Although he does not explicitly endorse the theory in Animal Liberation, in his professional writings, Singer is one of the best-known defenders of utilitarianism in ethical theory. Although the term is used in various ways in day-to-day speech, ethical theorists define utilitarianism specifically as:
Utilitarianism =df the view that morally right actions and institutions maximize aggregate happiness.
Note several things about this definition:
In ethical theory, a "hedonist" is not someone who excessively pursues pleasures, but rather someone who holds a particular belief about what has intrinsic value, namely the view that pleasure is the only intrinsically good thing and pain (suffering) the only intrinsically bad thing. When a utilitarian defines "happiness" in hedonistic terms, the resulting view is called hedonistic utilitarianism:
Hedonistic utilitarianism =df the view that morally right actions and institutions maximize aggregate pleasure and/or minimize aggregate pain.
On the hedonistic conception, an individuals are happy to the extent that they experience pleasure and avoid pain, although hedonists generally construe "pleasure" and "pain" very broadly, to include not only physical pleasures and pains (e.g., those accompanying orgasms and third-degree burns) but various kinds of pleasant and unpleasant psychological states (e.g. glee, exhilaration, tension, and nervousness).
The most famous exponent of this view was John Stuart Mill, who further held that there are qualitative differences between intellectual pleasures and bodily pleasures.
The most common alternative definition of happiness is in terms of preference satisfaction. On this view, individuals are happy to the extent that achieve and maintain an integrated satisfaction of their preferences. In this context, "preferences" include "desires," "plans," "projects," and any other consciously pursued goals.
When a utilitarian defines "happiness" this way, the resulting view is called preference utilitarianism:
Preference utilitarianism =df the view that morally right actions and institutions maximize aggregate preference satsifaction and/or minimize aggregate preference frustration or denial.Note:
Since he wrote Animal Liberation for popular consumption, we need to look elsewhere for a careful statement of his philosophy. A good place to look is his Practical Ethics (Cambridge University Press, 1993).
There he emphasizes that he is a thorough-going utilitarian, but for the kinds of reasons given above, he thinks we need to conceive of happiness differently for animals who can conceive of their own future and those who cannot.
So Singer's view is complex:
Singer cites research which he thinks clearly shows that the great apes (chimpanzees, gorillas, and orangutans) have sufficiently forward-looking desires to qualify for a preference-based analysis of their happiness (Practical Ethics, pp. 111-16, 118, and 132), and, without saying what specific research leads him to these conclusions, that fish and chickens do not (ibid., pp. 95, 133).
Singer argues that this division makes "lower" animals "replaceable" in the following sense. When an animal without a robust sense of its future is killed painlessly, the only sense in which it has been harmed is insofar as it has been deprived of future opportunites for pleasure. But from the utilitarian point of view, this loss to aggregate happiness can be remedied by replacing the deceased individual with an equally happy individual. So, for instance, if there are three happy chickens in the world:
If we kill one painlessly and replace it with an equally happy chicken:
Then there has been no loss to aggregate happiness.
Singer recognizes that this suggests an argument in support of a sufficiently humane form of slaughter-based agriculture, but he argues that environmental effects and nutritional inefficiencies "greatly weaken the replaceability argument as a defence of meat-eating" (Practical Ethics, pp. 121-22).