4 Logical Fallacies

By Guest Author

background image 324

Anyone who tries to argue a point is obligated to support assertions with well-reasoned evidence in the form of facts, statistics, illustrations and to support that assertion with reasonableness and logic. There are, however, several very common pitfalls—generally labeled fallacies in reasoning or logical fallacies—waiting for the unwary:

1. Argumentum ad hominem: essentially, an argument or attack on a person rather than the person’s idea. For example, a nationally-televised political commentator, who happened to get his start in show business as a comedian, spoke out against the “Don’t ask, don’t tell” policy, which is a way of circumventing the prohibition against homosexuals serving in the military but keeping that policy in force. One of the proponents of the policy said, “What could he possibly know about this? He’s a comedian!” Instead of focusing on whether the policy itself is good or bad, the speaker launched an attack on the person whose views he didn’t like, which set up a false target and ignored the real issue of disagreement.

2. Non sequitur: literally, “it does not follow.” During a campaign speech, one candidate said to the audience, “If we can land men on the moon, we can find a cure for cancer.” Landing men on the moon, of course, was a triumph of technology, skill, intellect and collective will, but the success of that endeavor has no logical connection to the effort it might take to conquer a disease as complicated and multi form as cancer. In other words, the ability to cure cancer does not follow logically from the ability to land men on the moon.

3. Post hoc: propter hoc—Latin for “after this, therefore because of it.” A simple explanation of this fallacy in logic might go like this: “I came down with a cold this morning. Last night, I went to a concert. I must have caught the cold at the concert.” The essential problem is that there is no logical causal connection between going to the concert and catching a cold.

4. Begging the question: offering as evidence something that needs to be proved is begging the question. Arguing that the car industry in the US is the best in the world, for example, a speaker might say, “Everyone knows that America makes the best cars in the world.” Although this statement might be true, it is not self-evidently true, and to be more than an assertion, such as statement would need to be supported with reasonable evidence.

Want to improve your English in five minutes a day? Get a subscription and start receiving our writing tips and exercises daily!

Keep learning! Browse the General category, check our popular posts, or choose a related post below:

8 Responses to “4 Logical Fallacies”

  • opsimath

    Another well-explained and quite fascinating post, Mr Socco, for which my sincere thanks.

    Sadly, through people’s unawareness of the meaning of ‘beg the question’, it has, here in the UK at least, morphed into something more like ‘prompts/poses the question’, even in organisations, such as the BBC, and they should know better.

    Being so devalued, as many expressions are these days, it is probably advisable to chalk this one up as a lost cause!

  • Ayodeji

    I am so thrilled by the so many write-ups on this site and I found them so very helpful.


  • MadhusudanR

    I’d like to mention the Latin term for the third fallacy: Post hoc ergo propter hoc. It has a ring to it that could be used as a “zinger” in a counter-argument. You know, just mentioning.

    Also, “begging the question” can be called false assumption. Assumptions have to be justified and before that, they have to be reasonable.

    Joe Biden really used these two effectively in his debate against Paul Ryan. Of course, he just laughed them out. Nevertheless, he got these points across.

    A lot of comedy writing depends on violating several of these deliberately. It looks worthwhile to point out that we seem to have an involuntary reaction against bad logic. It is called laughter. Any application of bad logic can be used to construct good comedy.

  • Dale A. Wood

    Note Mr. Scocco: “the effort it might take to conquer a disease as complicated and multi form as cancer”

    “multi form” is bad. “Multi” is a prefix that never stands alone, and it is always attached directly to the root word: “multiform”, no matter what some foreigners migh state. Please e-mail me about this subject: you have my address. Consider the following examples, too.

    multicomputer, multieyed, multifarious, multifingered, multilimbed, multinational, multiply, multistaqe, multistate, multitentacled, multitonal, multivariate, multivibrator, and multiyear.

    Also from science fiction, Isaac Asimv’s famous computer Multivac.

  • Lisa Jey Davis

    I disagree with the point made #1… your argument would have had no merit to anyone hearing it prior to our landing on the moon. Back then, landing on the moon was equally as complex as curing cancer. It would also have no merit to someone who is an aerospace engineer and actually acquainted with the complexities. Sorry – I don’t always disagree in my comments … but these obviously strike me. LOL

  • Lisa Jey Davis

    woops – #2

  • MadhusudanR

    @Lisa: The question is not about the complexity. Also quite obviously, the statement was made in rhetoric. The fact that curing cancer has no dependence on moon landing is the fallacy in concern here. I agree that the rhetoric appeals to the general and vague feeling of “complexity” that people have in their minds. It still doesn’t mean that dealing with one kind of complexity helps us deal with another of a completely different kind. That is the non-sequitur. To just give a silly analogy to highlight the fallacy, it would be like suggesting that Usain Bolt should be able to get a gold in weight-lifting because he got a gold in the 100m dash.

  • venqax

    The fallacy called argumentum ad hominem is very prevalent, I don’t think its example above holds up very well. In fact, offering up a comedian’s political commentary may itself constitute the fallacy of argumentum ad verecundiam (appeal to authority) in its version of an appeal to irrelevant/i> or inappropriate authority. On its face, there is no reason to assume that a comedian would have any expertise on public policy, so it would not lend support to one’s argument to solicit or cite such a source. Unless there was some otherwise unstated reason to grant that the person cited was a recognized relevant authority of some kind, pointing out that he was a comedian—as opposed to policy expert of some kind—would be an appropriate criticism, not an ad hominem fallacy. True, the authority of the information, not the source of it, is what is ultimately decisive but the two can be difficult to separate in practice. I would think more along the lines of those who dismiss the work of a famous painter because he was a pedophile, or besmirch the accomplishments of a scientist because he held supposedly racist attitudes. It’s the “because” that constitutes the fallacy.

    As for ad verecundiam: When a book points out that, “President John F. Kennedy said that Frost was the greatest American poet” as evidence of Frost’s worthiness it is proper to object that a president is no presumptive authority on poetry.

Leave a comment: