A Silent Moral Revolution

In 1975, Australian philosopher Peter Singer published Animal Liberation — a book that would become one of the philosophically most practically impactful texts of the twentieth century, giving decisive impetus to the animal rights movement and motivating legislative changes in several countries. The central thesis is at once simple and radical: the exclusion of non-human animals from full moral consideration has no rational justification — it is a form of prejudice comparable to racism and sexism.

The Concept of Speciesism

The term speciesism was coined by British psychologist Richard Ryder in 1970, in a pamphlet distributed at the University of Oxford. Singer adopted and popularized the concept in Animal Liberation, giving it philosophical rigor.

Speciesism is unjustified discrimination on the basis of species: treating the interests of individuals differently according to the species to which they belong, without any morally relevant difference to justify the distinct treatment. For Singer, just as the racist gives disproportionate weight to the interests of members of their own race, and the sexist to those of their own sex, the speciesist gives disproportionate weight to the interests of members of their own species — human beings.

The Utilitarian Argument: Bentham and the Criterion of Suffering

Singer’s philosophical framework is utilitarian, drawing on Jeremy Bentham and John Stuart Mill. But it is Bentham himself who provides the key formulation. In Introduction to the Principles of Morals and Legislation (1789), Bentham wrote about animals:

“The question is not, Can they reason? nor, Can they talk? but, Can they suffer?”

This sentence — one of the most cited in the history of ethics — shifts the criterion of moral inclusion from rationality or language to the capacity to suffer. For Singer, any being that can experience pleasure and pain has interests — and those interests must be taken into account in moral deliberation, regardless of species.

The principle of equal consideration of interests does not require treating all beings identically, but that equal interests receive equal weight: the suffering of a pig is no less suffering for being the suffering of a pig.

Tom Regan: The Deontological Approach

Tom Regan (1938–2017), in The Case for Animal Rights (1983), starts from different premises than Singer’s, arriving at more radical conclusions. Regan rejects utilitarianism because, in principle, it permits sacrificing individuals if that maximizes overall well-being — which would be unacceptable for humans and animals alike.

Regan’s alternative is deontological: some beings are “subjects-of-a-life” — they have beliefs, desires, perception, memory, an emotional life, preferences, goals, and a psychophysical identity over time. These beings have inherent value, which cannot be reduced to their instrumental value or the sum of their pleasures and pains.

For Regan, normal adult mammals are clearly subjects-of-a-life. As such, they have rights — including the right not to be treated as mere means. The consequence is abolitionist: it is not a matter of reforming animal experimentation, but of abolishing animal experimentation; not of improving conditions for farmed animals, but of abolishing industrial farming.

The Singer-Regan Distinction

The divergence between Singer and Regan is philosophically important:

  • Singer is a consequentialist: what matters is reducing suffering. In principle, if animal experimentation produced sufficiently great benefits and no alternatives existed, it could be justifiable — though Singer argues it rarely is in practice.
  • Regan is a deontologist: certain treatments are wrong regardless of consequences. Subjects-of-a-life have rights that cannot be violated for the sake of the general good.

This distinction connects to the broader debate between utilitarianism and deontology in normative ethics.

Martha Nussbaum: The Capabilities Approach

Martha Nussbaum, in Frontiers of Justice: Disability, Nationality, Species Membership (2006), and later in Justice for Animals (2023), proposes a third path based on the capabilities approach (capabilities approach), originally developed by Amartya Sen.

For Nussbaum, each animal species has a characteristic set of capabilities — forms of flourishing that are proper to it. The human ethical obligation is not to impede the flourishing of these capabilities: not merely to avoid inflicting suffering, but to create conditions for animals to live according to their nature. The capabilities approach is richer than the suffering criterion because it recognizes that animals have lives with their own complexity and value, not reducible to the absence of pain.

Nussbaum also criticizes Singer for his willingness, within utilitarianism, to offset deaths with new births of equally happy beings — the so-called “replaceability argument.” For Nussbaum, each animal is an individual with unique and non-interchangeable value.

Christine Korsgaard: Kant and Animals

Christine Korsgaard, philosopher at Harvard, in Fellow Creatures: Our Obligations to the Other Animals (2018), develops a defense of animals from Kantian premises — apparently the most resistant to this extension, given the central role Kant assigns to rationality.

Korsgaard’s argument is that what grounds moral value is not rationality as an abstract capacity, but the fact that every conscious being has a standpoint from which things matter — a “good of one’s own.” Animals have this good of their own: suffering is bad for them, pleasure is good for them. This is sufficient grounds for them to be ends in themselves.

Practical Implications

Animal Experimentation

The ethical debate over animal experimentation distinguishes different uses: biomedical research, cosmetics testing, education, basic research. While Singer accepts that some experiments may be justified in extreme cases (provided benefits outweigh costs and no alternatives exist), Regan rejects them categorically. In practice, the debate has driven the development and adoption of alternative methods (in vitro, computational models, organoids) and legislation requiring minimization of suffering and replacement by alternative methods when available (the so-called “3Rs”: Replacement, Reduction, Refinement).

Factory Farming and Diet

Industrial meat production involves practices — confinement in extremely reduced spaces, mutilations without anesthesia, separation of offspring from mothers, stressful transport, slaughter — that entail suffering on a massive scale. Singer argues that the consumer who purchases industrially farmed animal products is morally complicit in that suffering.

Singer’s position on diet is pragmatic: veganism is the lifestyle that causes the least suffering given the current food system, and is therefore preferable. But Singer does not make veganism an absolute imperative — what matters is reducing suffering, not adhering rigidly to a rule.

Legislation and Rights

In several countries, pressure from the animal rights movement has resulted in more protective legislation: the ban on battery cages for laying hens in the EU (2012), bans on cosmetics testing on animals, and legal recognition of animal sentience in documents such as the Treaty of Lisbon, which in 2007 recognized animals as “sentient beings.” Some countries have recognized limited personhood for great apes in specific contexts.

Objections and Responses

The “Line” of Sentience

A frequent objection is: where to draw the line? If all sentient beings have moral consideration, does this extend to insects? To crustaceans? To fish? Singer responds that uncertainty about the sentience of less complex organisms does not invalidate the argument, but demands caution proportional to the probability of sentience.

Rights vs. Interests

Some philosophers (such as R. G. Frey, in Interests and Rights, 1980) argue that animals do not have interests in the full sense because they lack linguistically articulated beliefs and desires, and therefore cannot have rights. Singer and Regan respond that interests do not presuppose language — suffering is suffering regardless of verbal articulation.

Excessive Practical Consequences

Critics such as Peter Carruthers argue that extending full rights to animals would lead to impractical consequences and would conflict with other important moral values. Singer responds that the point is not to treat animals exactly like humans, but to give proportional weight to their interests — which, by itself, would imply radical changes in current practices.

Concluding Remarks

The debate over the moral status of animals is one of the most vibrant in contemporary applied ethics. Singer, Regan, Nussbaum, and Korsgaard offer distinct philosophical architectures — utilitarian, deontological, capabilities-based, and Kantian — that converge on the conclusion that current practices of animal treatment are morally indefensible in their scale and cruelty.

The central philosophical question remains open: what is the correct criterion of moral inclusion? The answer to this question determines not only how we should treat animals, but how we understand the very foundations of ethics itself.

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