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Logical Fallacies: Formal and Informal Fallacies

Abstract: The nature of fallacies is examined. Informal and formal fallacies are characterized in an introductory manner. The traditional treatment of fallacy is disorganized and the general nature of an informal fallacy is not well understood.

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  1. The historical standard treatment of fallacies, still used in many introductory university logic courses, has serious difficulties.

    1. C.L. Hamblin points out that after 2,000 years the standard treatment of fallacies remains much the same as the thirteen fallacies pointed out by Aristotle in his Sophistical Refutations. He decries the standard treatment:
      “[I]n most cases, I think it should be admitted, is as debased, worn-out and as dogmatic a treatment as could be imagined — incredibly tradition-bound, yet lacking in logic and historical sense alike, and almost without connection to anything else in modern logic at all.”[1]
      And Douglas Walton cautions:
      “Very often so-called informal fallacies turn out not so much to be arguments that are wildly wrong as to be important types of attacks, objections, replies, criticisms or refutations that occur in familiar argumentation in science, law, politics, and all aspects of life and learning.”[2]
      Currently, defeasible reasoning and informal fallacies are analyzed in accordance with argumentation schemes and pragmatic theories of dialogic. Occasionally, “traditional informal fallacies” can be set out and explained as acceptable arguments.[3]

      1. Some logicians, e.g., Francis Bacon[4] and John Locke,[5] did not assay the treatment of informal fallacies because they emphasized that logic is concerned with correct reasoning.

      2. Yet, unless we are aware of some of the mistakes that are likely to be made, i.e., unless we know how to avoid typical mistakes in thinking, we are unlikely reason well.

    2. No one is particularly satisfied with the traditional treatments of fallacies — many cannot be categorically well-defined. Thus, it may well be impossible to give a systematic treatment of fallacies, in part because different methods of logic have been adopted and in part because the nature of errors in reasoning are not always due to grammar and forms of language.[6]

      1. Augustus De Morgan writes in his Formal Logic: “There is no such thing as classification of the ways men arrive at an error: it is much to be doubted whether there ever can be.”[7]

      2. H.W.B. Joseph says in his Introduction to Logic, “Truth may have its norm, but error is infinite in its aberrations, and they cannot be digested in any classification. The same inconclusive argument may often be referred at will to this or that head of fallacies.”[8]

        E.g. in syllogistic logic the four term fallacy is described as a formal fallacy but when the same argument is identified as the fallacy of equivocation, an informal fallacy is said to result.

      3. No unified theory of fallacy has been proposed, except in an exceedingly superficial manner by negative definition. I.e., a fallacy is said to be incorrect reasoning. This negative definition is, of course, dependent upon having a complete and consistent explication of the meaning of proper reasoning.

      4. Most likely, however, what we call ‘fallacy’ has no common single meaning, and the characterization of the uses of this word conform to Ludwig Wittgenstein's notion of “family resemblance” where “we see a complicated network of similarities overlapping and criss-crossing; sometimes overall similarities, sometimes similarities of detail.”[9]

  2. Even though there exists no agreed upon theory of fallacy, informal fallacies in this course will be more or less organized traditionally. An attempt is made to incorporate the standard treatment of fallacies with a view toward informed practicality in everyday reasoning.

    1. First, what is a fallacy? In general, it is some form of deceptive reasoning.

      1. A traditional view of fallacy, then, is an “argument which seems to be valid, but really is not.”[10] However, several serious problems with this definition are evident.

        1. The definition is psychological; it turns on whether an individual happens to be misled by an argument. What could count as something being unqualifiedly “deceptive”? E.g. consider this oft-used fallacy of equivocation in several introductory textbooks:

          Whatever is immaterial is unimportant.
          Whatever is spiritual is immaterial.
          Therefore, whatever is spiritual is unimportant.[11]

          Since, few persons would think the argument seems to be valid, on the above definition, the syllogism would not be treated as fallacious because it is not deceptive.

        2. Additionally, the notion of validity is normally applied only to deductive arguments. So the above definition would not address the incorrectness of inductive or probabilistic arguments. Moreover, in the case of petitio principii (circular reasoning), the fallacious aspect is not its deductive invalidity, but instead its deceptiveness. Moreover, many researchers argue that some informal fallacies are not viewed as arguments but instead as deceptive techniques or rule violations. For example, the fallacy of many questions is not prima facie an argument.

      2. Fallacy: a type of mistake in reasoning and argumentation describable in terms of a rule violation of that type of logical scheme in which it occurs..

        This definition is clearly inadequate as well, since it presupposes there is a set of known, agreed-upon rules for all forms of systematic reasoning. Nevertheless, the definition is assumed here as a conventional working definition.[12]

        The framework for various kinds of fallacies depends upon a theory of argument — i.e., what kinds of arguments are rule-based. No matter how logic in general is described, a fallacy can be thought of as a violation of a logical-rule in one or more of its kinds or divisions. As to whether or not, there is only one type of correct logic is a matter of disagreement.[13]

      3. In current practice the notion of fallacy in argumentation is interpreted in several different ways:

        1. In semantical, formal deductive logical theories, “fallacy” is defined in terms of a violation of formal logical rules; for instance, the fallacy of the undistributed middle term occurs in Aristotelian syllogistic logic and the fallacy of affirming the consequent in symbolic or mathematical logic.

        2. In pragmatic argumentation theory, a fallacy is defined as the violation of a normative rule or conversational maxim occurring in a dialogue or critical conversation. For instance, evading the burden of proof in an argument or providing irrelevant arguments both count as incorrect moves in a critical discussion. Presently, several significant accounts of pragmatic dialogical norms or rules have been proposed, and in general in those accounts a fallacy is defined as a violation of the variously determined norms, rules, or procedures.

        3. In other critical reasoning contexts, an informal fallacy is been defined in terms of false premises, statements or presuppositions in an argument as an intentional deception, and even as a shift from one dialogue model to a different one.[14]

    2. Let us classify two basic types of fallacies:

      1. Informal Fallacy: those dependent upon language — i.e., a fallacy that arises from the content of an argument (the what is said), not the logical form or structure of the argument (the how it is said). Informal fallacies usually arise in ordinary language contexts from mistakes in everyday argumentation and persuasion.

        The pragma-dialectical theory (the study of language use in two-party conversations) of fallacy developed by the Amsterdam School (Frans H. van Eemeren and Rob Grootendorst) define fallacies violations of rules for critical discussion.[15] Douglas Walton enumerates six conditions or characteristics for fallacy in the pragmatic theory.[16] Both accounts depend upon an interpretation of multiple conditions with considerable open texture involving judgments without criteria of reasonableness, acceptableness, relevance, and sufficiency.

        Logic and critical reasoning textbooks usually explain informal fallacies as specific exhibits with slight attempt to analyze them in the general context in which they occur. Informal fallacies, however, are contextually dependent and require analysis in terms of their circumstances of use.

      2. Formal Fallacy: those not dependent on the content of language — i.e., a fallacy that arises from an error in the logical form or structural grammar of an argument; it is (usually) independent of content. Formal fallacies often arise from errors in formal inductive or deductive systems of logic. Informal fallacies normally presuppose a context of disputation: controversy where a question is at issue.

  3. The following chart of fallacies, with some suggestive examples, is an indication of some of the terrain to be discussed in this course:

  4. The classification of fallacies used in these notes is a discomforting oversimplification.

    1. Since errors in reasoning depend upon the type of mistakes made in different evolving logical systems, ideally fallacies should be described in terms of the different kinds of logics. But an attempt to adequately cover these topics in this manner, would, at present, not only be impractical but also would result in a disorganized treatment of fallacies.[17] Since logic is normative, logical pluralism most likely gives rise to different epistemic norms. In a recent influential paper, Hartry Field concludes:
      The upshot of this is a kind of normative pluralism: there are lots of possible norms, and we can rate them as better or worse (relative to our epistemic goals), but there's no reason to think there's a uniquely best one. And talk of correctness of epistemic norm just doesn't seem to make sense.”[18]
    2. And John Woods cogently argues no clear distinction can be drawn in general between fallacies and non-fallacies since many times arguments containing traditional fallacies perform useful functions of abductive and inductive reasoning which are often correct. In these cases it's more reasonable to “commit the error” than to jettison the argument altogether.[19]

  5. Consequently, the assumption taken in these notes is that even a somewhat unsettled organization of fallacy topics is useful in preparation for reasoning in many areas of human inquiry. In debate and other forms of persuasive discourse, the skillful use of fallacies can often be effective in arguments — even though no proof or justification is provided in the argumentative discourse.

    1. Much of the difficulty in studying informal fallacies stems from the fact that in ordinary language fallacies occur in a context such that they are presented with implicitly assumed premises. Often, however, whether or not an argument is being advanced is a question open to interpretation. Often whether or not an argument is being presented is indeterminate. Consequently, in attempting argument reconstruction, the principle of charity ought be followed in so far as possible, with the recognition that misinterpretation or misconstruction of the discourse is always possible.

    2. In our discussion of informal fallacies, an effort will be made not to assume a passage is argumentative unless its context and language strongly indicates that this is the author's intention. If a passage is argumentative, usually but not always, premise and conclusion indicator words are present.

      1. When studying fallacies for the first time, many learners have the tendency to see a fallacies in merely emotive, persuasive, and rhetorical non-argumentative passages. It's important to remember that unless an argument is present, no fallacy could occur.

      2. Thus, the prerequisite for finding a fallacy in a reading is the presence of a logical argument. (An argument must have at least two statements: a premise and a conclusion.)

    3. Some textbooks refer to passages to be analyzed as appeals rather than refer to arguments. The topic of rhetorical appeal, where no argument is present, is properly treated in terms of “disagreements in belief and attitude” as discussed in Logic and Language. The related topic of the distinction between “arguments and nonarguments” is explained in The Nature of Arguments.

There is hardly a subject that dies harder or has changed so little over the years. After two millennia of active study of logic and, in particular, after over half of that most iconoclastic of centuries, the twentieth A.D., we still find fallacies classified, presented and studied in much the same old way. … The truth is that nobody, these days, is particularly satisfied with this corner of logic. The traditional treatment is too unsystematic for modern tastes.

C.L. Hamblin, Fallacies (London: Methuen & Co., Ltd., 1970), 9, 11.


1. C.L. Hamblin, Fallacies (London: Methuen & Co., Ltd., 1970), 9, 14. In addition to On Sophistical Refutations, Aristotle examines a few additional fallacies in his Prior Analytics, On Rhetoric, and Topics.

2. Douglas N. Walton, “Question-Asking Fallacies,” in Questions and Questioning ed. Michel Meyer (Berlin: Walter de Gruyer, 1988), 195. Preview: doi: 10.1515/9783110864205.195.

3. E.g., see Douglas N. Walton, Methods of Argumentation (New York: Cambridge University Press, 2013), 213ff. doi: 10.1017/CBO9781139600187.

4. Francis Bacon does not attend to informal fallacies, but does single out specific “Idols” or illusions in attempting to understand nature, which in some cases correspond to traditional informal fallacies. These Idols or false notions include Idols of the Tribe (general prejudices of human nature such as hasty generalization), Idols of the Den (prejudice of individuals such as experiential bias), Idols of the Market (prejudice arising from verbal confusions), and Idols of the Theater (prejudice such as obeisance to authority). (Francis Bacon, The New Organon, ed. Lisa Jardine and Michael Silverthorne (Cambridge: Cambridge University Press, 2000), §39-44. doi: 10.1017/cbo9781139164030.006

5. Although John Locke describes ad verecundiam (argument from authority), ad ignorantiam (argument from ignorance) and ad hominem (argument against the person) as arguments people employ “in their reasoning with others,” he portrays them as persuasive techniques rather than as fallacies per se. It is only a fourth kind of argument, argumentum ad judicium, proof from foundations of knowledge or probability, which lead to knowledge. (John Locke, An Essay Concerning Human Understanding, ed. A.C. Fraser (New York: Dover Publications, 1959), II:410-411.

6. Prior to offering a tentative classification of fallacy schemes, Douglas Walton et al. writes, “It has proved to be very difficult to classify fallacies. … Fallacies are closely related to schemes … Not only are some schemes subspecies of others, but in many cases the schemes appear to overlap, owing to the difficulty of defining the concepts that any classification scheme has to be based on, including concepts like knowledge, causation, inductive reasoning, expert opinion, consequences, threat, and so forth. For these reasons, any attempt to classify schemes faces inherent conceptual difficulties .“ Douglas Walton, Chris Reed, and Fabrizio Macagno, Argument Schemes (Cambridge: Cambridge University Press, 2008), 348. doi: 10.1017/cbo9780511802034

7. Augustus De Morgan, Formal Logic or the Calculus of Inference, Necessary and Probable (1847 London: Taylor and Walton, 2015), 237. doi: 10.1017/cbo9781107280991

8. H.W.B. Joseph, An Introduction to Logic 2nd. ed. (Oxford: Clarendon Press, 1916), 276.

9. Ludwig Wittgenstein, Philosophical Investigations, trans. G.E.M. Anscombe, 3rd. ed. (New York: Macmillan, 1958), §66-67. This point has also been noted by Robert J. Fogelin and Timothy J. Duggan. They propose a general definition as follows: “[T]he term ‘fallacy” is our most general term for criticizing any general procedure used for the fixation of beliefs that has an unacceptably high tendency to generate false or unfounded beliefs, relative to that method of fixing beliefs. Robert J. Fogelin and Timothy J. Duggan, “Fallacies” Argumentation 1 no. 3 (September 1987), 255-262. doi: 10.1007/BF00136777

10. Boruch A. Brody, “Glossary of Logical Terms,” The Encyclopedia of Philosophy ed. Paul Edwards (New York: Macmillan Publishing and The Free Press, 1967), VI: 64. I.M. Copi, Introduction to Logic (New York: Macmillan, 1961), 52. Seemingly following Copi, Hamblin points out that on the standard view of fallacies, “[a] fallacious argument … is one that seems to be valid but is not so.” Hamblin, 13. This view is discussed in Ralph H. Johnson's “Hamblin on the Standard Treatment,” Philosophy and Rhetoric 23 no. 3 (1990), 153-167. doi: 10.2307/40237632. Hans Vilhelm Hansen, however, shows that defining a fallacy as an argument that seems to be valid but is not so is, in fact, neither a view generally accepted since Aristotle nor generally a view accepted by contemporary logicians. “The Straw Thing of Fallacy Theory: The Standard Definition of ‘Fallacy’,“ Argumentation 16 no. 2(June 2002),133-155. doi: 10.1023/A:1015509401631 Fallacy literature typically reflects Charles Hamblin's 1970 assessment, “The truth is that nobody, these days, is particularly satisfied with this corner of logic. The traditional Treatment is too unsystematic for modern tastes. Hamlin, Fallacies, 11.

11. Hamblin, 14. Quoted from J. A. Oesterle, Logic 2nd. ed. (Englewood Cliffs, N.J.: 1963).

12. Compare with the Frans H. van Eemeren, et al. definition: “Fallacies are violations of the rules for critical discussion that prevent or hinder the resolution of a difference of opinion.” Frans H. van Eemeren, et al. Argumentation: Analysis, Evaluation, Presentation (New York: Routledge Francis and Taylor Group, 2016), 109. doi: 10.4324/9781410602442 Douglas H. Walton extends this “Amsterdam School” definition of fallacy as follows: “A fallacy is regarded as an argumentation technique, based on an argumentation scheme, misused to block the goals of a dialogue in which two parties are reasoning together.” [Douglas H. Walton, A Pragmatic Theory of Fallacy (Tuscaloosa, Alabama: University of Alabama Press, 19950), xi. isbn13: 9780817307981] Rules and schemes such as these often prove to be problematic in application to serious disagreements since criteria for what prevents, hinders, or blocks the resolution of a disagreement are often themselves subject to disagreement among the disputants. Moreover, different types of dialogue and discussion require different rules, and informal fallacies occur in various other contexts than those of two-party argumentation.

13. Gillian Russell, “Logical Pluralism,Stanford Encyclopedia of Philosophy ed. E.N. Zalta (Winter 2016). Till Mossakowski, et al. write, “‘[A] logic’ has come to mean a set of principles for some form of sound reasoning. But in a subject the essence of which is formalization, it is embarrassing that there is no widely acceptable formal definition of ‘a logic.’” “What Is a Logic?,” in Logica Universalis ed. Jean-Yves Beziau, 2nd. ed., (Basel, Switzerland: Birkhäuser Verlag, 2007), 111. doi: 10.1007/978-3-7643-8354-1

14. See Bradley Dowden's discussion of the conflicting definitions of fallacy: “4. What Is a Fallacy?” in his “Fallacies,” Internet Encyclopedia of Philosophy.

15. Ten rules for reasonable discussions are emumerated here: Frans H. van Eemeren and Gob Grootendorst, “A Code of Conduct for Reasonable Discussants,” in A Systematic Theory of Argumentation: The Pragma-Dialectical Approach (Cambridge: Cambridge University Press, 2003), 190-196. doi: 10.1017/CBO9780511616389.009.

16. E.g., Walton's six basic characteristics of fallacy are as follows:
”1. A fallacy is a failure, lapse or error, subject to criticism, correction or rebuttal.
2. A fallacy is a failure that occurs in what is supposed to be an argument.
3. A fallacy is associated with a deception or illusion.
4. A fallacy is a violation of one or more of the maxims of reasonable dialogue or a departure from acceptable procedures in that type of dialogue.
5. A fallacy is an instance of an underlying, systematic kind of wrongly applied techniques of reasonable argumentation.
6. A fallacy is a serious violation, as opposed to an incidental blunder, error or weakness of execution.”
Douglas H. Walton, Methods of Argumentation (New York: Cambridge University Press, 2013), 213-214. doi: 10.1017/CBO9781139600187. Again, these enumerated characteristics are debatable as precisely stated criteria are not specified for the identification of occurrences of failure, lapse, deception, serious violation, reasonable dialogue, wrongly applied techniques, and so on.

17. V. Mendenhall, “Pretending and Port-Royal Logic (Bad Reasoning and Pretend Reasoning),” International Society for the Study of Argumentation Proceedings (Amsterdam: Sic Sat, 1998).

18. Hartry Field, “Pluralism in Logic,” Review of Symbolic Logic 2 no. 2 (June 2009), 355. doi: 10.1017/S1755020309090182.

19. John Woods, Errors of Reasoning: Naturalizing the Logic of Inference (London: College Publications, 2013), 212-216. See also his thoughts on a theory of error: “Error”.

Readings on Nature of Fallacy

Dowden, Bradley. “Fallacies,” Internet Encyclopedia of Philosophy

Finocchiaro, Maurice A. “Informal Logic and the Theory of Reasoning,” Informal Logic 6 no. 2 (1984). doi: 10.22329/il.v6i2.2726

Fogelin, Robert J., and Timothy J. Duggan. “Fallacies” Argumentation 1, no. 3 (September, 1987): 255–262. doi: 10.1007/bf00136777

Hamblin, C.L. Fallacies (1970 Willersey, U.K: Vale Press, 2004).

Hansen, Hans V. and Robert C. Pinto, eds. Fallacies: Classical and Contemporary Readings (University Park: PA: Pennsylvania State University Press, 1995). (blurb)

Hansen, Hans V. “Fallacies,” Stanford Encyclopedia of Philosophy

Hansen, Hans V. “The Straw Thing of Fallacy Theory: The Standard Definition of ‘Fallacy’,“ Argumentation 16 no. 2(June 2002),133-155. doi: 10.1023/A:1015509401631

Johnson, Ralph H. “Hamblin on the Standard Treatment,” Philosophy and Rhetoric 23 no. 3 (1990), 153-167. doi: 10.2307/40237632

Rips, Lance J. “Argumentative Thinking: An Introduction to Psychology and Argumentation,” Informal Logic 29 no. 4 (December 2009), 327-336. doi:10.22329/il.v29i4.2902

Tindale, Christopher W. Fallacies and Argument Appraisal (Cambridge: Cambridge University Press, 2007). doi: 10.1017/cbo9780511806544 (preview)

van Eemeren, Frans, Bart Garssen, and Bert Meuffels. Fallacies and Judgments of Reasonableness (New York: Springer, 2009). doi: 10.1007/978-90-481-2614-9

van Eemeren, Frans H., et al. Fundamentals of Argumentation Theory: A Handbook of Historical Backgrounds and Contemporary Developments. (Mahwah, New Jersey: Lawrence Erlbaum, 1996). doi: 10.2307/358423

Walton, Douglas N. “Defeasible Reasoning and Informal Fallacies,” Synthese 179 no. 3(Apr. 2011) 377-407. doi: 10.1007/s11229-009-9657-y

Walton, Douglas N. Informal Logic: A Pragmatic Approach 2nd. ed. (Cambridge: Cambridge University Press, 2008). doi: 10.1017/CBO9780511808630

Walton, Douglas N. A Pragmatic Theory of Fallacy 2nd. ed. (Tuscaloosa, Alabama: Univ. of Alabama Press: 2003). isbn13: 9780817307981

Weinstock, Michael, Yair Neuman and Iris Tabak. “Missing the Point or Missing the Norms? Epistemological Norms as Predictors of Students' Ability to Identify Fallacious Arguments,” Contemporary Educational Psychology 29 no. 1 (January, 2004), 77-94. doi: 10.1016/S0361-476X(03)00024-9
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