On indirect theories, animals do not warrant our moral concern on their own, but may warrant concern only in so far as they are appropriately related to human beings. The various kinds of indirect theories to be discussed are Worldview/Religious Theories, Kantian Theories, Cartesian Theories, and Contractualist Theories. The implications these sorts of theories have for the proper treatment of animals will be explored after that. Finally, two common methods of arguing against indirect theories will be discussed.
Some philosophers deny that animals warrant direct moral concern due to religious or philosophical theories of the nature of the world and the proper place of its inhabitants. One of the earliest and clearest expressions of this kind of view comes to us from Aristotle (384-322 B.C.E.). According to Aristotle, there is a natural hierarchy of living beings. The different levels are determined by the abilities present in the beings due to their natures. While plants, animals, and human beings are all capable of taking in nutrition and growing, only animals and human beings are capable of conscious experience. This means that plants, being inferior to animals and human beings, have the function of serving the needs of animals and human beings. Likewise, human beings are superior to animals because human beings have the capacity for using reason to guide their conduct, while animals lack this ability and must instead rely on instinct. It follows, therefore, that the function of animals is to serve the needs of human beings. This, according to Aristotle, is “natural and expedient” (Regan and Singer, 1989: 4-5).
Following Aristotle, the Christian philosopher St. Thomas Aquinas (1225-1274) argues that since only beings that are rational are capable of determining their actions, they are the only beings towards which we should extend concern “for their own sakes” (Regan and Singer, 1989: 6-12). Aquinas believes that if a being cannot direct its own actions then others must do so; these sorts of beings are merely instruments. Instruments exist for the sake of people that use them, not for their own sake. Since animals cannot direct their own actions, they are merely instruments and exist for the sake of the human beings that direct their actions. Aquinas believes that his view follows from the fact that God is the last end of the universe, and that it is only by using the human intellect that one can gain knowledge and understanding of God. Since only human beings are capable of achieving this final end, all other beings exist for the sake of human beings and their achievement of this final end of the universe.
Remnants of these sorts of views remain in justifications for discounting the interests of animals on the basis of the food chain. On this line of thought, if one kind of being regularly eats another kind of being, then the first is said to be higher on the food chain. If one being is higher than another on the food chain, then it is natural for that being to use the other in the furtherance of its interests. Since this sort of behavior is natural, it does not require any further moral justification.