Another reason to deny that animals deserve direct concern arises from the belief that animals are not conscious, and therefore have no interests or well-being to take into consideration when considering the effects of our actions. Someone that holds this position might agree that if animals were conscious then we would be required to consider their interests to be directly relevant to the assessment of actions that affect them. However, since they lack a welfare, there is nothing to take directly into account when acting.
One of the clearest and most forceful denials of animal consciousness is developed by Rene Descartes (1596-1650), who argues that animals are automata that might act as if they are conscious, but really are not so (Regan and Singer, 1989: 13-19). Writing during the time when a mechanistic view of the natural world was replacing the Aristotelian conception, Descartes believed that all of animal behavior could be explained in purely mechanistic terms, and that no reference to conscious episodes was required for such an explanation. Relying on the principle of parsimony in scientific explanation (commonly referred to as Occam’s Razor) Descartes preferred to explain animal behavior by relying on the simplest possible explanation of their behavior. Since it is possible to explain animal behavior without reference to inner episodes of awareness, doing so is simpler than relying on the assumption that animals are conscious, and is therefore the preferred explanation.
Descartes anticipates the response that his reasoning, if applicable to animal behavior, should apply equally well to human behavior. The mechanistic explanation of behavior does not apply to human beings, according to Descartes, for two reasons. First, human beings are capable of complex and novel behavior. This behavior is not the result of simple responses to stimuli, but is instead the result of our reasoning about the world as we perceive it. Second, human beings are capable of the kind of speech that expresses thoughts. Descartes was aware that some animals make sounds that might be thought to constitute speech, such as a parrot’s “request” for food, but argued that these utterances are mere mechanically induced behaviors. Only human beings can engage in the kind of speech that is spontaneous and expresses thoughts.
Descartes’ position on these matters was largely influenced by his philosophy of mind and ontology. According to Descartes, there are two mutually exclusive and jointly exhaustive kinds of entities or properties: material or physical entities on the one hand, and mental entities on the other. Although all people are closely associated with physical bodies, they are not identical with their bodies. Rather, they are identical with their souls, or the immaterial, mental substance that constitutes their consciousness. Descartes believed that both the complexity of human behavior and human speech requires the positing of such an immaterial substance in order to be explained. However, animal behavior does not require this kind of assumption; besides, Descartes argued, “it is more probable that worms and flies and caterpillars move mechanically than that they all have immortal souls” (Regan and Singer, 1989: 18).
More recently, arguments against animal consciousness have been resurfacing. One method of arguing against the claim that animals are conscious is to point to the flaws of arguments purporting to claim that animals are conscious. For example, Peter Harrison has recently argued that the Argument from Analogy, one of the most common arguments for the claim that animals are conscious, is hopelessly flawed (Harrison, 1991). The Argument from Analogy relies on the similarities between animals and human beings in order to support the claim that animals are conscious. The similarities usually cited by proponents of this argument are similarities in behavior, similarities in physical structures, and similarities in relative positions on the evolutionary scale. In other words, both human beings and animals respond in the same way when confronted with “pain stimuli”; both animals and human beings have brains, nerves, neurons, endorphins, and other structures; and both human beings and animals are relatively close to each other on the evolutionary scale. Since they are similar to each other in these ways, we have good reason to believe that animals are conscious, just as are human beings.
Harrison attacks these points one by one. He points out that so-called pain-behavior is neither necessary nor sufficient for the experience of pain. It is not necessary because the best policy in some instances might be to not show that you are in pain. It is not sufficient since amoebas engage in pain behavior, but we do not believe that they can feel pain. Likewise, we could easily program robots to engage in pain-behavior, but we would not conclude that they feel pain. The similarity of animal and human physical structures is inconclusive because we have no idea how, or even if, the physical structure of human beings gives rise to experiences in the first place. Evolutionary considerations are not conclusive either, because it is only pain behavior, and not the experience of pain itself, that would be advantageous in the struggle for survival. Harrison concludes that since the strongest argument for the claim that animals are conscious fails, we should not believe that they are conscious.
Peter Carruthers has suggested that there is another reason to doubt that animals are conscious Carruthers, 1989, 1992). Carruthers begins by noting that not all human experiences are conscious experiences. For example, I may be thinking of an upcoming conference while driving and not ever consciously “see” the truck in the road that I swerve to avoid. Likewise, patients that suffer from “blindsight” in part of their visual field have no conscious experience of seeing anything in that part of the field. However, there must be some kind of experience in both of these cases since I did swerve to avoid the truck, and must have “seen” it, and because blindsight patients can catch objects that are thrown at them in the blindsighted area with a relatively high frequency. Carruthers then notes that the difference between conscious and non-conscious experiences is that conscious experiences are available to higher-order thoughts while non-conscious experiences are not. (A higher-order thought is a thought that can take as its object another thought.) He thus concludes that in order to have conscious experiences one must be able to have higher-order thoughts. However, we have no reason to believe that animals have higher-order thoughts, and thus no reason to believe that they are conscious.