The Translation of the Book Animal Liberation — and Key Concepts

By Marly Winckler

In 2025, Peter Singer’s book Animal Liberation completes 50 years since its first edition, published in 1975. Over these decades, the work has become a fundamental reference for the contemporary animal-rights movement, influencing activists, researchers, and public policies around the world.

In this article, I briefly describe the process of translating the book into Portuguese and present its main philosophical concepts, as well as some of the developments that Singer expands on in his recent work Animal Liberation Now.

This article is based on the presentation I gave for the 7th Summer Course on Animal Rights organized by the Observatory for Ecological Justice (OJE) research group, at the invitation of professors Letícia Albuquerque and Paula Brugger, whose central theme of reflection was the 50th anniversary of the publication of Peter Singer’s Animal Liberation.

Meeting Peter Singer and the path to the translation

My first personal contact with Peter Singer took place in 1994, during the 31st World Vegetarian Congress of the International Vegetarian Union (IVU), held in The Hague, the Netherlands. It was also my first major international event within the movement. There, I met important figures such as Alex Hershaft (FARM – Farm Animal Rights Movement), Howard Lyman (author of Mad Cowboy), and Helen Nearing, who was associated with the back-to-the-land movement and a simpler, more self-sufficient lifestyle.

On that occasion, I expressed to Peter Singer my interest in translating Animal Liberation. When I returned to Brazil, I tried to make the publication viable through a publishing house in Rio de Janeiro with which I was working. The proposal was rejected: at the time — in the mid-1990s — the subject was considered “too heavy,” “disturbing,” and without commercial potential.

Almost ten years later, the publishing house Editora Lugano contacted me with the intention of releasing the work in Portuguese. Finally, between 2003 and 2004, I completed the translation of the then-current edition of Animal Liberation, which became the first Brazilian edition of Libertação Animal. During this period, I was already working within IVU as Latin American Coordinator and organizing the 36th World Vegetarian Congress, held in 2004 at Costão do Santinho, in Florianópolis. The formal creation of the Brazilian Vegetarian Society (SVB), in 2003, took place in this same context.

Curiously, a few years later, Editora Campus — which had initially shown no interest in the topic — invited me either to write the preface or to review the translation of another book by Singer, The Ethics of What We Eat. And two editors with whom I worked during that process eventually became vegetarians, which illustrates the transformative power of engaging more deeply with these arguments.

Animal Liberation (1975): context and proposal

Animal Liberation was first published in 1975 and is widely recognized as a founding milestone of the modern animal-rights movement. The book does not argue for “rights” in the strictly legal sense; rather, it develops a new ethical framework grounded in:

• sentience (the capacity to suffer and feel pleasure);

• equal consideration of interests between humans and animals;

• a critique of speciesism.

Beyond its philosophical argumentation, Singer provides detailed descriptions of industrial livestock production and laboratory experimentation. Translating the chapters in which he describes confinement, mutilations, and the suffering of animals in intensive systems was particularly difficult; however, it is precisely this combination of ethical analysis and factual description that gave the book its lasting impact.

Singer did not “tour farms” for his original research. Instead, he drew on reports, technical manuals, and publications from the agricultural and research industries themselves, consulting libraries extensively. In other words, his sources were largely the descriptions produced by farmers, researchers, and technicians whose goal was to increase productivity — not to expose cruelty. Singer then reorganized and interpreted this material in the light of a systematic moral reflection.

Key concepts of Animal Liberation

1. Speciesism

The central concept of the book is speciesism, defined as moral discrimination based on species. Just as with racism and sexism, speciesism is seen as an unjustifiable prejudice: to consider human interests necessarily more important simply because they belong to our species is, for Singer, arbitrary.

The term speciesism was coined in 1970 by the British psychologist Richard D. Ryder. Singer adopts the expression, gives it philosophical grounding, and projects it internationally, making the concept a central element in contemporary ethical debate.

2. Sentience and Bentham’s question

The moral criterion proposed by Singer is sentience: the capacity to suffer and to feel pleasure. He returns to Jeremy Bentham’s famous formulation (1789):

The question is not, “Can they reason?” or “Can they talk?” but “Can they suffer?”

Bentham argues that it is the capacity to suffer — and not intelligence or language — that grounds moral consideration. Singer turns this intuition into the core of his practical philosophy: every being capable of suffering has morally relevant interests.

3. Equal consideration of interests

From there, Singer formulates the principle of equal consideration of interests. It does not mean treating all beings in exactly the same way, but rather assigning equal weight to similar interests. If dogs, pigs, and human beings all have an interest in avoiding pain, that interest must count in the same way when we make moral decisions.

4. Industrial animal agriculture as the greatest source of avoidable suffering

One of the book’s main targets is industrial animal agriculture. Singer describes:

• extreme confinement;

• mutilations without anesthesia;

• deprivation of movement;

• chickens and pigs unable to turn around or walk;

• intense psychological suffering.

His argument is that consuming animal products, under current conditions, causes severe and unnecessary suffering, since viable dietary alternatives exist.

5. Animal experimentation

The author criticizes most uses of animals in laboratories, especially when they:

• involve intense and prolonged pain;

• fail to produce real benefits;

• would not be considered acceptable if carried out on humans with similar cognitive capacities (such as infants or people with profound disabilities).

Singer defends a criterion of moral consistency: if an experiment cannot ethically be performed on humans in a given condition, there is no sufficient moral justification to perform it on animals with comparable sensitivity.

6. Preference utilitarianism

His philosophical foundation is preference utilitarianism: we should act so as to minimize suffering and maximize well-being, taking into account the preferences and interests of all beings capable of suffering — human and nonhuman. He updates the classical utilitarian tradition (Bentham, John Stuart Mill), explicitly extending the moral circle beyond the human species.

7. Veganism as an ethical consequence

If it is possible to avoid grave and unnecessary suffering, Singer concludes, then we have a moral duty to do so. Veganism thus appears not as an identity or “lifestyle,” but as a practical and coherent consequence of rejecting speciesism and adopting an ethics based on sentience.

8. Expansion of the moral circle

Inspired by Darwinian ideas, Singer proposes the metaphor of the expanding moral circle: historically, human ethics would have moved outward from family to tribe, to nation, and ultimately to humanity as a whole. Animal Liberation is a call to extend that circle to all sentient beings.

He later develops this idea in works such as The Expanding Circle.

Animal Liberation Now (2023): a 50-year reassessment

In the revised and expanded edition Animal Liberation Now (2023), Singer reassesses the impact of the original book and the development of the animal cause. The preface presents an ambivalent picture: significant progress, but also regression on a global scale.

Advances 

Among the advances, Singer highlights:

• the growth and professionalization of animal-protection organizations;

• the approval of referendums and laws against extreme forms of confinement, especially in some U.S. states and European countries;

• the growing legal recognition of animals as sentient beings (for example, in the foundational treaty of the European Union);

• cultural change: the media now treats the topic with greater seriousness;

• the spread of the term “vegan,” once almost unknown and now present on menus, labels, and in public spaces worldwide.

Setbacks and worsening conditions

On the other hand, Singer shows that the situation of animals has worsened in absolute terms. The total number of animals exploited and killed has increased dramatically. China appears as a striking example: the world’s largest producer of pigs and a major producer of poultry, with highly concentrated intensive systems, including so-called “skyscraper farms” — multi-story buildings that house millions of animals in severe confinement.

Today, it is estimated that about 83 billion mammals and birds are bred and slaughtered annually for consumption, not counting fish and other aquatic animals. The vast majority live with no access to the outdoors.

At the same time, positive initiatives are also growing within China, such as entirely vegan restaurant chains, illustrating the paradoxical coexistence of expanding animal exploitation alongside expanding awareness and vegan options.

New knowledge about sentience

Singer also incorporates recent scientific research recognizing forms of sentience in fish, octopuses, lobsters, crabs, and other invertebrates. This further broadens the range of beings that should be included within our circle of moral concern. 

Animal agriculture and the climate crisis

Another central theme of the update is the relationship between animal agriculture and the climate crisis. Emissions from the agricultural sector — including associated deforestation, especially in the Amazon — make a significant contribution to global warming. Singer argues that a profound change in dietary patterns would have an impact comparable to a drastic reduction in the use of fossil fuels for transportation. Eliminating industrial animal agriculture would also reduce the incidence of cardiovascular disease and certain types of cancer linked to meat consumption.

Final considerations

Fifty years after its first edition, Animal Liberation remains one of the most influential books in contemporary ethics. The work:

• introduced concepts such as speciesism, sentience, and equal consideration of interests into the center of philosophical debate;

• systematically exposed the structural cruelty of industrial animal farming and animal experimentation;

• provided a rational foundation for veganism as an ethical requirement;

• contributed to the formation of an entire generation of activists and researchers.

At the same time, current data show that, despite growing awareness and the proliferation of vegan initiatives, animal exploitation continues on a massive scale, with profound environmental, health, and ethical consequences.

Singer’s central message remains valid: what is needed is a radical ethical reorientation, grounded in sentience and in respect for the intrinsic life of every animal. The translation and dissemination of these ideas across different languages and cultural contexts are part of this transformative effort — an effort for which Animal Liberation continues to serve as an indispensable point of reference.