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Chapter 25: Analogies. Uses of Analogy (pp. 252-255) Analogies are based upon comparisons between two or more objects. Arguments by analogy do not result.

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Presentation on theme: "Chapter 25: Analogies. Uses of Analogy (pp. 252-255) Analogies are based upon comparisons between two or more objects. Arguments by analogy do not result."— Presentation transcript:

1 Chapter 25: Analogies

2 Uses of Analogy (pp ) Analogies are based upon comparisons between two or more objects. Arguments by analogy do not result in a general conclusion. Analogies are used to describe. –Similes When you make a direct comparison between two or more objects and you say one is like another, or that you should understand one thing as a thing of a different kind, you have a simile. Example: “Some people would have said that Peter was aimless. I knew better. He was like a sail, something that’s slack only until it captures the wind. And then it possesses the force of the wind.” (Robert Ludlum, The Sigma Protocol [New York: St. Martin’s Press, 2001], p. 175)

3 Uses of Analogy (pp ) –Metaphors Metaphors are like similes except there is no direct comparison. One claims that some thing is a thing of a different kind. Example: “John was a beast.” Analogies are used to explain. –Explaining how If you were puzzled by a math problem, someone might explain how to do it by comparing it to a problem you were able to do. –Explaining why When Anne Frank explained why the cats had the names they did, she made a comparison between the behavioral characteristics of the cats and the behavioral characteristics of the Germans and the English. (For the passage, see p. 34.)

4 Uses of Analogy (pp ) Analogies are used to inquire. –About 80 years ago, Ludwig Wittgenstein claimed that language is a picture of the world. His metaphor provided the basis for extensive enquiry. The inquiry consisted of unpacking the metaphor: showing the specific points of similarity. Analogies are used to argue. –Strengthening and weakening analogical arguments –Relevant similarities and differences

5 Evaluating Arguments by Analogy (pp ) Parts of an argument by analogy –Ground for the analogy The ground consists of those objects having all the properties under consideration. –Objective extension of the analogy The objective extension of an analogy that is compared to the ground and known to have a number of properties in common with the ground. –Basis of an analogy The basis of an analogy consists of those properties known to be common to the ground and the objective extension of the analogy. –Problematic extension of the analogy The problematic extension of an analogy is the property common to the objects in the ground but not known to be a property of the objective extension.

6 Evaluating Arguments by Analogy (pp ) Criteria for evaluating arguments by analogy –1. The more respects in which things being compared are similar (the larger the basis), the stronger the argument is.

7 Evaluating Arguments by Analogy (pp ) –2. The respects in which things are compared (the properties included in the basis) must be relevant to the conclusion. –3. The analogy is stronger if more things are compared (if the ground of the analogy is larger).

8 Evaluating Arguments by Analogy (pp ) –4. Relevant differences between things compared (the ground and the objective extension) tend to weaken the analogy. The differences have to be relevant. If you’re comparing cars or computers, the color of the body or case is irrelevant to performance. In some cases, for example, the behavior of insects, you might not know precisely what is relevant. In the case of insect behavior, the color of the insects might be relevant.

9 Evaluating Arguments by Analogy (pp ) –5. When a significant number of things are similar in a significant number of respects (when the ground and the basis are strong), differences among objects in the ground can strengthen the evidence for the conclusion of the analogy. If you’re concerned with the reliability of a certain make and model of computer, and you’ve known a goodly number of people who use and abuse their computers of that make and model in numerous ways but it remained reliable, you have good reason to believe it is reliable regardless of the behavior of its users.

10 Evaluating Arguments by Analogy (pp ) –The stronger the conclusion is relative to the premises, the weaker the argument is. The strength of the conclusion is determined by the difficulty involved in falsifying it. If you have a universal statement, for example, it takes only one counterexample to falsify it.

11 Evaluating Arguments by Analogy (pp ) Differences between inductive and valid deductive arguments –The conclusion of a valid deductive argument follows, period. –Inductive arguments are strong or weak to some degree. –Additional premises often can strengthen or weaken an inductive argument. Look for unstated respects in which things are (or are not) similar.

12 Example of Analyzing an Argument by Analogy You’re deciding whether to attend a recent movie, Gangs of New York. It’s directed by Robert Altman, and you’ve enjoyed his earlier pictures. It stars Leonardo DiCaprio, and you liked his performance in Titanic and Catch Me If You Can. The topic is gang violence in New York City, and you enjoyed West Side Story and The Godfather. So, decide to attend the move, expecting to enjoy it. –1-2. Respects of similarity and their relevance: You can expect Altman movies to be similar in style, since directors develop individual styles. Similar, actors tend to develop a style and a certain quality of acting. So, there are similarities that seem to be relevant.

13 Example of Analyzing an Argument by Analogy –3. If you’ve seen a dozen Altman films and enjoyed them all, that’s a significant number. If you have seen only two DiCaprio films, that’s not a significant number, but that might make little difference. –4. There are relevant differences between Gangs of New York, and West Side Story and The Godfather. West Side Story is a musical. The Godfather concerns organized crime, rather than street gangs. So, the fact that you enjoyed those movies is probably irrelevant to the enjoyableness of Gangs of New York. –5. Since Altman films have covered numerous topics, and since DiCaprio films have been on various topics, the fact that you enjoyed them all tends to strengthen the argument.

14 Example of Analyzing an Argument by Analogy –6. Your conclusion is fairly weak. You expect to enjoy the movie, although you don’t suggest it will be anything like the best movie you’ve seen. So, the last criterion tends to suggest that the argument is probably strong. Should you go to the movie? Probably. You have reason to believe that it will be a movie you’ll enjoy.

15 Example of Analyzing an Argument by Analogy There is one more point that probably should be noted. If you attend Gangs of New York and you don’t like it, it will not be a major loss. So, when determining whether or not to attend a particular movie, you might not engage in an elaborate analogy. Or you might take a single element as a reason not to attend. If you’re looking at a major purchase or a medical procedure, on the other hand, the points of similarity and difference become more pressing. In the latter cases, you might well want to find a significant number of respects in which you are similar to others and a significant number of users or patients.


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