In Defense of Informal Logic

Part of the Argumentation Library book series (ARGA, volume 2)


I want to defend informal logic. Unlike the philosophers quoted above, I do not compare it unfavorably with formal logic. For them the comparison is unfavorable because, by contrast with informal logic, formal logic does have a theory. This theory defines an ‘argument’, and by reducing questions about argument correctness to questions about argument form, it provides a model of argument correctness. However, formal logic can boast about having such a theory only by not being overly concerned with practice. Not only is the theory illustrated and supported by contrived examples, but applications of it to arguments in their natural habitat are cited almost as an after-thought, as though the theory does not really depend on the existence of these applications. I side with informal logic even if it does not have a theory because it is about arguments in actual discourse. Moreover, I’m not sure why any theory is needed to appreciate the practical value of informal logic in providing resources for critical thinking.


Complete Form Logical Theory Valid Argument Declarative Sentence Informal Logic 
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  1. 1.
    Finocchiaro’s paper is criticized in Trudy Govier, “Four Reasons There are No Fallacies,” (1987, pp. 177–201), which I did not read until after my paper was published. Her paper also discusses the arguments by Lambert and Ulrich (1980) and Gerald Massey (1981) that are discussed or quoted in this essay. Govier’s paper is especially useful for its exposure of the deductivist prejudices in these writings. Govier wants to defend informal logic against the charge that it has no adequate theory, whereas I want to question the idea that it needs one. This explains why we find very different things to talk about in connection with the authors we criticize.Google Scholar
  2. 2.
    The requirement that an argument be complete is clarified and explained in the fourth section of the sixth essay of this book, “The Case of the Missing Premise,” where it is referred to as the ‘PC Requirement’.Google Scholar
  3. 3.
    As Latta puts it, “A common jaywalker charged with jaywalking any place in the United States is entitled to know when and where the alleged offence is supposed to have occurred. Is the President entitled to less?” (Fields 1978, pp. 256–7).Google Scholar
  4. 4.
    Quoted in Fields (1978, p. 257). The official transcript deletes this part of his speech. See “Debate on Articles of Impeachment,” Hearings of the Committee on the Judiciary, House of Representatives Ninety-Third Congress (1974). Google Scholar
  5. 5.
    When Trudy Govier (1983) tries to formulate the relevance condition for an ad hominem attack on 1, she emphasizes the importance of considering whether the arguer has any basis for judgement or any independent evidence for the things 1 is saying, i.e., whether the arguer is “epistemically dependent” on J. If the arguer is epistemically dependent on J, and the character defect the arguer is imputing to J does bear either on 1’s sincerity or the likelihood that J has used good judgement in assessing the relevant evidence bearing on the claim that he or she has made, the ad hominem argument may not be fallacious. Govier’s real concern is to undermine the deductivist presumption that what is wrong with ad hominem rhetoric is that the premises do not logically entail the conclusion, a presumption which is responsible for ignoring the fact that sometimes ad hominem reasoning can be non-fallacious. However, her interest in specifying the conditions under which an ad hominem argument is fallacious does suggest that she, too, is assuming that informal logic is supposed to offer tests of argument correctness.Google Scholar
  6. 6.
    Gerald Massey also is assuming that there should be such definitive criteria when he says, in the quote at the top of this paper, that there is no theory of fallacy whatsoever. His reasoning is that a fallacy is an invalid argument, and “there is no method whatsoever of establishing invalidity (i.e., that an argument has an invalid argument form) that has theoretical legitimacy” (1981, p. 494). Although Woods and Walton (1977) disagree with Massey that a theory cannot be developed, they do agree with him that it is needed. “An informal fallacy is… an invalid argument, and where the invalidity of argument is concerned, some clearly articulated decision mechanism, some theoretically adequate model, should be looked for” (p. I).Google Scholar
  7. 7.
    That everything relevant to the assessment of an argument be incorporated in the lay out of the argument as a premises-conclusion sequence is much too vague and general a requirement, as Trudy Govier pointed out when she served as an Informal Logic referee for the sixth essay in this collection. (Anthony Blair, in correspondence with me concerning that same essay, also effectively criticized this version of the requirement.) According to logical theory, that an argument has a valid argument form is certainly relevant to its assessment, but the fact that it has the form or that the form is valid is not to be included as a premise of the argument. Rather than make the requirement less vague or general here, where nothing much turns on how it is formulated, I improve on the statement of the requirement in the sixth essay in this collection, which addresses the problem of the enthymeme.Google Scholar
  8. 8.
    The term is borrowed from Frank Ebersole (1967, p. 103).Google Scholar
  9. 9.
    The concluding section of essay three (on the ad baculum) takes up the question of what we are doing when we label or refer to a fallacy in an argument, by contrast with the present discussion which focuses on the question of what a fallacy is. The de re focus of the present essay is a function of the fact that it is concerned with what a fallacy is, according to logical theory.Google Scholar
  10. 10.
    Finocchiaro maintains that an incorrect argument resembles one that is correct in only three ways: it claims to be deductively valid when it is deductively invalid; it claims to be inductively strong when it is inductively weak; it claims to have some inductive strength when it has none. Since an argument in its natural habitat does not make any claims about being deductive or inductive, his scheme is difficult to apply. Moreover, the scheme assumes that what is being classified are arguments in complete form. LU’s fallacious assumption that any rhetoric may be represented as an argument does not seem to fit in the scheme, and neither does their assumption that informal logic must provide tests of argument correctness. Indeed, the scheme is based on a fallacious assumption that also does not fit in the scheme, namely, that informal logic must make sense in terms of (formal) logical theory.Google Scholar
  11. 11.
    What is at issue in defining `argument’ is discussed in much more detail in the fifth essay of this collection.Google Scholar

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© Springer Science+Business Media Dordrecht 2000

Authors and Affiliations

  1. 1.University of OregonEugeneUSA

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