1. 9.1 Analogical Reasoning
Analogical reasoning may be understood as a subtype of inductive reasoning.

2. 9.1 Analogical Reasoning
Analogical reasoning depends on a comparison of instances.
The process involves citing accepted similarities between different domains to support the conclusion that some further similarity exists between them.

3. 9.1 Analogical Reasoning General form:
P1) Entity A has attributes a, b, c, and z.
P2) Entity B has attributes a, b, c.
C) Therefore, entity B probably has attribute z as well.

4. 9.1 Analogical Reasoning General form:
P1) Entity A has attributes a, b, c, and z.
P2) Entity B has attributes a, b, c.
C) Therefore, entity B probably has attribute z as well.
NOTE: You can see how this reasoning could be given a deductive structure.

5. 9.1 Analogical Reasoning P1) Entity A has attributes a, b, c, and z.
P2) Entity B has attributes a, b, c.
P3) If two entities share attributes a, b, and c, then they will also share attribute z.
C) Therefore, entity B has attribute z.
The above argument is a valid deductive argument, but the cases where it is sound are not cases where the argument is particularly informative.

6. 9.1 Analogical Reasoning P1) Entity A has attributes a, b, c, and z.
P2) Entity B has attributes a, b, c.
P3) If two entities share attributes a, b, and c, then they will also share attribute z.
C) Therefore, entity B has attribute z.
The above argument is a valid deductive argument, but the cases where it is sound are not cases where the argument is particularly informative.
Stronger examples can be given in the case of legal reasoning, which we get to next time. Note the additional premise is a generalized claim.

7. 9.1 Continued
Analogical arguments are closely related to generalizations. In a generalization, the arguer begins with one or more instances and proceeds to draw conclusions about all members of the class.
In pure analogical arguments, we skip the generalization step and try to learn about one case by appealing to others directly – an inductive process.

8. 9.1 Continued
When we use analogical reasoning, the entities being compared with one another are called analogues.

9. 9.1 Continued
Primary vs. Secondary Analogues The primary analogue serves as a standard of comparison for the secondary analogue.

10. 9.1 Continued Primary vs. Secondary Analogues
Argument: Christopher Nolan’s latest movie is probably good, because his previous two movies were good.
The two earlier movies are the primary analogues
The latest movie is the secondary analogue

11. 9.1 Principles for Evaluating Arguments from Analogy
Example:
You wake up one morning to learn that the Society of Music Lovers hooked you up to a famous violinist, so that your kidneys will extract poisons from his blood. The decision was made by the Society: he is injured and unconscious, and if you unhook yourself from him, he will die. After nine months, he will recover from his ailment and they will unplug him from you.

12. 9.1 Principles for Evaluating Arguments from Analogy
Example:
You wake up one morning to learn that the Society of Music Lovers hooked you up to a famous violinist, so that your kidneys will extract poisons from his blood. The decision was made by the Society: he is injured and unconscious, and if you unhook yourself from him, he will die. After nine months, he will recover from his ailment and they will unplug him from you.
Intuitively, you are not morally obligated to remain hooked to the violinist; it is morally permissible to unplug him, even though it would result in his death. (It might be nice of you to continually filter his bloodstream, but you are not obligated.)

13. 9.1 Principles for Evaluating Arguments from Analogy
P1) In the violinist case, a human is (blamelessly) dependent on the use of your body to survive for nine months, in an arrangement that came about against your will. Intuitively, it is not the case that you are morally obligated to remain hooked to the violinist: you may unplug him.

14. 9.1 Principles for Evaluating Arguments from Analogy
P1) In the violinist case, a human is (blamelessly) dependent on the use of your body to survive for nine months, in an arrangement that came about against your will. Intuitively, it is not the case that you are morally obligated to remain hooked to the violinist: you may unplug him. [VIOLINIST SCENARIO = PRIMARY ANALOGUE]

15. 9.1 Principles for Evaluating Arguments from Analogy
P1) In the violinist case, a human is (blamelessly) dependent on the use of your body to survive for nine months, in an arrangement that came about against your will. Intuitively, it is not the case that you are morally obligated to remain hooked to the violinist: you may unplug him. P2) In cases of pregnancy by rape, a human is (blamelessly) dependent on the use of your body to survive for nine months, in an arrangement that came into being against your will. .

16. 9.1 Principles for Evaluating Arguments from Analogy
P1) In the violinist case, a human is (blamelessly) dependent on the use of your body to survive for nine months, in an arrangement that came about against your will. Intuitively, it is not the case that you are morally obligated to remain hooked to the violinist: you may unplug him. P2) In cases of pregnancy by rape, a human is (blamelessly) dependent on the use of your body to survive for nine months, in an arrangement that came into being against your will. . [CASES OF PREGNANCY BY RAPE = SECONDARY ANALOGUE]

17. 9.1 Principles for Evaluating Arguments from Analogy
P1) In the violinist case, a human is (blamelessly) dependent on the use of your body to survive for nine months, in an arrangement that came about against your will. Intuitively, it is not the case that you are morally obligated to remain hooked to the violinist: you may unplug him. P2) In cases of pregnancy by rape, a human is (blamelessly) dependent on the use of your body to survive for nine months, in an arrangement that came into being against your will. . C) Analogously, it seems likely that in cases of pregnancy by rape, it is also the case that you aren’t morally obligated to remain pregnant, and may abort the fetus.

18. 9.1 How do we evaluate arguments from analogy?
The more relevant the similarities between primary and secondary analogues, the stronger the argument.
For example, in the preceding argument, the strength of the argument is partially dependent on how relevant the lack of consent is to whether or not there is a moral obligation.

19. 9.1 How do we evaluate arguments from analogy?
The greater the number of similarities between primary and secondary analogues, the stronger the argument.
If there are lots of (relevant) similarities between the two cases, we are more likely to accept the inference to the conclusion.

20. 9.1 How do we evaluate arguments from analogy?
Differences between primary and secondary analogues are disanalogies.
Disanalogies, generally speaking, weaken arguments from analogy…
For example, a potential disanalogy in the violinist/pregnancy case would be if there were some sort of special relationship that exists between pregnant mothers and fetuses.

21. 9.1 Continued
The greater the number of similar primary analogues, the stronger the argument.
For example, we could strengthen the violinist/pregnancy argument by adding in more cases where a human’s life depends on another’s without that other’s consent, for reasons that the dependent human isn’t at fault, and where we additionally judge that there is no moral obligation to keep them alive.
Increasing the number of primary analogues reduces the likelihood that the properties only sometimes appear together accidentally.

22. 9.1 Continued
Dissimilar primary analogues are counteranalogies, which weaken the argument.

23. 9.1 Continued
The more diverse the primary analogues, the stronger the argument.
Variation among primary analogues suggests that whatever property is shared is not some fluke.

24. 9.1 Continued
The more specific the conclusion, the weaker the argument.
Highly specific conclusions are easy to falsify!

25. 9.1 Continued CAREFUL Two mistakes we can make regarding analogies:
Using faulty analogies to make points
Analogical literalism

26. 9.1 Continued
Faulty or false analogies draw a conclusion based on cases that are not actually analogous to one another – they are not, in other words, similar in such a way that we should infer they share the additional property.
But the presence of any difference between cases does not mean there’s a faulty analogy!

27. 9.1 Continued
Rejecting an analogical argument on such grounds is falling prey to the fallacy of analogical literalism.
Example: “We’re wrong to conclude that abortion is morally permissible in cases of rape, because fetuses can’t play the violin.”
The reasoning on which the decision for both cases turn has nothing to do with violin- playing.

28. Try It In the next 10 minutes, develop:
An argument from analogy for a particular political/legal conclusion
An argument from analogy for a particular ethical/moral conclusion
(We’ll learn more about moral and legal reasoning next class – for now just draw on what you’ve learned about analogical reasoning.)