Informal Logic

Informal Logic: Issues and Techniques

Copyright Date: 1997
Pages: 280
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  • Book Info
    Informal Logic
    Book Description:

    Grennan bases his evaluation of arguments on two criteria: logical adequacy and pragmatic adequacy. He asserts that the common formal logic systems, while logically sound, are not very useful for evaluating everyday inferences, which are almost all deductively invalid as stated. Turning to informal logic, he points out that while more recent informal logic and critical thinking texts are superior in that their authors recognize the need to evaluate everyday arguments inductively, they typically cover only inductive fallacies, ignoring the inductively sound patterns frequently used in successful persuasion. To redress these problems, Grennan introduces a variety of additional inductive patterns.

    eISBN: 978-0-7735-6645-3
    Subjects: Philosophy

Table of Contents

  1. Front Matter
    (pp. i-iv)
  2. Table of Contents
    (pp. v-xii)
  3. Preface
    (pp. xiii-2)
  4. 1 Arguments
    (pp. 3-15)

    This book will present a procedure for evaluating arguments conceived as the products of utterances that are themselves best regarded as speech act complexes. As products of utterances they are sets of propositions produced byS,the utterer, with the intention of persuading someone,H,that s/he ought to believe one part of the set (the conclusion) because of the remainder of the set, the premisses.¹ (I am discussing arguments with only one inference step in this chapter.)

    The recipient of an argument,H,who wishes to evaluate it, must answer, at the most general level, one question:

    (1a) To...

  5. 2 Current Argument-Evaluation Techniques
    (pp. 16-33)

    The presentation of another argument-evaluation procedure is defensible only to the extent that the extant ones are deficient. In this chapter I want to describe and critique the more popular approaches to argument evaluation found in the textbooks designed for undergraduate courses offered by philosophy departments in American and Canadian universities. They will be examined in terms of how well they equip anyone who masters their techniques for the evaluation of everyday argumentation.

    Two distinct approaches are now common. The first one I will discuss can be called the “traditional approach,” but of course this is a tendentious label, suggesting...

  6. 3 An Argument-Evaluation System
    (pp. 34-63)

    In the last chapter a number of deficiencies were identified in texts of both the traditional and informal logic types. Although the latter type must be considered a vast improvement in usefulness for evaluating everyday argument, there were deficiencies noted that could be summarized in the complaint that the informal logic texts are unnecessarily informal.

    I believe that the informal logic approach can be more systematic in arriving at judgments about argument quality, more precise in stating these judgments, and if I am right about this, more accurate in its appraisals.

    An adequate argument-evaluation procedure must be based on two...

  7. 4 Diagramming Arguments
    (pp. 64-92)

    The system of argument evaluation presented in this work relies on depicting the structure of arguments in diagrammatic form. However, in the broader context of argumentation studies the value of diagrammatic representations of arguments has been questioned. Charles Willard has raised a number of objections which, in the end, seem to amount to the complaint that no diagram can “serve as a structural representation of human cognitive processes given the complexity of those processes” (1976, 311). From the perspective of the two types of diagrams to be examined here, Willard has constructed a straw man. These diagrams do not aspire...

  8. 5 Evaluation of Deductive Inference
    (pp. 93-127)

    In this chapter I will assess the strengths and weaknesses of currently available techniques for testing inferences for deductive validity, both formal and material, including some techniques that have not been given the attention they deserve.

    In the area of inference-evaluation technique, modern-day logicians have devoted almost all their attention to developing logical systems that can be used to test inferences for deductive validity arising from logical form. When an argument is formally valid the warrant supporting its inference claim is a formal tautology. I will examine techniques that have been developed for evaluating arguments involving prepositional reasoning and for...

  9. 6 Inductive Inference Evaluation
    (pp. 128-150)

    The strategies discussed in the last chapter were developed to identify deductively valid inferences, either ones that are formally valid by virtue of having formal tautologies as warrants or ones that are materially valid by virtue of having necessarily true warrants. Any argument that is found to be deductively valid in either of these ways can be given the highest possible inference rating. But how are we to deal with ones that are found not to be deductively valid?

    A “deductive chauvinist” would have no difficulty with this question: we should regard the arguments as logically worthless, ignore them! But...

  10. 7 An Inductive Argument Typology
    (pp. 151-219)

    In the previous chapter I introduced the rebuttal-factor approach for evaluating the inferences of inductive arguments. Prior to that I discussed the warrant-backing method, which requires us to judgep(C/P)after reviewing the warrant backing that is relevant to the inference. Neither of these approaches by itself provides specific strategies for inference evaluation, but of course, since we are dealing with arguments whose warrants are dependent on argument content itself, we cannot expect the procedures to be both specific and universal.

    Specific advice for inference evaluation must be given in terms of particular inductive argument patterns, if it is to...

  11. 8 Premiss Evaluation
    (pp. 220-250)

    The third step of the recommended argument evaluation procedure is the evaluation of the individual uninferred premisses. The outcome of this step is a rating for each premiss, assigned either directly or by selecting a verbal equivalent from the premiss-rating table (Table 3) given in chapter 3.

    At the most general level there are three strategies that might be considered suitable. First, and least satisfactory, is to ask, What supporting information does one have forP? or What reasons does one have for acceptingPas true? This approach is apt to result in the assignment of a rating that...

  12. 9 Missing Premisses
    (pp. 251-274)

    Arguments depend not only on their premisses to persuadeHthatCis acceptable. Every argument, if it is to be satisfactory, requires also thatHagree withSon a variety of other implicit assumptions. Some logicians regard some of these assumptions as missing premisses, and if they are correct, their position has repercussions for argument evaluation theory: “Anyone who has tried to evaluate natural arguments will know that these missing premisses ... must be formulated, for the strength or weakness of the argument very often depends on what they are” (Blair and Johnson 1980, 18).

    The most fundamental...

  13. 10 Conclusion
    (pp. 275-284)

    Since the goal of this book has been to present a system, including strategies, for argument evaluation, it is not possible to state some particular thesis that I regard as having been proved. It is more appropriate to provide a brief outline of the system developed and to indicate how the various chapters are relevant to different aspects of it. And since I conceive of the essay as a work in informal logic, it seems appropriate to indicate the problems that it addresses within the subject.

    This book presents a formal procedure for argument evaluation, intended to enable argument “consumers”...

  14. Notes
    (pp. 285-296)
  15. Bibliography
    (pp. 297-304)
  16. Index
    (pp. 305-309)