Narrator: Imagine you are walking past a shallow pond when you see a small child has fallen in and is in danger of drowning. You are the only person around. You know you can easily wade in and pull the child out, but doing so will ruin your expensive new shoes and make you late for an important meeting. Do you have a moral obligation to save the child? Most people would say yes, without hesitation. The cost of the shoes is insignificant compared to the value of a human life. But what if that child isn't right in front of you? What if they are thousands of miles away, dying from a preventable disease that could be cured for the cost of those same shoes? Does distance change our moral calculus?

This is the kind of disarmingly simple yet profoundly challenging question at the heart of Peter Singer's seminal work, Practical Ethics. The book is a rigorous and often controversial journey that takes this basic ethical intuition—that we should prevent great harm when we can do so at little cost to ourselves—and applies it consistently to the most complex moral dilemmas of our time, from animal rights to global poverty.

Narrator: At its core, Singer’s ethical framework is built on a single, powerful principle: the equal consideration of interests. This does not mean that all beings must be treated identically. Instead, it means that in our moral deliberations, the like interests of any being should be given the same weight as the like interests of any other being.

Singer illustrates this with a thought experiment. Imagine two victims of an earthquake. One has a crushed leg and is in agony, while the other has a minor gash on their thigh and is in slight pain. A rescuer has only two shots of morphine. Equal treatment would suggest giving one shot to each person. But equal consideration of their interests—specifically, their interest in avoiding pain—demands a different course of action. The single shot would do little for the person in agony, but giving both shots to them would provide immense relief. Therefore, to achieve the greatest reduction in suffering, the rescuer should give both shots to the more severely injured person. This principle of impartially weighing interests, especially the interest in avoiding suffering, becomes the bedrock for all of Singer's subsequent arguments.

Narrator: Singer famously extends the principle of equal consideration beyond the human species, arguing that limiting it to humans is a form of prejudice he calls "speciesism." He contends that the boundary of our moral concern should not be intelligence, rationality, or species, but the capacity for suffering. As the philosopher Jeremy Bentham wrote, "The question is not, Can they reason? nor Can they talk? but, Can they suffer?"

If a being can suffer, it has an interest in not suffering, and that interest must be included in our moral calculus. To ignore this interest simply because the being is not a member of our species is as arbitrary and indefensible as ignoring it based on race or sex. The book points to the brutal realities of factory farming and animal experimentation as clear examples of institutionalized speciesism. In these systems, the profound suffering of billions of sentient animals is routinely subordinated to relatively trivial human interests, such as a preference for the taste of meat or the pursuit of uncertain scientific knowledge, as seen in H.F. Harlow's cruel maternal deprivation experiments on monkeys.

Narrator: To tackle the ethics of taking life, Singer introduces a critical distinction between being a "human being" and being a "person." A human being is a biological category, a member of the species Homo sapiens. A "person," in the philosophical sense, is a rational, self-aware being who can conceive of themselves as existing over time, with a past and a future.

This distinction is vital because the reasons for not killing a person are different and stronger than the reasons for not killing a merely sentient being. Killing a person thwarts their future-oriented desires and violates their autonomy. Singer argues that some non-human animals, such as great apes, dolphins, and elephants, show compelling evidence of self-awareness and planning, qualifying them as persons. The chimpanzee Washoe, who learned sign language and, when asked who the image in the mirror was, signed "Me, Washoe," provides a powerful example. Conversely, a human embryo or a person in a persistent vegetative state is a member of our species but is not a "person" in this sense. This reframes the debate: the moral gravity of taking a life should depend on the characteristics of the individual, not its species membership.

Narrator: Applying the concept of personhood leads to some of the book's most controversial conclusions. Since a fetus is a human being but not a person—lacking rationality, self-awareness, and a sense of the future—Singer argues that its claim to life is not equivalent to that of a person. Therefore, the arguments against killing a person do not apply to abortion.

More controversially, this same logic applies to newborn infants. Since infants are not yet rational or self-aware, Singer concludes that the life of a newborn has less value than the life of a person, and that nonvoluntary euthanasia for a severely disabled infant, whose life would be filled with suffering, can be justifiable. On the other end of life, the book defends voluntary euthanasia. For a person who is suffering from a terminal illness and rationally chooses to end their life, respecting their autonomy means allowing them to do so. The case of Dr. Timothy Quill, who prescribed barbiturates to his patient Diane so she could end her life on her own terms when her leukemia became unbearable, illustrates a compassionate response grounded in respect for a person's autonomous choice.

Narrator: Singer returns to the "drowning child" scenario to build his case for our obligations to those in extreme poverty. The principle is clear: if it is in our power to prevent something very bad from happening, without thereby sacrificing anything of comparable moral significance, we ought to do it.

He argues that this principle applies directly to global poverty. The affluent live with luxuries—expensive clothes, entertainment, gourmet food—that are not morally significant when weighed against the life of a person dying from malnutrition or a preventable disease. Organizations like GiveWell.org estimate that a life can be saved in a developing country for a few thousand dollars or less. For most people in the developed world, donating this amount would not require sacrificing anything essential. Therefore, just as we are obligated to save the drowning child in the pond, we are obligated to donate a significant portion of our income to effective aid agencies. This is not an act of charity, but a fundamental moral duty.

Narrator: The book frames climate change not just as an environmental problem, but as a profound ethical failure. The atmosphere is a finite resource—a sink that can only absorb a limited amount of greenhouse gases. Wealthy, industrialized nations have used a disproportionate share of this resource for over a century, primarily for what Singer calls "luxury emissions."

This overuse is now causing direct harm to the world's most vulnerable populations, who have contributed the least to the problem. Rising sea levels are already swallowing islands in the Ganges delta, displacing families who have nowhere else to go. Meanwhile, wealthy nations like the Netherlands and Australia can afford to build expensive sea walls and desalination plants to adapt. Singer argues that from an ethical standpoint, the continued high emissions of rich nations constitute an act of aggression against the poor. A just solution would require wealthy nations to take historical responsibility and drastically cut their emissions, allowing developing nations a fair share of the remaining atmospheric capacity for their "subsistence emissions."

Narrator: The single most important takeaway from Practical Ethics is that a consistent, reason-based approach to morality demands a radical re-evaluation of our most deeply held beliefs and behaviors. Singer dismantles the comfortable barriers we erect—between humans and animals, between killing and letting die, between our neighbors and distant strangers—and forces us to confront the logical consequences of our own ethical intuitions. The book argues that a truly ethical life is one that extends the principle of equal consideration to all sentient beings, challenging the speciesism, nationalism, and consumerism that define modern life.

The ultimate challenge of Practical Ethics is not merely intellectual; it is profoundly practical. It doesn't just ask us to think differently, but to live differently. After following the chain of logic, the final, lingering question is not whether Singer's conclusions are shocking, but whether we can find a rational justification for not acting on them.