Tuesday, December 28, 2010

The Wrong Way to Argue

In this blog, I will be referring frequently to several established “logical fallacies.”  Unfortunately, these are not covered in high school or even most college curricula, so I feel it is probably necessary to briefly go over what a fallacy is and discuss a few key types of fallacies before moving forward.  If you are going to be a regular reader, I would highly recommend familiarizing yourself with this information; otherwise you might get a little lost in some of my forthcoming posts!
The two places where I learned the most about formal logic and fallacies were the websites of the New England Skeptical Society in the article “How To Argue” and the Skeptics Guide’s article “Top 20 Logical Fallacies”.  I highly recommend giving both of these sites a visit.  They were also the two primary sources I used for this blog (or is it post?  Someone please clear this up for me.)  You can visit these sites in the links below.

For the purpose of the following post, I will be using several examples to illustrate fallacies.  Since these are for illustrative purposes, I have reduced certain arguments to simplistic terms.  I am not in any way infantilizing those who make these arguments—just boiling the arguments down in order to use them as easy-to-follow examples. 

What is a logical fallacy?

All arguments have the same basic structure: A therefore B. They begin with one or more premises (A), which is a fact or assumption upon which the argument is based. They then apply a logical principle (therefore) to arrive at a conclusion (B). An example of a logical principle is that of equivalence. For example, if you begin with the premises that A=B and B=C, you can apply the logical principle of equivalence to conclude that A=C. A logical fallacy is a false or incorrect logical principle. An argument that is based upon a logical fallacy is therefore not valid. It is important to note that if the logic of an argument is valid then the conclusion must also be valid, which means that if the premises are all true then the conclusion must also be true. Valid logic applied to one or more false premises, however, leads to an invalid argument. Also, if an argument is not valid the conclusion may, by chance, still be true.

Types of Fallacies


The term “non-sequitur” is Latin for “does not follow.”  If A=B and B=C it does not follow that A=F.  This is used when someone tries to imply a connection where there is none.  A basic example of this might be “the universe exists, therefore a god must exist that created it.”  It does not follow that a god must exist because the universe might have been brought into existence naturally through quantum fluctuation, as physicists like Lawrence Krauss have hypothesized, or the universe might be infinite, existing in an unending continuum of “Big Bang, inflation, expansion, contraction, Big Crunch, Big Bang, etc.” as other physicists have begun to claim, or it might be just one universe in an infinite sea of universes, all part of a larger “multiverse.” 

This is the simplest fallacy and is actually the basis for all or most other logical fallacies.

Ad Hominem

Ad hominem arguments are personal attacks on an individual making a particular argument.  These are designed to discredit the claimant rather than the claim.  An example might be “Stephen Hawking only claims there is no god because he is angry at god for making him disabled” (a real statement made by a Christian on a message board about Hawking’s recently professed atheism.)  This is fallacious because nothing prevents an incredible (incredible used as a negative) person from making a true claim. 

However, it is not always fallacious to use the ad hominem—it is sometimes legitimate based on the circumstances.  For instance, if a politician claims that he would be the best candidate for office because he is the most honest, it would not be fallacious to point out a financial scandal that he had been involved with. 

Ad Ignorantiam

Ad ignorantiam arguments, also called Arguments from Ignorance, are basically arguments that state “we do not understand X, therefore Y must be true.”  This is often used by proponents of so-called Intelligent Design, who argue that because scientists do not fully understand, for instance, the evolution of the bacterial flagella motor or a-biogenesis, those processes must have been manipulated by an intelligent designer of life (i.e. Yahweh.) 
This argument is fallacious because it lacks positive evidence for its own claims.  It relies on the absence of evidence for other claims (as opposed to contradictory evidence for other claims or positive evidence for its own) and then assumes that its own claim wins by default.  If we have no positive evidence for claim X and no positive evidence for claim Y, then we cannot pick one claim over the other.  We must wait until more evidence becomes available.  Also, the absence of evidence for claim X does not constitute evidence for claim Y.  The absence of another explanation only means that we do not know – it does not mean we get to make up a specific explanation.

This argument, particularly when used by creationists and Intelligent Design proponents, has been rechristened by Richard Dawkins (in a rather tongue-in-cheek way) as the Argument from Personal Incredulity. 

Argument from Authority

This argument usually goes as follows:  Professor A is very qualified, Professor A believes B.  Therefore B is true.  Often this argument is implied by emphasizing the many years of experience, or the formal degrees held by the individual making a specific claim. The converse of this argument is the ad-hominem logical fallacy (above.) 

In practice this can be a complex logical fallacy to deal with. It is legitimate to consider the training and experience of an individual when examining their assessment of a particular claim. Also, a consensus of scientific opinion does carry some legitimate authority.

But it is still possible for highly educated individuals, and/or a broad consensus to be wrong.  Speaking from authority does not make a claim true.  Therefore, we cannot say “Isaac Newton believed in alchemy, Isaac Newton was very intelligent, alchemy must work.” 

Post Hoc Ergo Propter Hoc

This fallacy can be summed up as “correlation does not equal causation.”  Basically, it assumes that because X followed Y, Y caused X.  However, this is not always true.  For instance, Z could have been happening at the same time as X and Z could have caused Y instead.  Or Y could have happened regardless of whether or not X happened. 

For instance, many liberals have claimed that the financial crisis and ensuing recession happened under President George W. Bush, therefore conservative economic policies lead to recession.  Obviously, this is Post Hoc Ergo Propter Hoc because we know that the financial crisis had much deeper and more systemic causes than Bush’s economic policies—causes rooted in the culture of the financial industry and in government policy going back several decades. 

False Continuum

False continuum's state that because there is no definitive demarcation line between two extremes the distinction between the extremes is not real or meaningful: There is a fuzzy line between cults and religion, therefore they are really the same thing.

False Dichotomy

A false dichotomy arbitrarily reduces a set of many possibilities to only two.  For instance, a politician tells you that we must convert to a single-payer healthcare system, otherwise the health insurance companies will run amok, overcharge you and under-insure you.  This assumes that the only two choices are complete industry self-regulation and complete government subsidization.  In fact, there is a vast middle-ground, including light regulation, strict regulation, pricing caps, antitrust legislation, public option insurers, individual mandates, healthcare subsidies, etc. 

Slippery Slope

This logical fallacy is the argument that a position is not tenable because the extreme of the position is undesirable. But holding a moderate position does not necessarily require one to hold the extreme progression of that position.  For instance, a libertarian might advocate for less government intervention into private industries like manufacturing, but still be opposed to the repeal of all minor labor laws. 

Special Pleading or Ad-Hoc reasoning

Ad-hoc reasoning or special pleading involves revising ones argument by setting a special premise to explain away contradictory evidence.  The special premise itself must not be justified in order for the argument to be considered ad-hoc. 
For instance, a six-day creationist may claim that the world is six thousand years old.  However, there are stars and galaxies in the night sky which we would not be able to see unless the universe were billions of years old.  Also, the Earth contains many features that only a planet billions of years old could contain.  The creationist would then resort to special pleading by claiming that God created the universe and the Earth “with age”—i.e. a 13.7 billion-year-old universe was brought into existence six-thousand years ago. 
Straw Man
A straw man argument is one wherein you superimpose a position which will be easy for you to argue against onto your opponent, regardless of whether or not your opponent actually holds that position.  For instance, it would be a straw man argument for me to argue against the prohibition of condoms by the Catholic Church if I were debating with a Catholic who happened to disagree with that particular church policy. 

Circular Reasoning

In circular reasoning, the conclusion of the argument is also its own premise. The structure of such arguments is A=B therefore A=B, although the premise and conclusion might be formulated differently so it is not immediately apparent as such. For example, saying that therapeutic touch works because it manipulates the life force is a circular, because the definition of therapeutic touch is the alleged manipulation (without touching) of the life force.

No True Scotsman Fallacy

This is a very particular fallacy—a type of special pleading—wherein a positive trait is assigned to an entire group (the group being defined by something other than the positive trait.)  If there are any individuals within the group who do not possess the positive trait, then those specific individuals are not considered ‘true’ group members.  This also becomes circular, because having the positive trait that is asserted to be possessed by the group becomes a requirement for inclusion as a ‘true’ group member. 

For instance, I might claim that “Scotsmen are great athletes,” then an objector might retort, “ah, but here are some Scotsmen who are terrible athletes.”  I would then respond, “Aye, but they are not true Scotsmen.  True Scotsmen are great athletes.” 

Shifted Burden of Proof

When one makes a positive claim that X exists, one takes on the burden of proving that claim.  When one makes a negative claim that X does not exist, then one takes on the burden of refuting the evidence and arguments used to support X but not the burden of proving that X positively does not exist. 

A shifted burden of proof argument relies on demanding that the individual making the negative claim actually proves the negative.  For instance, a UFO believer might say “you can’t definitively prove that all of the UFO sightings ever reported are not alien spacecraft, therefore I am going to believe that some are.” 


Hopefully, having this information will help you understand a little more about both the arguments I make on this blog as well as arguments in your own life.  If you ever see me making any of these fallacies, then feel free to point it out.  Knowing how to properly assess claims and determine if they are legitimate is a fundamental necessity to anyone in life—otherwise you will be taken for a ride.  


  1. Here are the links to the articles from the Skeptic's Guide and the New England Skeptics Society.



  2. Blog can actually mean both of those since it is both a noun and a verb

    noun: contraction for "web log", a type of online diary

    verb: to post diary or journal entries to a web log

  3. I hope you keep these in mind in future arguments against Christianity and theism. ;-)

  4. Oh, I definitely will--since there has never been an argument supporting the existence of the Christian god that does not rely on a logical fallacy (or an unfalsifiable claim or a demonstrably false claim), this information is very good to keep in mind!

  5. "since there has never been an argument supporting the existence of the Christian god that does not rely on a logical fallacy (or an unfalsifiable claim or a demonstrably false claim)"...hahaha, right on.