1. Introduction
In ‘Famine, Affluence, and Morality’, which is a seminal article on one's obligations regarding poverty, Peter Singer outlines two distinct moral principles, which I call the Stronger Principle of Sacrifice and the Weaker Principle of Sacrifice, respectively.Footnote 1
Stronger Principle of Sacrifice. If it is in our power to prevent something bad from happening, without thereby sacrificing anything of comparable moral importance, we ought, morally, to do it.Footnote 2
According to the Stronger Principle of Sacrifice, individuals ought to sacrifice everything except their necessities to alleviate poverty. One of the prevalent objections to the Stronger Principle of Sacrifice is demandingness. The demandingness objection initially attacks act consequentialism. Critics claim that act consequentialism is implausible since it requires unrealistically high sacrifices from individuals, carries the risk of being seriously detrimental to individuals by leading to alienation and the violation of integrity, and rules out the pursuit of self-interest and personal projects.Footnote 3 Subsequently, the Stronger Principle of Sacrifice is also vulnerable to the demandingness objection against act consequentialism. Singer has submitted a general response to the demandingness objection in which it is stated that individuals can still first take care of their interests because some degree of partiality is granted under a moral theory based on impartiality.Footnote 4 Regardless of the success or failure of the demandingness objection, Singer articulates another principle which can bypass the demandingness objection, namely, the Weaker Principle of Sacrifice.
Weaker Principle of Sacrifice. If it is in our power to prevent something very bad from happening, without thereby sacrificing anything else morally significant, we ought, morally, to do it.Footnote 5
The Weaker Principle of Sacrifice has not been studied as much as the Stronger Principle of Sacrifice presumably because Singer embraces the Stronger Principle of Sacrifice.Footnote 6 However, the Weaker Principle of Sacrifice can be attractive to many of those who are concerned about poverty, because it is not as demanding as the Stronger Principle of Sacrifice. For instance, effective altruism, which has been inspired and reinforced by Peter Singer, is often a more accessible and practicable approach to fulfilling our obligations regarding poverty. ‘Unlike utilitarianism,’ says William MacAskill, ‘effective altruism does not claim that one must always sacrifice one's own interests if one can benefit others to a greater extent.’Footnote 7 It should be no coincidence that most of the donation campaigns initiated by effective altruists target 10% of individual income rather than much more, which aligns not with the Stronger Principle of Sacrifice, but with the Weaker Principle of Sacrifice.Footnote 8 The effective altruism community aside, it is presumably easier to find people who are ready to commit to less demanding principles than more demanding principles when it comes to sacrificing one's things to benefit others.
In this article, I focus on the Weaker Principle of Sacrifice. There are several reasons for this. First, much has been discussed around the extent to which we should sacrifice morally significant things, but what is meant by moral significance, and the possible readings of it, is left unnoticed.Footnote 9 Second, moral principles are often objected to on the basis that they are overdemanding, but it is important to show that they can also be objected to on the basis that they are overpermissive, and the Weaker Principle of Sacrifice is one of those principles which can indeed be objected to on this basis. Third, the Weaker Principle of Sacrifice is overshadowed by the Stronger Principle of Sacrifice, although the former is relatively more practicable. Because of the demandingness of the Stronger Principle, the Weaker Principle of Sacrifice can realistically be followed by more people, and thus merits analysis.
I start by disambiguating the Weaker Principle of Sacrifice, which invokes the otherwise undefined notion of moral significance, and show that it is open to different readings, because there are at least four interpretations of moral significance. These different interpretations of moral significance are important because they can radically change how we understand the Weaker Principle of Sacrifice, and how we understand our moral obligations towards poverty. Next, I clarify what lavish pursuits are, and how they may be of moral significance. By focusing on one specific interpretation of moral significance, which links moral significance to gaining or losing a considerable amount of welfare, I introduce the permissiveness objection. The permissiveness objection states that the Weaker Principle of Sacrifice can be overpermissive because it permits us to not sacrifice some morally significant things, namely, deliberately cultivated morally significant lavish pursuits. By exempting them from the domain of sacrifice, the Weaker Principle of Sacrifice also puts a comparatively unjustifiable burden on those who have not deliberately cultivated morally significant lavish pursuits. This leads me to conclude that we have to find another principle to supplement the Weaker Principle of Sacrifice, such as the Permissiveness Principle that I introduce towards the end of this article.Footnote 10
2. How should we interpret moral significance?
The Weaker Principle of Sacrifice says that we must prevent very bad things from happening unless this involves giving up something of moral significance. This immediately raises the question of what counts as morally significant. Singer does not explicitly discuss what is meant by moral significance in the article in which the Weaker Principle of Sacrifice is formulated. There could be varying interpretations of moral significance, four of which are the following:Footnote 11
1. Anything that increases or decreases one's welfare is morally significant, regardless of how small or large the amount of welfare is.
2. Anything that puts one's welfare above or below a critical level is morally significant.
3. Anything that considerably increases or decreases one's welfare is morally significant.
4. Anything whose sacrifice produces a sufficiently small welfare gap between what is to be gained and what is to be lost is morally significant.
The first interpretation demonstrates that we could explain moral significance with respect to the mere existence of utility, regardless of the amount of it. This is a very broad interpretation of moral significance, which practically entails that things which create huge differences in one's welfare (such as getting the dream job), as well as infinitesimal differences (such as touching the water's pleasant texture for a moment), could count as morally significant. Away from the context of the Weaker Principle of Sacrifice, it seems plausible that welfare is morally significant. If, without sacrificing anything (say, by clicking our fingers), we could make a person slightly better off, we at least seem to have some moral reason to do it. This suggests that utility, no matter how slight, is morally significant, for how could it ground a moral reason if it had no moral significance?
One may rightly expect that some utilitarians could be attracted to this interpretation because they think that all that matters springs from changes in welfare. In that respect, infinitesimal changes are always factored in as they are always morally significant – after all, they are changes in one's welfare, and they morally matter. If we think that the Weaker Principle of Sacrifice considers any amount of utility to be morally significant, then it would be very hard to assign a moral obligation to alleviate poverty because virtually any sacrifice could somewhat decrease individuals’ actual or potential welfare. In that respect, taken to its extreme, the Weaker Principle of Sacrifice would hardly demand anything of us, in terms of alleviating poverty. As long as donating money would mean forgoing spending on anything that could produce any utility, we would be permitted not to donate. Having room for justifying almost any spending means that individuals can exclude peculiar things from the domain of sacrifice even though it is implausible to exclude them. For instance, Carl Knight states that:
Many adults have their own consumerist sources of happiness (however short-lived), and these sources also take on moral significance. And once this is accepted, one who endorses [the Weaker Principle of Sacrifice] can simply observe that aiding the global poor will almost always have some morally significant opportunity cost.Footnote 12
To illustrate Knight's point, since smelling perfumes’ alluring scents relieves the tiredness of an enervating day, and since the appreciation of the scents gives an increased pleasure, spending money on dozens of perfumes may be morally significant if one is attracted to perfumes. In that case, the Weaker Principle of Sacrifice would not require the money spent on perfumes to be donated to a charity. Likewise, Otteson notes that:
People will have sharply different views about what level of sacrifice begins to be ‘morally significant,’ and until one can locate a specific, concrete criterion, one would have to live with some people not giving any money to overseas relief agencies because they think that anything – even $1 – is morally significant.Footnote 13
These points show that, if moral significance is tied to any amount of utility, even the moral significance attached to short-lived consumerist choices can excuse an agent from the obligation to alleviate poverty. In that respect, despite the fact that the Weaker Principle of Sacrifice is formulated to provide individuals with a less demanding principle, it would cause another complication, that is, being overpermissive. In other words, if individuals can justify almost any spending that is morally significant according to the Weaker Principle of Sacrifice, then the Weaker Principle becomes futile because it is unable to assign moral obligations in almost all circumstances. Since this interpretation of moral significance is too broad and encourages people to overwhelmingly prioritise their own interests, there is no point in formulating the Weaker Principle of Sacrifice in this way, because doing so renders it practically empty. Hence, the first interpretation of moral significance seems to be implausible.
In the second interpretation, moral significance becomes a threshold concept, one which is sensitive to a certain level of welfare, that is, surpassing a critical level of welfare or being under a critical level of welfare could be of moral significance. In that case, anything that helps one to surpass a critical level of welfare or forces one to be under a critical level of welfare could be morally significant. The second interpretation is compatible with what Singer might have had in mind, but arguably it is not the one that Singer would accept. Singer does not mention any type of critical level and the standard connotation of moral significance for a utilitarian is likely to be associated with the amount of welfare and not with a critical threshold.
In the third interpretation, moral significance could be understood with respect to the amount of welfare gained or lost. Under this interpretation, the moral significance of a thing is correlated to that thing's impact on one's welfare. This interpretation is sharply different from the second interpretation. To illustrate the difference, suppose that, under the second interpretation, anything that pushes our welfare above or below X is morally significant. And suppose that we have a welfare of X−1. We do something and our welfare is now X+1. We gain 2 units of welfare. According to the second interpretation of moral significance, that thing is morally significant. Further suppose that we have a welfare of X−10. We do something, and our welfare increases to X−2. We gain 8 units of welfare, which is considerable. According to the same interpretation of moral significance, this thing is not morally significant. However, according to the third interpretation, it is, because 8 units of welfare is considerable. In this example, assessing the moral significance of things with respect to a critical level does not take into account the importance of the amount of welfare gained or lost, something with which Singer is not likely to agree. The amount of welfare gained or lost would be very important for Singer, and for many utilitarians, which is captured by the third interpretation.
In the fourth interpretation, moral significance is ‘relativised’. If the welfare gap between what is gained and what is lost as a result of a sacrifice is sufficiently small, then that thing is morally significant – yet, if the welfare gap is sufficiently large, then it is not morally significant. Nonetheless, this interpretation has a problem. Consider two cases where we receive a cheap gift. In the first case, selling this gift and buying a gift with the money we gain for a friend would increase the welfare of our friend by +2, and decrease our welfare by −1. In the second case, selling this gift would make us extremely sad (suppose that it is from a loved one who is about to die) and decrease our welfare by −100 over years. But if we had sold it and donated the money to charity, it would greatly benefit some poor person by +300. This interpretation of moral significance would state that in the first case keeping that gift is morally significant whereas it is not morally significant in the second case. This seems odd from the perspective of the agent. This fourth interpretation could only make sense in the cases where we do not lose a considerable amount of welfare while at the same time creating a huge benefit to another person. But, to conclude that, we just need to regard something as morally significant only if it considerably increases or decreases one's welfare. This brings us back to the third interpretation.
Hence, I assume that the moral significance meant by Singer is the third interpretation, or, at least, the third interpretation is the one that many people would presumably understand from the Weaker Principle of Sacrifice.Footnote 14 Consider the following examples reflecting this interpretation of moral significance:
1. Joy receives a very high level of enjoyment from hiking. Not being able to hike would slowly lead Joy to major depression. Therefore, hiking is morally significant for Joy.
2. Ash regards painting as indispensable to the fulfilment of integrity. Painting is Ash's childhood passion. Losing the ability to paint would leave Ash in a hellish situation. Therefore, painting is morally significant for Ash.
3. Devon is aware that having a relationship with their significant other gives them an immense feeling of security because of the exclusivity of their relationship. The deprivation of that immense feeling of security would make Devon extremely sad. Therefore, maintaining their relationship in its current form is morally significant for Devon.
4. River likes their house a lot because of its precious memories. The house gives them a lot of happiness. Not living in the same house for the rest of their life would bring about an unendurable melancholy. Therefore, River's house is morally significant for River.
All of these examples have something in common: if a loss of a thing brings about a loss of a considerable amount of welfare, then it means that the thing at stake is morally significant. These examples are meant to show what moral significance may look like in the real world under the third interpretation.
3. The permissiveness objection
I now introduce the permissiveness objection against the third interpretation. If the permissiveness objection is true, the Weaker Principle of Sacrifice is too weak because it asks too little.
Permissiveness Objection. The Weaker Principle of Sacrifice is overpermissive because it unjustifiably exempts deliberately cultivated morally significant lavish pursuits from the domain of sacrifice, and puts a comparatively unjustifiable burden on those who have not deliberately cultivated morally significant lavish pursuits.
To analyse the permissiveness objection, we first need to understand what lavish pursuits are.
3.1 Lavish pursuits
Some rich individuals have lavish pursuits. Lavish pursuits are not necessities. They are high-end goods, experiences, or actions often pursued for pleasure. They are very expensive. They do not necessarily bring about considerable welfare to rich individuals and are not necessarily morally significant. But some of them may bring considerable welfare to rich individuals, and they might therefore be morally significant. However, if lavish pursuits had been sacrificed to benefit others like the worst-off, then their impact would be immense because the amount of resources reserved for lavish pursuits is tremendous. Regardless of the amount of welfare gains that rich individuals receive from lavish pursuits, pursuing them is unjustifiable and they should be sacrificed for the benefit of others, as there are at least three reasons to think so.
The first reason might be that whenever rich individuals have lavish pursuits, it means that they prioritise extreme self-interest, severely violating the principle of impartiality. The second reason might be that having lavish pursuits is consequentially very bad, because the difference between the welfare gain that lavish pursuits bestow to rich individuals and the welfare loss of the worst-off who could have otherwise benefited from them being sacrificed for good is enormous. The third reason might be that lavish pursuits may evoke a false sense of self-entitlement: rich individuals may think that they have the right to have lavish pursuits, although the resources required by lavish pursuits might have been earned by exploitation, undeserved disadvantages, or harm. In many cases, as the cost of lavish pursuits is very high, it is almost unavoidable that the ability to have lavish pursuits has been gained through some sort of wrongdoing.
Suppose that sacrificing A prevents 1 person, sacrificing B prevents 100 persons, and sacrificing C prevents 10,000 persons from contracting a moderate illness. Further suppose that the welfare gain brought about by not sacrificing A, B, or C is the same considerable amount for the rich individual. However, as we move from A to C, the cost of not sacrificing them also increases, because the number of people who could otherwise benefit from the sacrifice also increases from 1 to 10,000, possibly because the monetary value of C is much greater than the monetary value of A. As long as we agree that there is some point on this scale at which things become lavish pursuits, we would accept the existence of lavish pursuits. Some of the real-life examples of lavish pursuits could include:
1. Renovating home with the latest quite expensive furnishings each year,
2. Collecting costly antiquarian books,
3. Spending money on a private art collection consisting of famous paintings of astronomical value,
4. Buying an extravagant private island for one's own usage.
These are not necessities. Moreover, currently, the amount of resources required by them is so high that spending on them becomes eminently immoral in the face of global misery because of the reasons explained above. Therefore, these can easily be identified as lavish pursuits.
As previously mentioned, some lavish pursuits may bring welfare to rich individuals, and, sometimes, the welfare that they bring is considerable. However, what constitutes well-being is an ongoing debate, and whether lavish pursuits are goods that can benefit one's well-being can also be debated. Roughly, there are three mainstream theories of well-being: hedonism, the desire satisfaction theory, and the objective list theory. Hedonism states that only pleasures and pains matter for one's well-being.Footnote 15 It can easily accept that lavish pursuits can affect one's well-being positively insofar as they give one pleasure. The desire satisfaction theory says that one's well-being is affected by the satisfaction of one's desires.Footnote 16 If lavish pursuits are desired by one, then lavish pursuits, according to the desire satisfaction theory, can be significant for one's well-being. The objective list theory posits that there are objective goods that benefit people no matter what people think about them. Apart from pleasure, a sense of achievement, caring relationships, meaningful knowledge, and autonomy could be among the goods that are commonly put on the objective list.Footnote 17 Lavish pursuits, whatever they are, may not be on the list themselves. However, some lavish pursuits might be instrumental in increasing some goods that are on the objective list. For instance, a lavish pursuit, such as using a private jet, may not be on the objective list itself, but what it brings to rich individuals, such as pleasure or achievement, might be on the list. This, even from the perspective of the objective list theory, may imply that lavish pursuits can be important by providing one with the objective goods (pleasure, achievement, etc.) that contribute to their well-being.
Demonstrably, what may be counted as a lavish pursuit for one person may not be counted as a lavish pursuit for another person due to social conditions. An expensive computer bought by a graphic designer is not a lavish pursuit if the graphic designer needs it to make ends meet in a competitive society. The minimally decent life of the graphic designer can be contingent on that expensive computer because of the ever-increasing aggressiveness of the graphic design industry, which condemns graphic designers who do not have specific computers to low earning prospects and deprivation. Therefore, buying an expensive computer does not amount to pursuing a lavish pursuit in this example.
Note that lavish pursuits are not the same as expensive tastes. People who have expensive tastes ‘need more income simply to achieve the same level of welfare as those with less expensive tastes’.Footnote 18 Lavish pursuits are different in two ways. First, identifying them does not require any interpersonal comparisons – they are simply very expensive goods, experiences, or actions, and can be identified without reference to the choices or lifestyle of an average person. Second, lavish pursuits are always morally wrong because of the vast resources they require, whereas it is debatable whether a person acts immorally in satisfying an expensive taste.
3.2 Unjustifiable broadness and comparatively unjustifiable burden
Now that the concept of lavish pursuits is clear, we can unfold the permissiveness objection. Consider First Couple.
First Couple. Twice a year, the first couple are asked by a travel agency whether they want to go on a luxurious vacation which is specifically designed for them. Luxurious vacations take place at the lovely coastal resort where they met years ago. Since they are quite a rich couple, they can easily afford luxurious vacations. This is the tenth year that they have been offered these luxurious vacations. Each time, they have accepted the offer. The first time they went on one of these luxurious vacations, they were only slightly happier. Nonetheless, over the years, they have deliberately cultivated a habit of going on these luxurious vacations, and the impact of them on their welfare dramatically increased. They have even started to regard going on these luxurious vacations as special, exclusive and incomparable. They have reached the point where not going on these luxurious vacations has become morally significant because the extent of the loss of welfare would be considerable.
Deliberate cultivation is a process whereby we accumulate certain patterns, habits, and behaviour by repeating our actions. In this case, the first couple have repeatedly chosen going on luxurious vacations, and, thus, they have deliberately cultivated these luxurious vacations that are clearly lavish pursuits. However, the Weaker Principle of Sacrifice does not assign a moral obligation to prevent something very bad like poverty befalling the first couple with the resources reserved for their lavish pursuit. The reason is simple: these lavish pursuits are of moral significance (they bring about a considerable amount of welfare to the first couple) and the first couple are not required to sacrifice them to benefit others – by deliberately cultivating the habit of going on luxurious vacations, they simply have raised the bar too high.Footnote 19 Although it is true that the Weaker Principle of Sacrifice would condemn the early vacations that they take, through which the cultivation took place, it cannot condemn the vacations they take now because going on these vacations has become morally significant over time. But this is odd – just because someone has deliberately cultivated a morally significant lavish pursuit, they are no longer bound by the Weaker Principle of Sacrifice. This is why the Weaker Principle of Sacrifice is overpermissive.Footnote 20
Clearly, the overpermissiveness of the Weaker Principle of Sacrifice is unjustifiable and weakens the stringency of the moral obligation to alleviate poverty. The broadness of the Weaker Principle of Sacrifice evokes what Henry Shue calls ‘yuppie ethics’.Footnote 21 Yuppie ethics includes the claim that individuals have a right to satisfy their desire to have extravagant and superfluous experiences such as having ‘gourmet dinners – as part of the “good life” – which is taken to override even the right of helpless children to adequate nutrition’.Footnote 22 As nicely explained by Iason Gabriel, yuppie ethics ‘holds that morality contains a set of radical permissions or entitlements that provide people with near total insulation against the positive moral claims of others, such that it would not be wrong to wrong to [sic] deny them life-saving resources when one could alternatively acquire high-end goods for oneself’.Footnote 23 Indeed, the permissiveness objection exhibits that the Weaker Principle of Sacrifice has the capacity to accommodate yuppie ethics. What is odd about the Weaker Principle of Sacrifice here is that it does not care how many people we could help. Once we hit the required amount of welfare that would affect us considerably, that thing becomes morally significant, and we are off the hook.
The Weaker Principle of Sacrifice causes another complication, which is linked to its overpermissive nature. The complication is that it brings about comparatively unjustifiable burdens. Consider Second Couple.
Second Couple. Twice a year, the second couple are asked by a travel agency whether they want to go on a luxurious vacation which is specifically designed for them. Luxurious vacations take place at the lovely coastal resort where they met years ago. Since they are quite a rich couple, they can easily afford luxurious vacations. Each time, they have rejected the offer, and they are aware that luxurious vacations could make them infinitesimally happier. Not going on these luxurious vacations does not mean that they are sacrificing something morally significant since not going on them does not affect their welfare considerably. They have always stressed the importance of using their resources more wisely and donated their money, which they could have spent on these luxurious vacations. This is the tenth year that they have been offered these luxurious vacations and this is the tenth year that they have donated their money to poverty charities instead.
Although they have the same ability to alleviate poverty by donating to charities, the Weaker Principle of Sacrifice assigns a moral obligation to the second couple but not to the first couple. Since the first couple would have sacrificed something morally significant if they had not gone on luxurious vacations, the Weaker Principle of Sacrifice does not bind them in the first place. However, the second couple are bound by the Weaker Principle of Sacrifice. This means that the Weaker Principle of Sacrifice appeals to moral significance alone to decrease the burden of individuals to alleviate poverty. It follows that the second couple are comparatively unjustifiably burdened because the first couple who have the same ability to alleviate poverty are exempt from sacrificing their lavish pursuit solely on the basis of their possession of a morally significant lavish pursuit. This is odd – the first couple should not be let off the hook just because they have deliberately cultivated morally significant lavish pursuits.Footnote 24
The permissiveness objection is valid whenever there are deliberately cultivated morally significant lavish pursuits. But it does not mean that the Weaker Principle of Sacrifice is overpermissive in general – it is overpermissive in cases where there are deliberately cultivated morally significant lavish pursuits. In that respect, the obligation that the Weaker Principle of Sacrifice assigns should be deemed weak. That is also why there is a need to add another moral principle to avoid these complications and use it beside the Weaker Principle of Sacrifice. The Principle of Permissiveness may suffice.
Principle of Permissiveness. In a world where there are very bad things, individuals ought not to follow their deliberately cultivated lavish pursuits, even if they are morally significant.
The Principle of Permissiveness does not let the moral value of pursuing lavish pursuits outweigh the moral value of alleviating poverty. As opposed to the Principle of Permissiveness, the Weaker Principle of Sacrifice does that. Therefore, if the Weaker Principle of Sacrifice is to be followed, it has to be constrained by the Principle of Permissiveness.
4. Conclusion
In this article, I have closely engaged with the Weaker Principle of Sacrifice, which has been discussed much less than the Stronger Principle of Sacrifice, as the demandingness objection directed at the latter has taken centre stage and Singer favours it over the Weaker Principle of Sacrifice. Discussing the Weaker Principle of Sacrifice is important because it is much more flexible than the Stronger Principle of Sacrifice – it is formulated in the hope of convincing people who may be disenchanted with the Stronger Principle of Sacrifice, and has the potential to resonate with many people. After all, individuals need a clear moral principle on which they can base their actions, and the Weaker Principle of Sacrifice is an easy-to-accept principle. Yet, as I hope to have shown, it has its own problems. There are three key takeaways here.
First, there could be overpermissive moral principles as opposed to overdemanding moral principles, and therefore a moral principle can be objected to on the basis of permissiveness as opposed to being objected to on the basis of demandingness. Here, the permissiveness objection against the Weaker Principle of Sacrifice entails that not all morally significant things should be left outside the domain of sacrifice, including deliberately cultivated morally significant lavish pursuits, where doing so would also distribute burdens incorrectly. However, on other occasions, the permissiveness objection can attack different elements of principles which are found to be overpermissive, as the term ‘permissiveness’ could be revisited, reinterpreted, and subsequently utilised for many other relevant cases.
Second, unpacking the central but vague concept of moral significance is critical, as different interpretations of moral significance drastically change how we view a moral principle that relies on that concept. In that respect, I have introduced four different interpretations of moral significance to better understand the Weaker Principle of Sacrifice, and the different implications that follow from the different interpretations of it. Any principle that appeals to moral significance requires an in-depth exploration of what moral significance may mean, or how it is assumed.
Third, and finally, formulating new principles to limit overpermissive principles is crucial. I have formulated the Permissiveness Principle to limit the Weaker Principle of Sacrifice. The literature is abundant with principles that limit the demandingness of overdemanding principles, but it is also important to limit the permissiveness of overpermissive principles, which has so far been neglected in the literature.
Acknowledgements
I am grateful to Patrick Tomlin for providing me with extensive and constructive comments. I am also grateful to Felix Pinkert for our discussion sessions. I thank Theron Pummer and Simon Caney for their feedback. I also thank the audiences of the Joint Session of the Aristotelian Society and the Mind Association, the Society for Applied Philosophy Annual Conference, and the Work in Progress Seminar at the University of Warwick.
Competing interests
The author declares none.
