What are logical fallacies?

Welcome to The Theology Whisperer, a series of short blog posts on theology and theological education.


What is a fallacy?

In general conversation, any widely held but false belief may be described as a fallacy, or as fallacious. It’s like saying, “Hey, that’s not true.” But in academic writing, a fallacy has a more precise meaning.

Good academic writing involves the presentation of persuasive arguments. A fallacy is the use of invalid reasoning to develop an argument. It is not an actual error but a defect in logic that weakens the argument, undermines the effectiveness of academic writing, and diminishes the credibility of the author. Yet the presence of a fallacy does not necessarily negate an argument; it may simply be a flaw in an otherwise fine argument.

Faulty reasoning

Fallacious arguments may result from sloppy thinking or an intention to deceive. In advertising and political propaganda, as well as academic writing, the persuasive power of an invalid argument may intentionally rely on the use of fallacies to convince an audience that the conclusion is logically valid. The presence of a logical fallacy may deliver what appears to be a persuasive argument, but careful analysis will reveal the faulty reasoning.

There are many reasons why fallacies may mislead us. As Merilee Salmon notes,

Sometimes our emotions interfere with our power to make unbiased judgments. A conclusion can be so attractive that we are ready to accept almost anything offered as evidence in support of it … Alternatively, an assertion may be so repugnant that we will accept almost any statement as evidence against it …

In other cases, we feel a strong like or dislike, or respect or disapproval, for the person who makes a claim … When someone presents a claim in the context of a threat or an enticement, we may fail to notice the lack of evidence…

Another fallacy that plays on emotions is called ‘appeal to pity,’ or ad misericordiam. This occurs when we accord feeling sorry for someone with evidence for the truth of an assertion that is made by or about the person who is to be pitied … Aside from asserting emotional pressure, a fallacy can deceive by its resemblance to a correct form of argument.[1]

The effect of logical fallacies in written or spoken communication is pervasive. As philosopher Michael Withey notes, “There are simply too many bad arguments out there, and their effect is by no means negligible. They lead us to believe pernicious and false ideas, and perpetuate terrible decisions, both on an individual and a collective level.”[2]

It is important to learn to identify logical fallacies in the arguments of others so that you can refute them. It is equally important to learn to detect logical fallacies in your own arguments so that you can avoid them, rendering your writing more cogent and your reputation more reliable.

Two kinds of fallacy

Fallacies may be categorised in various ways. The most common distinction is between formal and informal fallacies. If the faulty reasoning lies in the form (that is, the structure) of the argument, it is called a formal fallacy. If the faulty reasoning lies in the content of the argument, it is called an informal fallacy.[3]

Formal fallacies are those possessing some error in the structure of their logic: their form is wrong. These include affirming the consequent, conclusion denying premises, contradictory premises, denying the antecedent, exclusive premises, existential fallacy, false conversion, minor/major illicit process, positive conclusion/negative premises, Quaternis terminorum, and the undistributed middle. You should always reject formal fallacies because they violate the basic rules of logic.

Informal fallacies are those which use valid reasoning on terms which are not of sufficient quality to merit such treatment: their content is wrong. There are many of these. Examples include ad hominem, bifurcation, blinding with science, collective guilt, emotional appeal, equivocation, false zero-sum game, hedging, “if it saves lives,” poisoning the well, red herring, shifting ground, slippery slope, straw man, and Thatcher’s blame.

Most fallacies you encounter will probably be informal ones, and these should likewise be rejected. They are usually more difficult to identify and rebut than formal fallacies, because you need to examine not only the content of the premises and conclusion but also the use to which the argument is put, checking its validity on a case-by-case basis.[4]

My next two posts will outline the most common logical fallacies and give examples of each.


This post was written by Rod Benson. Leave a comment in the box below, or email theologywhisperer@gmail.com 


[1] Merrilee H. Salmon, Introduction to Logic and Critical Thinking (6th edn; Belmont, CA: Wadsworth, 2013), 98-99.

[2] Michael Withey, Mastering Logical Fallacies: The Definitive Guide to Flawless Rhetoric and Bulletproof Logic (Berkeley, CA: Zephros Press, 2016), 12.

[3] For other ways of categorising fallacies see http://www.ilas.nagoya-u.ac.jp/~nilep/fallacies.html and Madsen Pirie, How to Win Every Argument: The Use and Abuse of Logic (2nd edn; London: Bloomsbury, 2015), 218-222.

[4] See examples in Withey, Mastering Logical Fallacies, 11.

Image source: qz.com

2 Replies to “What are logical fallacies?”

  1. You’ve got to watch those emotions! Can I ask for a more careful evaluations of the suspicion of emotions so beloved of certain brands of academics and theologians. Is there a place for good emotions and intuitions, or does God only speak in logic?

    1. Good point, Alan. My post is not intended to diminish or dismiss the natural role emotions play in academic discourse as in general personal and communal life. As David Hume might say, in one sense emotions are everything.

      But if you’re referring to my use of the quote by Merilee Salmon, the first sentence in the quote is crucial: “Sometimes our emotions interfere with our power to make unbiased judgments.” That goes to the heart of my wariness of deploying emotion in academic argument: it is a tactic often used to mask poor logic, or to persuade when the evidence or argument can’t do the job.

      As for your question about whether God only speaks in logic, I see where you’re going and will simply say that the God and Father of our Lord Jesus Christ is a person and not a machine.

Comments are closed.

%d bloggers like this: