What is Peter Singer’s Principle of Equal Consideration?

Peter Singer’s principle of equal consideration says that regardless of a sentient being’s race, sex, or species we ought to consider its interests no differently than any other.

Dec 28, 2023By Ryan Alexander, PhD Philosophy

peter singer on equal consideration


In Animal Liberation (1975) Australian moral philosopher Peter Singer argues that the moral consideration we owe non-human animals prohibits practices like factory farming and vivisection. The crux of his argument is a simple moral principle that he thinks already explains why other practices, like racism and sexism, are wrong. This is the principle of equal consideration.  In this article we’ll get a handle on what this principle says, why Singer believes it’s true, and its implications for our relationship with non-human animals.


The Principle of Equal Consideration Starts from a Puzzle

The Martyr of Equality, Isaac Cruikshank, 1793. Source: the National Gallery of Art
The Martyr of Equality, Isaac Cruikshank, 1793. Source: the National Gallery of Art


Human beings are a diverse species. In height, skin color, physical ability and intelligence we find remarkable variety, to mention just a few examples. Yet many of us subscribe to political and moral ideals of equality. We believe, among other things, in equality under the law, between the sexes, and at the ballot box where every vote counts just once. This presents a philosophical puzzle: in what sense are we equal—the same—if we’re different? 


It’s tempting to search for a distinction: perhaps the sense in which we’re different is not the sense in which we’re equal. This is Singer’s tack. He argues for these different senses by assuming something he’ll eventually reject: that our moral and political ideals of equality are statements of fact, that our equality consists in some property we all share (Singer, 3-4). For example, on this view when we say men and women are equal, or that everyone is equal before the law, we’re saying that these parties share some property that justifies their equal treatment. There is something they all have in common that underwrites their equality. 


But Singer goes on to reject this view. 

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The Principle of Equal Consideration Is Moral, not Factual

Un cours de morale moderne, Honoré Daumier, date unknown. Source: National Gallery of Art
Un Cours de Morale Moderne, Honoré Daumier, date unknown. Source: National Gallery of Art


Singer finds two problems with this argument (Singer, 3-4).  First, this shared property is elusive. No matter the candidate—intelligence, education, social status, whatever—equality between all won’t be found because there will always be outliers—human differences are legion. Another problem is that it invites discrimination. Imagine someone identifies intelligence as the shared property in question, and argues that moral status should differentially relate to level of intelligence: the smarter you are, the more you count. Singer finds this unacceptable because it’s discriminatory.


After all, it’s far from obvious why the interests of someone who is less intelligent should count for less. A parallel argument can be made using race: just because someone belongs to a particular race has no bearing on the moral consideration she’s owed. Properties like these just don’t confer moral standing one way or the other. 


The upshot, Singer tells us, is that “equality is a moral idea, not an assertion of fact. There is no logically compelling reason for assuming that a factual difference in ability between two people justifies any difference in the amount of consideration we give to their needs and interests. The principle of the equality of human beings is not a description of an alleged actual equality among humans: it is a prescription of how we should treat human beings” (Singer, 4-5; italics removed). 


Sentience is a Prerequisite for Moral Consideration

The March of Morality, William Heath, 1827-29. Source: Wikimedia Commons
The March of Morality, William Heath, 1827-29. Source: Wikimedia Commons


So Singer believes moral equality is prescriptive, not descriptive, because it’s not grounded in factual similarities between parties. Instead, it’s a moral ideal stipulating how we ought to treat each other. But more needs to be said. For without some factual basis for moral consideration it’s unclear how to distinguish moral and non-moral subjects altogether, like humans from sticks and stones. There must be a dividing line or philosophical ethics is overextended.  


Singer identifies this line as sentience—roughly the capacity to feel pleasure and pain (Singer, 7). The idea is that sentience is a prerequisite for having any interests at all, for unless things can go well or poorly for a being—as they surely can for a sentient being—it’s not clear in what way that being could prefer things one way over another. So interests are rooted in sentience, and this marks sentience as the line between moral and non-moral subjects.  


So far so good. But how does his appeal to sentience square with Singer’s claim that equality is not grounded in facts? Did he not just make the fact of sentience the shared property between all subjects who are proper members of the moral community? The answer lies in a proper understanding of the principle of equal consideration of interests. 


The Principle of Equal Consideration Enlarges the Moral Community

Iglesia de San Juan Bautista del Moral, Zarateman, 2015. Source: Wikimedia Commons
Iglesia de San Juan Bautista del Moral, Zarateman, 2015. Source: Wikimedia Commons


We said that the principle of equal consideration is moral, not factual, and that sentience is the necessary and sufficient condition to be candidate for such consideration. But we have not said what exactly the principle states. Here’s Singer: “the interests of every being affected by an action are to be taken into account and given the same weight as the like interests of any other being” (Singer, 5; emphasis mine). 


Importantly, this principle counsels equal consideration, not equal treatment. The difference is that equal consideration is extended to every being who, in virtue of being sentient, is a moral subject; equal treatment is extended to every being who’s a moral subject and has relevantly similar interests. For example, like all animals, we are interested in not suffering. Singer believes this entitles each of us—animals included—to equal consideration of this interest. But, unlike all animals, we are also interested in distinctly human endeavors, like meaningful work and social justice. These shared and distinctive interests entitle us to equal treatment, for example to not being discriminated against when applying to a job or when voting in an election. 


Tying these threads together, the result is that Singer’s principle of equal consideration enlarges the moral community. For no longer can the mere fact of being human, rational, or self-conscious justify discounting animals’ interest in not suffering. Instead, the like interests of every being are morally on par on pain of excluding a subject from moral consideration on the basis of irrelevancies, like its species, sex or race.

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By Ryan AlexanderPhD PhilosophyRyan holds a PhD in philosophy