A brief of logical fallacies

On this page I am going to create a list of logical fallacies which I will be adding to over time.

Post Hoc Ergo Procter Hoc

Translates from latin to After this, therefore because of this. This one is used often by alternative medicine proponents as proof that their treatments actually work, often given in the form of a testimonial. Just because something was previous to another thing, doesn’t mean it had any affect.
Example: Aunt Merle knitted me a new  sweater at the start of this year,
I didn’t get this flu this winter,
Aunt Merle’s Sweater prevented me from catching the flu.
This is not strictly true as the flu vaccine may have prevented it, or this person might not have caught the flu anyway this year.

Argument from ignorance

This fallacy is most commonly used by creationists and religion proponents in the form of:
We don’t know exactly how the big bang happened,
God did it.
This fallacy fails to account for the fact that there has been a steady decline in our ignorance  over the years from believing that Thor banging his big hammer to make all the lightning, to god being a benign being who just wrote the rulebook and then watched it all unfold. We cannot say that a lack of information in a certain area is proof of something, it just shows that we are ignorant of the subject.
This fallacy also includes in it the God of the Gaps fallacy, which in its most common form states:
There are gaps in the fossil record between species,
Evolution does not exist.

Ad Hominem Attack

An ad hominem attack is when one rebutts an argument by insulting the arguer, rather than addressing the argument put forward by the arguer. This Fallacy is used by almost every pseudoscience towards skeptics, usually under the guise of “Your just a closed-minded skeptic”. The best way to address these arguments is to point out their fallacy, and if they continue to make ad hominem attacks, ignoring them is really the only solution. What you must never do though, is make another ad hominem attack back at them, this plays right into their hands. Most often a skeptic will fall into this trap by calling a pseudoscience stupid. This is OK if after titling a claim ‘stupid’, the skeptic goes on to tell everybody exactly why it is stupid.

Argument from Authority

Basically, the argument from authority is that a belief is true because a professor says it is true. This is usually accompanied with a big spiel about the amount of years the professor has spent in the scientific realm. The inverse of this argument is that a belief is wrong because no authority believes the claim. (this can also be filed as an ad hominem attack)

This argument is not valid because just because an authority says something is true, does not mean it is true.

This logical fallacy is tricky because it does hold some water. For example, you wouldn’t trust a paper from a scientist who has been known to produce fraudulent data before, and a consensus of scientific opinion also holds some legitimate authority. It is when an argument is based entirely on one scientist (or a small group) that some concern should be raised as to the legitimacy of the argument.

Argument From Final Consequences

also known as a teleological argument, this simply states that because somebody benefited from an event, then they must have been behind this event.

A benefited B
A was caused by B

This argument was thrown around by conspiracy theorists after the death of Osama Bin Laden, saying, “Isn’t the timing of Bin Laden’s death very convenient for Obama’s re-election.”
This argument is wrong for a couple of reasons, firstly, with such a big thing as the death of the mastermind behind the 911 attacks, it is hard for it not to influence somebody in politics.
It is also wrong because there are a lot of things people have done which have directly influenced them negatively, and also a lot which has influenced people positively which they have nothing to do with.

Argument from Personal Incredulity

This is a subset of the argument from ignorance, and is also used by creationists, for example
I cannot imagine amoeba evolving into humans and dogs and cats and horses and frogs and snakes and apes and Charlie Sheen in just 3.4 billion years, therefore, evolution is not possible.

Begging the Question

also known as circular reasoning, this is a common argument from biblical proponents, and it goes a little like this,
Religious person: God is true because the bible says it is true,
Skeptic: How do you know the bible is true?
Religious person: Because it is inspired by god.

This is circular reasoning because the argument only holds if the argument is right.

Correlation equals Causation

This argument is used very commonly in everyday life by regular people such as,
I have a sore back
I went to the Chiropractor
My back got better
The Chiropractor fixed my back.
This is not true because your back may have gotten better even if you didn’t go to the chiropractor, or it may have been fixed by something else, other than the Chiropractor.

This argument is not valid because there is no way of knowing whether it was the chiropractor who fixed your back or not, in such complex systems such as life, a lot of different variables are at work, and there is no way of knowing which had an effect. Whole pages of alternative medicine websites are based on this fallacy, under the tab… Testimonials.
This is bad evidence because it bypasses all of the rigor of a scientific study.

Confusing unexplained with unexplainable

This is a common fallacy employed by creationists to argue that because we don’t currently know how life on earth began, it is therefore defying the laws of nature and it is needed for a god to explain it.

False Analogy

Let it be known that an analogy is not a logical fallacy. Analogies or very important in arguments as they allow for us to explain our arguments using a story that everybody can understand. However, an analogy becomes fallacious when it is not entirely correct, and it does not bear any resemblance to your argument.

A common false analogy is used by creationists to argue for design in the universe or the evolution of living material. They often say something similar to “The chance of evolution creating what we see today is like a car junk-yard blowing up and creating from it a shiny new car”
This analogy is untrue because evolution is not just an explosion of random events, it is the slow, gradual, selected change of organisms to incorporate favoured genes into the gene pool.

False Continuum

The idea that because there are grey areas between two extremes they are actually the same thing, is a logical fallacy. For example:-
There are fuzzy areas between religion and cults, therefore they are really the same.

False Dichotomy

The opposite of a false continuum, this is essentially reducing your options to just two.
For example creationists say that there are gaps in the fossil record, therefore the earth must be 6000 years old and created by god. This is reducing the possibilities to either yours our mine, which is not always true. This argument can also be used to over simplify a spectrum. For example, science and pseudoscience are not two completely different entities, rather that there are some which fall about half way on the spectrum, which have characteristics of both science and pseudoscience, such as SETI.

The Genetic fallacy

This argument is not talking about genetics as in DNA, but to history and it is often used by creationists. It often comes in the form of the creationist making an out-of-context quote from an evolutionary biologist, and then continuing to argue against this quote, rather than the arguments put forth by the person they are arguing against.


Also known as hypocrisy, this argument is essentially applying a set of rules or criteria to one argument, but not to another argument.
For example, alternative medicine advocates often say that we need stronger regulation on prescription drugs to ensure safety and effectiveness, and then go on to say that medicinal herbs should be able to be sold without any regulation.

No true Scotsman

This argument is similar to circular reasoning, and it is often explained like this.
Sean claims that all Scotsmen are brave. Brian then produces a counter argument which shows that some Scotsmen really are cowards. Sean then proceeds to claim “well then he’s no true Scotsman.” By saying this, Sean has redefined ‘Scotsman’ to include in the definition as having a brave personality. This argument does not produce any new information about the subject, and is limited to Sean’s definition of ‘Scotsman’.

Non Sequiter

This translates in latin to doesn’t follow. This is the logical fallacy where the conclusion does not necessarily flow from the premace. A logical connection has been made where none exists.

Reductio Ad Absurdum

In formal logic, this is a valid argument. It says that if one premace is true, and it leads to an absurd conclusion, it is false. This is more often used nowadays as an abuse of this argument. It is often used by UFO enthusiasts, who say “If you are skeptical of UFOs because you have not seen one with your own eyes, you must also reject the existence of the great wall of China. because you have not seen that with your own eyes.
This is an abuse of the reductio ad absurdum argument because it means that the UFO enthusiast is only limiting his proof to personal eyewitness, and not allowing other proofs.
In fact, most skeptics believe that a lot of things exist, despite nobody ever seeing one with their own eyes. This is true for neutrinos, black holes, the nucleus of an atom and the existence of quantum fluctuations.

Slippery Slope

This is the logical fallacy which makes the assumption that accepting one mild position will eventually lead to a very extreme position being excepted.
For example:
If Australia becomes a republic then soon enough we will become like China, with very few human rights and no true democracy.
This argument is incorrect because there are plenty of republics in the world which have fair human rights, and an egalitarian democracy, like The USA or France.

Special Pleading

also known as ad-hoc reasoning. This is often a very subtle fallacy. It is essentially the introduction of new elements to a phenomenon to explain away contradicting evidence or logic. The most common use of this fallacy is by ESP proponents. When shown tests which are negative towards ESP, they often claim something similar to “ESP doesn’t work in the presence of skeptics.” This process will often be taken to the extremes, and very ridiculous ad-hoc reasoning can take place.

Straw Man

This is a common fallacy which is used by creationists. They will often data-mine their way through dozens of books, articles and write-ups from a respected evolutionary biologist, and try to find one paragraph that they can refute. Once they have done their rebuttal of the paragraph, they will claim that they have disproved evolution.
It is essentially the attacking of a weak, made up position which is easier than attacking the real position in order to make the arguments for evolution sound weak.

This argument is also used by Alternative medicine proponents. They will argue that skeptics just refuse to accept alternative medicine for the basic fact that it conflicts with their world view. However, this is not true, if you read skeptical articles on alternative medicine, you will find that the reasoning behind a skeptics rejection of alternative medicine is much more thought out than what alternative medicine proponents will let you believe.


4 thoughts on “A brief of logical fallacies

  1. This argument is wrong for a couple of reasons, firstly, with such a big thing as the death of the “mastermind behind the 911 attacks”?? Facts Please!, it is hard for it not to influence somebody in politics.

  2. Pingback: Weekly Roundup #1 | Skeptical Monsters

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