Weak Analogy

Bertha Alvarez Manninen

The eye appears to have been designed; no designer of telescopes could have done better. How could this marvelous instrument have evolved by chance, through a succession of random events? Many people in Darwin’s day agreed with theologian William Paley, who commented, “There cannot be a design without a designer.”

Robert Jastrow (in Life—How Did It Get Here?)

Appeal to analogies can be a successful tool when constructing strong arguments.

(1) Example X is relevantly similar to example Y.

(2) P follows from X.

(3) Therefore, P follows from Y.

Whether or not an argument from analogy is strong depends on whether premise 1 is true - that is, are X and Y sufficiently and relevantly similar so that you can infer that P follows from Y just because P follows from X. The focus, therefore, should be on the reasons P follows from X and whether those reasons also apply to Y. As Patrick Hurley writes, the weak analogy fallacy “occurs when the conditions of an argument depend on an analogy

(or similarity) that is not strong enough to support the conclusion” (Hurley 2008, 716). In the citation above, Paley argues that the creation of human artifacts is sufficiently similar to the creation of human organisms (and to the universe in general, as he argues in his 1802 work, Natural Theology) to infer the existence of a creator. As we shall see below, philosopher David Hume has given reasons to think arguments of this sort commit the weak analogy fallacy.

Often, vegetarians and vegans will hear the following argument from analogy in defense of carnivorism: “Animals eat each other in nature, so it’s permissible for us to eat them as well.” The logical structure of this retort to vegetarianism is:

(1) Animals eat each other in nature (example X).

(2) Carnivores eat animals (example Y).

(3) It is permissible for animals to eat each other in nature (P follows from X).

(4) Therefore, it is permissible for us to eat animals (P follows from Y).

In order for this argument to be successful, there must be relevant similari­ties between animals’ eating each other in nature and humans’ eating ani­mals in our industrialized world. What we find, however, is that there are very few similarities and many more dissimilarities. While both humans and animals do indeed eat other animals for nutrition, unlike animals in nature, humans have plenty of other options for adequate nutrition that do not involve eating sentient creatures. Moreover, factory farming entails much more suffering for the animal than a quick death at the jaws of a predator and has detrimental health and environmental implications not present when animals hunt each other. Finally, we do not typically look to animals for moral guidance - male lions, when taking over a pride, will kill the cubs of the previous male lion in order to breed with the lionesses, but we wouldn’t use this example to justify a step-father killing his step-children. Clearly, then, this is an example of the weak analogy fallacy.

In the quotation above, Robert Jastrow is appealing to an argument that many theists often bring up as evidence of God’s existence. We know that complex objects, such as a telescope, have creators and cannot come together on their own. The universe, the argument goes, is similarly complex and, therefore, must also have a creator. This argument - called the design or teleological argument - has been put forth by philosophers for millennia. Many have argued, however, that for various reasons it is not possible to compare the creation of artifacts (like a telescope or a watch) to the creation of a whole universe. For example, Hume notes that while we have empirical exposure to artifacts’ being created, we have no similar exposure to uni­verses’ being created and so we cannot conclude anything about the creation of the latter based upon the former.

As mentioned above, analogies can indeed be successfully used for making strong arguments. They key is to ensure that the things you are comparing are relevantly similar so that you can draw viable inferences from those similarities. This does not mean that they will be similar in every way - when making comparisons between objects or states of affairs, it is inevitable that there will be some differences. The important thing is to make sure that the cases or things you are comparing are similar in the right way.

Take, for a further example, Judith Jarvis Thomson’s well-discussed example of the famous violinist. Doctors have, without your permission, attached a famous violinist to your body for nine months in order to sustain and save his life. Thomson compares this to having an unwanted pregnancy. There are both similarities and differences between the violinist example and the typical case of an unplanned pregnancy. Individuals who are not convinced by Thomson’s argument will likely maintain that the dissimilarities between the two are sufficient to render her argument flawed; those who agree with Thomson will likely maintain that the similarities are indeed sufficient to conclude that a woman is no more obligated to sustain fetal life than you are to sustain the violinist.

In the past, some philosophers have argued that animals do not feel any pain. This has typically been defended by appealing to their (alleged) non- rational nature. However, we can feel rather confident in maintaining that animals (especially mammals) do indeed feel pain because their pain behavior and central nervous systems are relevantly similar to those of humans. While it may be true that animals lack robust rational properties, that is not relevant for concluding that they lack the capacity to feel pain, lest we also maintain that human infants or humans with severe mental disabilities also lack the capacity to feel pain given their lack of robust rational proper­ties.

Nearly all the external signs that lead us to infer pain in other humans can be seen in other species, especially the species most closely related to us - the species of mammals and birds. The behavioral signs include writhing, facial contortions, moaning, yelping or other forms of calling, attempts to avoid the source of the pain, appearance of fear at the prospect of its repetition, and so on. In addition, we know that these animals have nervous systems very like ours, which respond physiologically like ours do when the animal is in circum­stances in which we would feel pain: an initial rise of blood pressure, dilated pupils, perspiration, an increased pulse rate, and, if the stimulus continues, a fall in blood pressure [...]. We also know that the nervous systems of other animals were not artificially constructed - as a robot might be artificially constructed - to mimic the pain behavior of humans. The nervous systems of animals evolved as our own did, and in fact the evolutionary history of human beings and other animals, especially mammals, did not diverge until the central features of our nervous systems were already in existence (Singer 1990, 11-12).

By focusing on these similarities between animals and humans, and by argu­ing that these similarities are indeed relevant to the issue at hand, Singer presents a strong argument from analogy in favor of the conclusion that animals are indeed sentient beings.

References

Hurley, Patrick. 2008. A Concise Introduction to Logic. Belmont, CA: Wadsworth Cengage Learning.

Jastrow, Robert. 1985. Life—How Did It Get Here? By Evolution or by Creation?. New York: Watch Tower.

Singer, Peter. 1990. Animal Liberation. New York, NY: Avon Books.

Thomson, Judith Jarvis. 1971. “A Defense of Abortion.” Philosophy and Public Affairs 1(1): 47-66.