Australian philosopher Peter Singer's book Animal Liberation, first published in 1975, has become "the Bible" of the animal rights movement. A second, revised edition was issued in 1990. All page citations here are to that edition.

Although Singer is himself a utilitarian, and has published widely in professional philosophy journals, this book was intended for popular consumption and so Singer avoided as many controversial points in ethical theory as possible.

The first chapter of the book, titled "All Animals are Equal," lays out four minimal philosophical commitments, which he thinks any reader will agree to. He bases his subsequent arguments against research on animals, animal agriculture, hunting and trapping, etc. on these minimal commitments.

1. The concept of equality: "Equality is a moral idea, not an assertion of fact" (1990, p. 4). That is, when we say that "all humans are equal," we do not assert that they are in fact equal in intelligence, capabilities, size, etc. Rather, we assert that they deserve equal consideration of interests.

2. The principle of equal consideration of interests: "[T]he 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" (1990, p. 5 [emphasis added]). Note that equal consideration of interests does not imply identical treatment. For example, equal consideration of men's and women's interests won't imply that men should have a right to elective abortion.

3. The definition of "speciesism": "Speciesism . . . is a prejudice or attitude of bias toward the interests of members of one's own species and against those of members of other species" (p. 6). Speciesism, racism and sexism each have the same basic logic -- ignoring or differentially weighting the similar interests of member of different groups:

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   Racists	Ignore or differentially	Blacks, etc.
   Sexists	weight the	women
   Speciesists	similar interests of	animals

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4. Sentience is necessary & sufficient for having interests:

   • Necessary: "A stone does not have interests because it cannot suffer," and

   • Sufficient: "If a being suffers there can be no moral justification for refusing to take that suffering into consideration" (p. 8).

The upshot: If Singer is right that sentience is a sufficient condition for having interests, and that all interests warrant equal consideration, then all sentient animals are in his sense equal, whether they are members of our species or not.

Obviously, which species' members even have interests, let alone what interests are shared across species boundaries, are philosophically and empirically complex questions. This question is addressed to some extent later in this lecture, but you can skip straight to the relevant material by clicking here.

Singer argues that a variety of common practices are speciesist, including:

1. Agriculture: veal & poultry industries, other slaughter industries, dairy industry

2. Science: cosmetic & product safety testing, education, pure research, medical research

3. Recreation and entertainment: circuses & rodeos, pet overpopulation, keeping of pets

4. Wildlife: sport hunting, therapeutic hunting, subsistence hunting