Unit 7 Deductive Arguments PDF

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the focus in this unit is deductive arguments, we introduce two types of arguments or kinds of reasoning: deductive and inductive (non-deductive) arguments....

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6/28/2021

Unit 7: Deductive Arguments

Unit 7: Deductive Arguments Unit 7: Deductive Arguments: Identification and Evaluation

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Faculty of Humanities & Social Sciences

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PHIL 152: Basics in Critical Thinking, Reading, and Writing (Rev. C7)

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Unit 7: Deductive Arguments

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Joanna Luca

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Monday, 28 June 2021, 8:59 AM EDT

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Table of contents Unit Objectives & Introduction Deductive and Inductive Arguments Evaluating the Relationship between Premises and Conclusions Relevance in a Broader Scope Identifying Irrelevant Details Three Common Types of Deductive Arguments Conditional Statement-based Arguments Disjunctive Argument Evaluating Deductive Arguments Evaluating Language Source and Bias Summary References

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Study Guide Unit 7: Deductive Arguments

Unit Objectives When you have completed Unit 7, you should be able to 1. describe the difference between deductive and inductive arguments. 2. describe the standards of relevancy, necessity, and sufficiency, and describe what role these standards play in deductive and inductive arguments. 3. identify three common deductive argument types: syllogisms conditional statement-based arguments disjunctive arguments 4. evaluate deductive arguments by the standards: truth/acceptability of the premises validity of inference from premise to conclusion 5. describe the standards of clarity and neutrality, and apply these standards to arguments. 6. evaluate arguments by assessing the source and identifying possible bias/prejudice.

Introduction In Unit 7, we extend our discussion of arguments. Although the focus in this unit is deductive arguments, we introduce two types of arguments or kinds of reasoning: deductive and inductive (non-deductive) arguments. We also discuss the standards of relevance, necessity, and sufficiency, and how they apply to deductive and inductive arguments. Our examination of deductive arguments involves identifying three common types of deductive arguments and the relevant standards for evaluating deductive arguments, which includes assessing the truth of the premises and the validity of inference from the premises to the conclusion. As part of the assessment of the language of arguments in general, we present the standards of clarity and neutrality. Beyond the content of arguments, we also introduce standards for assessing arguments, such as assessing the source of an argument, and being aware of possible bias and prejudice that may cast a negative light on what is being said. These last two considerations, evaluation of language and an assessment of the source of an argument, can apply to both deductive and inductive arguments. However, we will leave a more detailed examination of inductive arguments for Unit 8.

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Study Guide Unit 7: Deductive Arguments

Deductive and Inductive Arguments Learning Activity 7.1 Watch the following video: “Deductive and Inductive Arguments.”

Episode 1.3: Deductive and Inductive Arguments

Center for Innovation in Legal Education School of Business, University of Utah

It is essential to distinguish between two types of reasoning or categories of arguments: deductive and inductive. The distinction is based on the concept that some types of arguments can establish the truth of their conclusions beyond the shadow of a doubt, whereas other types can only make it more or less reasonable to accept the conclusion. Example (1), below, is a deductive argument, while example (2) is an inductive argument. 1. Either I’ll cycle or I’ll take the bus. I cannot cycle. Therefore, I will take the bus. 2. I have eaten at Porky’s Rib Joint on three different occasions and the food was excellent. Therefore, it is likely that then next time I go to Porky’s, the food will be excellent. https://gsa.lms.athabascau.ca/mod/book/tool/print/index.php?id=11824

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An important difference between deductive and inductive arguments is that a good deductive argument conclusively proves its conclusion; whereas, even if an inductive argument is as good as it can be, the conclusion is still only likely and can may even turn out to be false. In the first example, if both premises are true, the conclusion must be true; that is, it follows that “I will take the bus.” If you really only have two options (cycling or taking the bus), and you cannot cycle (perhaps your tires are flat and cannot be repaired), the only option left is to take the bus. This line of reasoning is similar to the example in the video. There are two options (eating at the Red Iguana or Café Trang), and one of the options is unavailable or has been eliminated (Café Trang is closed but the Red Iguana is still open); therefore, logically, we must choose the available option (eating at the Red Iguana). In a deductive argument, there is a special relationship between the premises and conclusion by virtue of its structure, such that “if” the premises are true, the conclusion must necessarily be true or follow. Later on in the unit, we will examine three common categories of deductive arguments with unique structures or forms. In the second example, the premise only provides a degree of support for the conclusion. Even if the food was excellent on all three of my previous visits to the restaurant, it could turn out that, the next time I visit the restaurant, the food is horrible. Perhaps, for example, the chef is sick the next time I dine there and her assistants do a poor job with the food preparation. This is also a clear case of a conclusion that goes beyond the evidence in the premises. Here we are basing our conclusion, which is a prediction about the future, on past experiences that can only provide a level of support (remember, we discussed predictions as possible premises whose veracity we could not, in principle, determine with certainty because of timing). The strength of the reasons in support of the conclusion will determine the validity of the deductive argument and whether we are warranted in accepting the conclusion. The best that we can hope for in an inductive argument is that the premises provide strong support for our conclusion.

This discussion of the second example has been adapted from AU's PHIL 252 (Study Guide II, Unit 6, p. 10).

The definitions of deductive and inductive arguments given by many logicians state that deductive arguments are those that purport to establish the truth of their conclusions conclusively; whereas inductive arguments are those that purport to offer good, but not conclusive, reasons for believing their conclusions. It is important to understand the word “purport” in these definitions and why its inclusion is important. This term signifies that the argument, or strictly speaking, the person who gives the argument, is claiming that her argument establishes her conclusion either conclusively or with greater or lesser likelihood. The reason we include this word in our definitions is because, if we simply said that deductive arguments establish their conclusions conclusively, we would not allow for the existence of unsuccessful deductive arguments: those that claim or purport to establish their conclusions conclusively, but fail to do so. Similarly, if we define inductive

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arguments as those that give good reason to believe their conclusions, we would not allow for the existence of unsuccessful inductive arguments: those that claim or purport to give better reason for believing their conclusions than they do in fact give.

Log Entry 32: Deductive Arguments Drawing from the video and the commentary, provide a definition of a deductive argument that allows for distinguishing unsuccessful deductive arguments from successful deductive arguments. Provide an example of each. Click on this link to access Assignment 1

Log Entry 33: Inductive Arguments Drawing from the video and the commentary, provide a definition of an inductive argument that allows for distinguishing unsuccessful inductive arguments from successful inductive arguments. Provide an example of each. Click on this link to access Assignment 1

We will return to these entries when we discuss the three common categories of deductive arguments and the four different kinds of inductive arguments.

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Study Guide Unit 7: Deductive Arguments

Evaluating the Relationship between Premises and Conclusions Standards of Relevance, Necessity, and Sufficiency Learning Activity 7.2 Watch the following video: “Necessary and Sufficient.”

Episode 4.1 Necessary and Sucient

Center for Innovation in Legal Education School of Business, University of Utah

In this section, we will be examining the standards of relevance, necessity, and sufficiency as they relate to both deductive and inductive arguments. Even if the premises of an argument are true or acceptable, this is not, in itself, enough to warrant accepting the conclusion if the premises bear no logical connection to the conclusion. Premises must not only be true or acceptable, they must also be relevant, which is a standard that applies to all premises. Further, the standards of necessity and sufficiency identify the kind of connection that premises bear in relation to their conclusions. We have seen in our discussion of deductive arguments that, if the premises are true, then the conclusion “necessarily” follows. In other words, there is a necessary connection between the premises and conclusions, if the premises are true. However, premises in inductive arguments can also be necessary, in the https://gsa.lms.athabascau.ca/mod/book/tool/print/index.php?id=11824

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sense that a premise or premises are needed or required to draw the conclusion; that is, you can’t reach the conclusion without them. But, even so, the fact that they are true doesn’t guarantee the truth of the conclusion as in deductive arguments because the premises may not be sufficient or enough to warrant the acceptance of the conclusion. This should not be surprising since the conclusions of inductive arguments go beyond the premises and therefore, even though the premises only provide a degree of support, this is not inconsistent with the requirement that they must be true in order for the conclusion to be true. In Unit 8, we will discuss the standard of sufficiency as it applies to inductive arguments, as well as provide exercises to practice assessing this standard. In this unit, we provide some practice exercises for judging relevance in relation to a topic, main idea, and purpose, which is a broader treatment of relevance than the simple application of judging the relevance of a premise to a conclusion. This is particularly useful because relevant supporting details may be important to the rhetorical modes discussed in Part A of the course.

Log Entry 34: Evaluating the Relationship between Premises and Conclusions Add three subheadings: Relevance, Necessity, and Sufficiency. Drawing on the video and commentary, provide a definition of relevance, necessity, and sufficiency, and explain whether these standards have a role to play in deductive and inductive arguments. If so, explain how they play a role, and explain how you would evaluate an argument by applying the standards that are applicable to each type of argument. Click on this link to access Assignment 1

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Study Guide Unit 7: Deductive Arguments

Relevance in a Broader Scope In the previous section, our focus on the standard of relevance as it applies to arguments was somewhat narrow in scope — it is important to grasp relevance more broadly, including how it might be applied to rhetorical modes, by considering the context of a specific topic, main idea, and purpose. For example: subject: pollution main idea: each of us can do practical things to reduce pollution purpose: persuade and trigger action In a paragraph with the above context, it would be relevant to discuss the use of a compost heap for kitchen garbage. Why? Such a suggestion is a practical pointer that readers can put into action. It is not only related to the subject matter at hand, it is directly to the point of the main idea, and is logically related to the purpose. In effect, it is an example of a practical thing that we can do to reduce pollution, and hence provides support for the main idea. It would be irrelevant to list, in the same paragraph, the types of harmful chemicals found in fish taken from the Great Lakes, even though this point is related to the subject of pollution. Since it does not tell the reader what he or she can do to reduce pollution, it is not related to the main idea. Although such a list might induce some readers to write letters to the government or to become more concerned about the issue of pollution, for many others it may only add to their fears and to a feeling of helplessness in the face of an enormous and complex problem. Thus, it is unlikely to further the purpose of the paragraph. Now, suppose that the writer has included the following points in the same paragraph. Identify those you consider irrelevant, and then read the discussion of each of these points. 1. plastic shopping bags can be reused 2. bottled water may contain as many harmful chemicals as tap water 3. baking soda and vinegar are good all-purpose cleaners 4. walking is an excellent form of exercise 5. governments at all levels should support more recycling efforts 1. This point is relevant since, like the compost heap suggestion, it identifies a concrete and practical action that can be taken immediately and easily. 2. As with the list of harmful chemicals found in fish, this point is likely to cause fear and frustration without offering the reader any advice on what can be done about the problem. It is, therefore, irrelevant.

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3. Baking soda and vinegar are familiar and accessible products. Once again, this is a relevant point since it suggests a direct action. 4. This point is irrelevant as it appears on the list; however, the suggestion that walking is often a practical alternative means of travel as opposed to automobiles, which contribute to pollution, is relevant. As further incentive for action, the writer might wish to state the benefits of walking as a form of exercise. The point could be relevant in such an expanded form because it would increase the likelihood that the purpose will be met. Further, this suggests that determining whether something is relevant or irrelevant also depends on whether the connection or support between a supporting detail and main point is partially implicit. 5. This point may be true and heartfelt, but it is not immediately relevant. The main idea specifies actions for people as individuals. Mention of “governments at all levels” immediately places the problem and any solutions to it at a distance, and may only add to a reader’s sense of helplessness. After all, what can one person do about such a huge problem? As with point 2 and the Great Lakes example used earlier, this point may actually run counter to the writer’s purpose. Unless the writer goes on to suggest real and practical actions that a reader is immediately capable of performing to provoke such government support, the point is irrelevant.

Note that judging relevance in a broader scope is not as straightforward a matter as it may be when assessing a simple argument in which the matter at hand is to determine the relevance of premises to conclusions. When applied more broadly, the subject matter, main idea, and purpose must also be taken into consideration.

Exercise 7.1: Identifying Relevant Support Click on this link to complete Exercise 7.1

When writing to persuade, or when reading a passage written for that purpose, be especially alert to the problem of using irrelevant truths. Note the main idea of the passage, and ask yourself whether the point is relevant in the overall context of purpose, topic, and main idea. Suppose you are reading a magazine column that suggests cell phones are a driving hazard and their use should be banned in moving vehicles. The writer states it is ludicrous that the average person feels he or she must be available by phone every moment of every day. We can view the author’s criticism of the claim that people have to be available by phone all the time in two different ways. We could see this observation as heartfelt, but irrelevant in this context because it does not directly address the question of whether cell phone use in a moving vehicle constitutes a driving hazard. Instead, this claim is making a general value judgment about the “overuse” of cell phones in this society. On the other hand, this criticism might be relevant if the author supposes that we could allow cell phone use, assuming the benefits outweigh the danger. In this case, the author would be arguing that the apparent costs of not being able to talk on the phone while driving arises from a misconception that we should be always be

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available. If we were to accept the latter interpretation, it would be based on a partially implicit connection between the supporting detail and the main point. Deciding which interpretation is the most reasonable would depend on the topic, main point, and purpose of the passage. Take a moment to reread Log Entry 31, which contains the definition of relevance. Keep this definition in mind as we move from this general discussion to examine a variety of specific cases.

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Study Guide Unit 7: Deductive Arguments

Identifying Irrelevant Details An important part of the critical examination of reading passages is to note whether the writer has remained on track and has included only relevant ideas. A loose and rambling style that drifts from thought to thought may be appropriate for personal journals or perhaps as a stylistic choice in some fiction, but we expect to find coherence and unity in most of our reading material. As an active and alert reader, you will find it useful to formulate statements of subject, main idea, and purpose to test your understanding of the material. Then, use these statements as guidelines in judging the relevance of what the author has chosen to include. For the passage below, make brief marginal notes concerning subject, main idea, and purpose. Skim the passage, identify any sentences you think are irrelevant, and identify why you think they are irrelevant.