sake of logical coherence and philosophical integrity, ie because it is true.

3. Christianity did not play the decisive role in the Scientific Revolution.

Spencer wonders why the Scientific Revolution took place when and where it did, when there had been other smaller scientific revolutions in history (such as in Greece, Rome, Arabia, China) which did not go on to such runaway success. His answer, in common with a number of other recent scholars, is that it was the Christian culture of early modern Europe which provided the key ingredient.

Now I agree that Christianity did (usually) serve as an 'able midwife' (to use Spencer's metaphor) to the Scientific Revolution, providing a highly favourable intellectual environment and often a strong spiritual and motivational spur. Regrettable episodes such as the treatment of Galileo are notable partly because of their rarity.

This does not mean, however, that Christianity was the only philosophy that could possibly have played this role. It provided a strong logical impetus, to be sure, but it was not strictly speaking the only vehicle through which scientific progress could have been made. The most important breakthroughs heralding the Scientific Revolution were developments in mathematics and its application to natural processes (such as Newton's calculus, Cartesian algebra, Boyle's law) and in technology (such as Galileo's telescope), all of which gave a massive boost to the analytical power of science and permitted much better testing of theories.

But the idea that mathematics stands at the pinnacle of natural knowledge and is the key to unlocking the natural world was a central tenet of Greek philosophy (Plato, Pythagoras) and can be seen throughout the Western tradition (the twelfth century philosopher-bishop Robert Grosseteste). So while Christianity certainly provided a strong pair of shoulders on which men of science could stand, it wasn't strictly essential as any similarly reason-based philosophy would eventually (via some gifted individuals and a bit of good fortune) have made similar discoveries – which is why science can be undertaken successfully by people of all kinds of faiths and beliefs, provided they are committed to the primacy of rational analysis and investigation in discovering natural truth.

4. Wealth taxes present many practical and political difficulties – none of which Spencer mentions.

In his chapter on capitalism Spencer reviews Thomas Piketty's Capital in the Twenty-First Century and joins him in endorsing wealth taxes in order to address the currently inexorably increasing levels of global inequality. Although I was somewhat disappointed to find that this chapter was not, as might have been expected, about the role of Christianity in the emergence of capitalism and the opposition to it, I did find myself broadly in agreement with the argument being made for the need to ameliorate excessive inequality (if this were possible) in some way.

A major weakness of the chapter, however, is its lack of any nuanced discussion of the different forms of wealth taxation and the difficulties they encounter in practice. It doesn't, for instance, draw the basic distinction between taxes on the return from capital (rent, dividends, capital gains and so on) and the capital itself. The former are relatively uncontroversial and straightforward to collect while the latter are as a rule much more problematic practically and politically.

The two main examples of wealth taxes (on capital) are 1) an annual wealth or property tax of some kind and 2) inheritance (and more generally gift) tax. These correspond to 1) taxes on the mere possession of capital and 2) taxes on capital when it changes hands. Annual wealth taxes (which are favoured by Piketty and Spencer) have a number of drawbacks which Spencer fails to mention but on account of which they are currently being abolished rather than introduced in most places in the world. The chief problem with them is that the very wealthiest (including the top one per cent, who own around half of the world's wealth) are generally able to avoid them (by clever accounting techniques and offshore holdings) so they largely wind up hitting only those of more modest fortunes as well as penalising stable, easily traceable assets such as land or built assets. Because they miss the very wealthiest they miss most of the wealth and so are largely ineffective in terms of revenue generation and wealth redistribution.

Real property (ie land, buildings) is the main exception to the avoidance problem since it cannot easily be hidden or moved offshore. Property taxes have traditionally targeted built assets ie the improvements to land rather than the land itself. This is mainly because the (market) value of these assets can be ascertained with relative ease and accuracy. However, it is often criticised as disincentivising the development of land and penalising its productive use. Many have suggested, therefore, that a land value tax on the value of the land itself would be a superior form of property tax since it would not penalise development. The main reason such taxes have not been widely implemented in place of traditional property taxes is the acute difficulty in valuing land accurately and fairly in isolation from the developments and improvements upon it, since there is no readily available market value for that quantity.

Traditional property taxes are still widely used. By themselves however they are very limited in what they can achieve in terms of the global wealth redistribution sought by Spencer and Piketty. Attempting to use them in this way, moreover, would be invidious since it would essentially penalise holding capital in the form of real estate rather than other, less traceable, more mobile forms. Countries generally want investors to invest in their real estate and put it to work, and would rather they do this than invest in some of the more lucrative but less socially beneficial destinations that often attract capital.

Annual wealth taxes as a category therefore are of very limited assistance in a global wealth redistribution project.

As regards inheritance or gift tax, the best formof this is probably when it is levied on recipients and when everyone is given a lifetime gift or inheritance allowance, beyond which the taxes apply. The main problem with this idea is, again, that the very wealthiest will always find ways of avoiding it, so it will mainly succeed in hitting those of moderate fortunes and hence will not achieve much in the way of revenue generation or wealth redistribution. It is also politically extremely unpopular, which is a major reason it is not more widely used.

To sum up then, the basic problem with all wealth taxes (on capital) is that their real targets are the top one per cent but, save for real estate (which we don't want to single out to penalise anyway), the top one per cent will always find ways of avoiding them. The taxes will therefore primarily hit those of modest fortunes and so fail to achieve much in the way of revenue or redistribution, while making themselves politically very unpopular in the process. (A global tax-raising authority, as envisaged by Piketty and endorsed by Spencer, would not be a good solution to problems of avoidance as it would be unlikely to work, and even if it did would be horribly undemocratic and corrupt.)

In any case, my real point here is that the chapter needed to include some criticisms of Piketty's ideas such as these and not just present them as the indisputably correct way to proceed.

To reiterate though, these critical observations should not at all be taken to invalidate Spencer's achievement in the book, which in only two hundred pages succeeds admirably in refreshing our memories of what Christianity has ever done for us.

Nick Spencer's The Evolution of the West: How Christianity Has Shaped Our Values is published by SPCK. 

Dr Will Jones is a Birmingham-based writer, a mathematics graduate with a PhD in political philosophy and a diploma in biblical and theological studies. He blogs at www.faith-and-politics.com and is author of Evangelical Social Theology: Past and Present (Grove, 2017). He can be found on Twitter @faithnpolitic