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When we observe a dog wounded in a traffic accident, for instance, we infer that the dog must be in pain, based on the analogy between humans and dogs and what we know about humans. The structure of this piece of reasoning can be unpacked as follows: Dogs are analogous to humans. When humans are wounded, they experience pain. Therefore, it is reasonable to conclude that when dogs are wounded, they experience pain.

What are the fallacies and biases of analogical reasoning ?

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There is no fallacy, but it is not logically proven either. Rather, it is a defeasible argument.

There is no logical fallacy here, nor is there an informal fallacy. This argument is reasonable and likely to be persuasive. I personally find it persuasive.

However, while it is persuasive, it is not proof. This argument provides a reasonable reason to believe something, but it is not conclusive and leaves open the possibility that contrary arguments, especially contrary arguments which add new information could also be persuasive and perhaps more persuasive. For instance, while I don't know anything about neurology personally, quick Googling suggests that there are six primary areas of the brain which address pain. If close examination of a dog's brain shows that they lack anything analogous, that might at least persuade us that the argument you laid out should not be given persuasive weight. But, the fact that the argument you laid out is not absolutely conclusive does not mean it contains a fallacy and does not mean that it is not a persuasive argument.

More broadly, there are no fallacies or biases which are automatically inherent to analogical reasoning. Analogical reasoning is ubiquitous in law and policy discussions and frequently useful in many other areas.

However, specific analogical arguments may be examples of false analogies. "False analogy" is the name of an informal logical fallacy and essentially means that the analogical reasoning brought forward fails to account for relevant differences.

To look at your dog analogy, if you knew ahead of time that dogs lacked an analog for the relevant brain areas but you advanced your argument anyway without even mentioning that fact, then you would be committing the informal fallacy of a false analogy.

Also, while analogies can be useful, a specific analogy can be attacked by highlighting a disanalogy (essentially pointing out a relevant difference that could make it a false analogy, but it truly falls into that fallacy if the difference was known by the person making the argument ahead of time), pointing out unintended consequences of the analogy, or counter-analogy (essentially showing that a different analogy which is equally strong or stronger leads to a different inferred result). And of course, since an argument from analogy never provides logical certainty, you can always advance direct evidence that the conclusion simply is not true.

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They would be too many to list. Analogical reasoning fundamentally depends on our notion of similarity. The problem, however, as Goodman showed is that any two things can be considered to be similar with respect to certain attributes and dissimilar to others. It is completely context dependent and is arguably vacuous as a term. Any sentence of the form “A is similar to B” can be easily replaced by “A and B both share X attribute(s).” This more clearly gets at what we refer to by similarity without having to use a vacuous term. The problem can then be rephrased as: which attributes are more important than others? And here is where arbitrariness and assumptions can kick in.

Because of this, anything can be similar to anything else given a certain attribute hence pointing out the fundamental flaw in analogical reasoning. Note that this is the same reason why there is a problem in induction, but not just because we can’t know if the future will resemble the past. Before induction can even get off the ground, one must compare the new instance to past instances. How is this done? Using the notion of similarity. But as mentioned, similarity is ill defined, vacuous, and completely context dependent. The future always resembles the past and always does not resemble it with respect to certain attributes.

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Analogical Fallacies

  1. Irrelevant similarity: An essay has a head and body. A man has a head and body and is alive. Ergo, an essay is alive. Head and Body are irrelevant similarities. The fallacy of false analogy.

  2. Irrelevant dissimilarity: A dog has a tail. A human does not have a tail. Ergo, that dogs and animals are similar is a false analogy. Tails, yes for dogs and no for humans, is an irrelevant dissimilarity. Refutation failure of an analogical argument.

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