Animal Rights and the Wrongness of Killing

8. Preference Utilitarianism and the Replaceability Thesis

8.1 The Theoretical Replaceability Thesis

In this final section, I want to explore further the notion that one sentient being can be replaced with another where doing so leads to no loss of overall utility. For this purpose, I will focus on Professor Peter Singer's characterization of preference utilitarianism and his replaceability thesis.

The theory of duty that I have been advocating here is unreservedly impersonal and unrestricted. What this means is that the scope of our obligation to maximize mixed utility is not constrained to particular beings, such as those that exist in a specific geographical location, or those that exist now or will exist independently of the moral decision at hand. So, for example, if a moral agent were to extinguish the life of a being and replace it with the life of another with equal utility, with the proviso that the creation of the latter being is not possible except for the extinction of the former and the utilities of no other beings were affected, then no wrong would be committed.

Furthermore, this judgement would hold for lives with any measure of utility and whether the beings were merely conscious or self-conscious. The act would not be wrong just so long as the utilities of the lives of the two beings were the same. Now, if such a replacement of one being with another will lead to an increase in mixed utility, either because the life of the replacement being has a higher utility than the one replaced, or because of an increase in the utilities of the lives of other beings, or both, then this action would be morally obligatory. Let us call this view the 'theoretical replaceability thesis'.

In his Practical Ethics, Singer [1979c: chs 4 and 5] does not find this thesis objectionable when applied to merely conscious animals. However, he rejects its application to self-conscious human and non-human animals. For Singer [1979c: 102], 'rational, self-conscious beings are individuals, leading lives of their own, not mere receptacles for containing a certain quantity of happiness', and so their death cannot be adequately compensated by the creation of a similar being. He feels compelled, therefore, to restrict the application of a utilitarian maximizing principle for self-conscious beings to those beings that already exist or will exist irrespective of the action taken.

In addition to adopting a 'prior existence' view for self-conscious beings, for this same class, he also favours 'preference utilitarianism' over classical or 'mental state utilitarianism'. Conjoining these two views, Singer [1979c: 87, 99, 103] states his maximizing principle for self-conscious beings as an obligation to maximize the satisfaction of rational preferences for only those beings that already exist, prior to the decision that is being taken, or at least will exist independently of that decision.

Book cover: Practical Ethics by Peter Singer

Singer not only wants to hold the 'prior existence' view in order to circumvent the application of the theoretical replaceability thesis to self-conscious beings, but also in order to explain satisfactorily the asymmetry between our moral obligation not to kill and the lack of a moral obligation to bear children. In the previous section, I had already rejected the 'prior existence' view because it contravened a fundamental principle of utilitarianism. Must we accept it now in order to avoid the seemingly unpalatable consequences of the 'theoretical replaceability thesis'? I do not think so. In my Allan [2015: §6–§8], I demonstrated how this asymmetry in our obligations is naturally entailed by the 'mixed' view maximizing principle conjoined with a type of rules in practice utilitarianism. This synthesis, then, can explain what the 'prior existence' view explains without forcing us to accept the unfavourable conclusions of the 'prior existence' view.

Secondly, I can appreciate Singer's aversion to the application of the replaceability thesis to self-conscious beings without being attracted to the 'prior existence' view. Rejecting the replaceability thesis does not logically force us to adopt the 'prior existence' view. This is because the 'prior existence' view entails some moral judgements that are not entailed by the replaceability thesis, given the same ancillary premises. The judgement that a powerful deity is morally blameless for not creating a number of very happy beings ex nihilo is an example.

In the final analysis, though, I am inclined to accept the theoretical replaceability thesis in its application to self-conscious beings. To reject it seems to contravene the utilitarian principle of impartiality. If the satisfaction of a desire to live is valuable, then the principle of impartiality entails that one satisfaction of a desire to live is as valuable as another identical satisfaction of a desire to live. The fact that one satisfied desire exists now while another depends for its existence on an agent's future action is morally irrelevant in deciding what to do. Equal utilities are to count equally.

Consider a scenario in which a mother's son is playing happily in the park. In this example, the mother knows that her son will derive as much enjoyment from playing at home. However, taking him home will involve an action on her part. The question here is whether the son's happiness from playing in the park counts for more than his happiness from playing at home. To argue that the former utility should count for more than the latter because it actually exists simpliciter appears misdirected. Discounting the latter utility because it is only a possibility whose existence is dependent on the mother's action is in breach of the principle of impartiality. The 'prior existence' view is similarly open to this same charge of partiality.[16]

Another problem that arises with the repudiation of the theoretical replaceability thesis is that this rejection looks implausible when we begin to consider replacing one being with many. We may be willing to admit that the replacement of one self-conscious being with another is not adequate compensation for the loss of life of the former. But what if we replace the one self-conscious being with two? If it is felt that this is still insufficient compensation, then what of replacing them with 5 or 10 or 1000 self-conscious beings? It seems plausible to suggest that there is some finite number of lives that would serve as adequate compensation for the loss of one. Singer [1979c: 81, 83] allows that a preference for life 'could sometimes be outweighed by the preferences of others'. However, accepting as he does the 'prior existence' view, these preferences can never be the preferences of replacement beings whose existence depends on the decision of a moral agent.

The surest answer to this question of replaceability, I think, is that provided by the principle of impartiality. Applying this principle means that it is morally permissible for one self-conscious being to be replaced by another of equal utility, all other things being equal. We should not discard the principle of impartiality simply because it leads to one seemingly counterintuitive result. To do this would be akin to rejecting a framework principle in science, such as the principle of the conservation of mass and energy, just because of a single experimental anomaly. In scientific practice, such a rejection would lead to the loss of theoretical justification for countless many experimental procedures, subsidiary theories and laws, with no more adequate replacement available. To abandon the principle of impartiality in utilitarian ethics, likewise, would deprive us of a theoretical justification for race, gender and species equality, with no better theory to replace it.


  1. [16] Sumner [1981: 211–17] provides a good discussion on maximising principles and the principle of impartiality. For a specific criticism of Singer on this point, see also Lockwood [1979: 159ff].

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