ECN 506 Chapter 11: Chapter 11

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4 Aug 2016
Chapter 11: Analogies
The nature and functions of analogy
- When one points out a similarity between two things, one draws an analogy between them.
- In literature analogies go by the name of similes and metaphors. Analogies are used in teaching
to illustrate or explain points or they make speech or writing more interesting.
- Medical research and archaeology are sciences which depend heavily on arguments from
- Archaeologists observe that people who are now living use items similar in form to those found
in archaeological excavations. On the basis of these observed similarities, archaeologists infer by
analogy that the prehistoric items were used in a similar way.
- Analogy plays an important role in moral reasoning. That is, when one claims that a certain act
deserves blame, one might want to show that the act is relevantly similar to other actions that are
quite clearly classified as blameworthy.
- When one concludes that things which are similar in observed ways are also similar in some
further as yet unobserved respect, one uses an argument from analogy.
- For example, analogical reasoning from the observed effects of birth control hormones on apes
(which are physiologically very similar to humans) can be used to conclude that birth control
pills may affect humans similarly.
- For an argument from analogy, a conclusion has to be drawn on the basis of an analogy.
- Govier calls the central topic, that is, the one mentioned in the conclusion, the primary subject,
and the one to which it is compared the analogue.
1. Form of arguments from analogy
- Many arguments by analogy take the following basic form:
Objects of type X have properties F, G, H, and so on.
Analogue: Objects of type Y have properties F, G, H, etc. and also an additional property Z.
Primary subject: Objects of type X have property Z as well.
- In the argument that concludes that birth control pills may affect human birth control,
properties F, G, H, etc. are the physiological properties that humans and apes have in common.
The further property Z of human birth control has been observed for apes and is inferred to hold
for humans as well.
- If one challenges the conclusions of such arguments, one usually mentions relevant
dissimilarities between the animals used in the experiment and human beings.
2. Standards for the strength of analogical arguments
- The strength of an analogy argument depends on the relevance of the similarities in the
premises (F, G, H) to the similarity stated in the conclusion (Z). One feature is relevant to
another feature, if the presence of the first increases (is positively relevant to) or decreases (is
negatively relevant to) the probability that the second feature will also be given.
- The degree of relevant similarity (or relevant dissimilarity) between the objects in the premises
(X and Y) and the conclusion is important in judging the strength of analogical arguments. The
greater the degree of relevant similarity is between the two types of objects (X and Y), the
stronger is the argument that the feature mentioned in the conclusion will also be shared.
- Other criteria for determining the strength of analogical arguments are the (a) number and (b)
the variety of instances mentioned in the premises, that is, the number and diversity of the
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