Logical Fallacies

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What is a logical fallacy?

A logical fallacy is, at its essence, an error of reasoning. When an argument is used, based on bad reasoning to support a position (or to try to convince someone to adopt the same position), it is considered a fallacy.

Appeal to Antiquity or Tradition
A common logical fallacy that occurs when it is assumed that something is better or correct simply because it is older, traditional, or “always has been done.”

Example
Homeopathy has been around 200 years, so obviously it must work.

Appeal to Common Belief
Also known as the Argumentum ad populum, it is the claim that most or many people in general or of a particular group accept a belief as true is presented as evidence for the claim. Accepting another person’s belief, or many people’s beliefs, without demanding evidence as to why that person accepts the belief, is lazy thinking and a dangerous way to accept information. This is used by many anti-science arguments by stating that because 90% of Americans believe that X is true, then X must surely be true.

Example
Over 60% of Americans believe creationism is true, so evolution must be false.

Appeal to Consequences
An attempt to motivate belief with an appeal either to the good consequences of believing or the bad consequences of disbelieving, without respect to the quality of the evidence supporting such an argument. Of course, there may be consequences to a belief, as long as it is supported by evidence.

Example
Belief in evolution will lead to mass genocide.

Appeal to Nature
Similar to the naturalistic fallacy, when used as a fallacy, is the belief or  suggestion that “natural” is always better than “unnatural”. It assumes that "nature" is good, and "unnatural" is not. Unfortunately, in many discussions about science and medicine, individuals take this as their default belief.

Example
High fructose corn syrup is not natural so it must be bad for you.

Appeal to Novelty
The opposite of the Appeal to Antiquity, is an argument that the novelty or newness of an idea is itself evidence of its truth. Since every rejected idea in the history of man was once a "novel idea," the fallaciousness of this argument is apparent.

Example
If you want to lose weight, your best bet is to follow the latest diet.

The Fallacist’s Fallacy
Also known as argument to logic (argumentum ad logicam), fallacy fallacy, or fallacist's fallacy, is dismissing a proposition because on of its supporting arguments contains a logical fallacy. In other words, the rejection of an idea as false simply because the argument used to support the idea is itself
fallacious. Just because one argument lacks merit or is fallacious, that it is not sufficient evidence to reject the idea.

Example
Tom: OK — I'll prove I'm English — I speak English so that proves it.
Bill: But Americans and Canadians, among others, speak English too. You are assuming that speaking English and being English always go together. That means you are not English.

Argument from False or Misleading Authority
Also argumentum ad vericundiam, is a logical fallacy which provides an argument from an authority, but on a topic outside of the particular authority's expertise or on a topic on which the authority is not disinterested (i.e., is biased). Almost any subject has an authority on every side of the argument, even where there is generally agreed to be no argument. When correctly applied, it can be a valid and sometimes essential part of an argument that requests judgement or input from a qualified or expert source. The works (almost always published and peer-reviewed) of authorities, no matter how eminent or influential, is always judged by the quality of their evidence and reasoning, not by their authority alone.

Example
Dr. Smith, an expert in computer engineering, does not believe in climate change, so obviously climate change is false.

Argument from Ignorance
Infers that a proposition is true from the fact that it is not proven to be false (or alternatively, that a proposition is false because it is not proven to be true). The old argument that "the absence of evidence is not evidence of absence" is a form of this logical fallacy, because absence of evidence can be evidence of absence if substantial attempts to find evidence have proven negative. The fallacy also asserts that a proposition is true because it has not yet been proven false, or it is "generally accepted" (or vice versa). Furthermore, this argument presumes that there are only two choices: true or false. In fact, there are other choices, including "not enough investigation has been completed to choose between true or false." So a non-fallacious argument may be made that a proposition is not false because insufficient testing has been done to show it false. That is a reasonable argument. Appeals to ignorance are used to shift the burden of proof to the other side. However, the burden of proof should be on the side that is making the assertion, not on the side that disputes the assertion.

Example
There is no evidence that says a god doesn't exist, so a god must exist.

Argumentum Ad Hominem
Ad hominem argument applies to any argument that centers on emotional (specifically irrelevant emotions) rather than rational or logical appeal. An ad hominem argument occurs when one attacks the person making an argument rather than the argument itself.

Example
You're a shill for Big Pharma so any of your statements about vaccine safety can't be trusted because Big Pharma is paying you off.

Bandwagon Fallacy
Committed by an argument that appeals to the growing popularity of an idea. This popularity is used as the reason for accepting it as true. Such an argument is fallacious because popularity may not arise from an actual fact, but may result from peer pressure, political expediency, or even plain mass stupidity. Popularity does not guarantee the truthfulness of an argument.

Example
Creationism is supported by most Americans, so it must be true.

Cherry Picking or Quote Mining
A fallacy where only select evidence is presented in order to persuade the audience to accept a position, and evidence that would go against the position is withheld. The stronger the the withheld evidence, the more fallacious the argument. Quote mining is a form of cherry picking, and the genuine points used in construction of straw man arguments are typically cherry-picked.

Example
You should be a Christian, because God is all about love and forgiveness, and those are great things.

Confirmation Bias
The tendency for individuals to favor information or data that support their beliefs. It is the tendency for people to only seek out information that conforms to their pre-existing view points, and subsequently ignore information that goes against them. It is a type of cognitive bias and a form of selection bias toward confirmation of the hypothesis under study. Avoiding confirmation bias is an important part of rationalism and in science in general. This is achieved by setting up problems so that you must find ways of disproving your hypothesis (see falsifiability).

Example
Psychic "readings" is that listeners apply a confirmation bias which fits the psychic's statements to their own lives. By making a large number of ambiguous statements in each sitting, the psychic gives the client more opportunities to find a match. This is one of the techniques of cold reading, with which a psychic can deliver a subjectively impressive reading without any prior information about the client.

Fallacy of Composition
An incorrect inference that the qualities of the whole can be made from the qualities of one of its parts. It is the opposite of the Fallacy of Division.

Example
Human cells are invisible to the naked eye.
Humans are made up of human cells.
Therefore, humans are invisible to the naked eye.

False Dichotomy
False dilemma is a dichotomy (a set of two mutually exclusive, jointly exhaustive alternatives) of arguments that ignores the potential for an infinite set of alternative arguments; for an infinite number of overlapping arguments; or for the potential that neither part of the dichotomy is correct. A false dichotomy is often employed by an arguer to force the other side into an extreme position by assuming that there are only two possible positions. At its essence, it says "you are either with us or against us," which ignores the all other possibilities, such as "we are with you on points A&B but against you on points C,D,&E."

Example
Because evolution has not been unable to show exactly how life arose, evolution is therefore disproved, and creationism is obviously the correct answer.

False Equivalence
A logical fallacy where there appears to be a logical equivalence between two opposing arguments, but when in fact there is none. Journalists use a form of this logical fallacy when comparing two sides of a scientific debate in an attempt to provide a balance between a scientific and denialist point of view. However, there is no equivalence between the two sides, when one is supported by evidence, and the other side with little or no evidence, of which most is of low quality. In other words, in false equivalence, someone will state that the opposing arguments have a passing similarity in support, when, on close examination, there is large difference between the quality of evidence.

Example
Marijuana and alcohol are both drugs. An ounce is about the same as three bottles. If you think one should be legal, you should think the same of the other.

Fallacy of Division
An incorrect inference that the qualities of the parts can be deduced from the characteristics of the whole. It is the opposite of the Fallacy of Composition.

Example
Humans are visible to the naked eye.
Humans are made up of human cells.
Therefore, human cells are visible to the naked eye.

Fundamental Attribution Error (or Correspondence Bias)
(also known as correspondence bias or attribution effect) describes the tendency to over-value dispositional or personality-based explanations for the observed behaviors of others while under-valuing situational explanations for those  behaviors. The fundamental attribution error is most visible when people explain the behavior of others. It does not explain interpretations of one's own behavior—where situational factors are often taken into consideration. Fundamental attribution error is a social/psychological bias, is not a true logical fallacy. However, it is frequently used in arguments or debates.

Example
As a simple example, if Alice saw Bob trip over a rock and fall, Alice might consider Bob to be clumsy or careless (dispositional). If Alice tripped over the same rock herself, she would be more likely to blame the placement of the rock (situational).

Galileo Gambit
A fallacy where the putative expert insists that he is an unacknowledged genius, a maverick who is shunned by mainstream science because of his unconventional ideas.

Example
I am an expert in vaccines, because I have a Masters of Public Health, but my brilliant and radical ideas have been rejected by mainstream medicine because Big Pharma and the CDC are suppressing my ideas because my knowledge will disrupt all of our knowledge about vaccines.

Gambler's Fallacy
The fallacy of assuming that a short-term deviation from statistical probability will be corrected in the short-term. In a totally random event, past performance has no effect on the next attempt. Arguing that a totally random event may have a result that will self-correct the "average" is fallacious. It is the false belief that a random process becomes less random, and more predictable, as it is repeated. This is most commonly seen in gambling, hence the name of the fallacy. For example, a person playing craps may feel that the dice are "due" for a certain number, based on their failure to win after multiple rolls. This is a false belief as the odds of rolling a certain number are the same for each roll, independent of previous or future rolls.

Example
1. This coin has landed heads-up nine times in a row. Therefore,
2. It will probably land tails-up next time it is tossed.

This inference is an example of the gambler’s fallacy. When a fair coin is tossed, the probability of it landing heads-up is 50%, and the probability of it landing tails-up is 50%. These probabilities are unaffected by the results of previous tosses.The gambler’s fallacy appears to be a reasonable way of thinking because we know that a coin tossed ten times is very unlikely to land heads-up every time. If we observe a tossed coin landing heads-up nine times in a row we therefore infer that the unlikely sequence will not be continued, that next time the coin will land tails-up. In fact, though, the probability of the coin landing heads-up on the tenth toss is exactly the same as it was on the first toss. Past results don’t bear on what will happen next.

Genetic Fallacy
Creates an argument that is accepted or rejected based on the source of the evidence, rather than on the quality or applicability of the evidence. It is also a line of reasoning in which a perceived defect in the origin of a claim or thing is taken to be evidence that discredits the claim or thing itself.

Example
He has a medical degree and doesn't like vaccines, so obviously vaccines are bad.

Gish Gallop
Occurs when the putative expert slickly rattles off a long list of assertions without providing evidence or allowing questions.

Example
And just because YOU don’t know how the cheese is created on the moon, doesn’t mean that there isn’t a cheese creating mechanism at the core of the moon. Run by secret moon wizards. And there are moon cows, that only live on the far side of the moon, eating moon grass that grows during the 14.25 days of the month where it’s illuminated – presumably spending the remaining 14.25 days in hibernation or possibly storing metabolite like cacti. Naturally, since the crust is mostly rock, then the grass would be mostly rock too, leading to heavier milk and cheese. There’s your Occam’s Razor! All you need to do is assume the existence of a completely novel form of biological life and the explanation becomes simple! Even more so when this neatly explains the motivation for Big Milk – moon cheese is much more valuable than “earther cheese” and only the superwealthy can afford the biological processing necessary to make it edible instead of poisonous which is why only the super-rich members of the Illuminati and Freemasons know about it. NOW IT ALL MAKES SENSE!!!!!

Naturalistic Fallacy
Similar to the appeal to nature, where the conclusion expresses what ought to be, based only on actually what is more natural. This is very common and most people never see the problem with these kind of assertions due to accepted social and moral norms. This bypasses reason and we fail to ask why something that is, ought to be that way.

Example
Homosexuality is morally wrong because, in nature, sex is used for reproduction.

Nirvana Fallacy
An attempt to compare a realistic solution with an idealized one, and dismissing or even discounting the realistic solution as a result of comparing to a “perfect world” or impossible standard. This reasoning ignores the fact that improvements are often good enough.

Example
What’s the point of making drinking illegal under the age of 21? Kids still manage to get alcohol.

Non Sequitur
The Latin phrase for "(it) does not follow."It means that the conclusion reached does not follow from the premise(s). Examples of "non sequitur" arguments are hilariously disconnected, but often they can be subtle and may not be easily uncovered. The arguments are fallacious since they do not provide any evidence for an argument and are just meant to confuse the listener.

Example
Homeopathy comes in pretty bottles. Therefore, homeopathy can cure cancer.

Poisoning the Well
To pre-provide any information that could produce a biased opinion of the reasoning, positive or negative. It is related to the ad hominem argument.

Example
Remember, Big Pharma supports vaccines, so any research that supports vaccines should be examined carefully.

Post Hoc Ergo Propter Hoc
Also known as the post hoc, Post hoc ergo propter hoc is a Latin phrase, literally translated as "after this, therefore because of this." It is a fallacious argument that states that because a second event follows the first, the first event must be the cause of the second. Many superstitions are based on this type of argument, because the observer may notice that performing one action seems to lead to another. Although post hoc observations may lead to a testable hypothesis, there must be evidence of a mechanism that extends the correlation to causation.

Example
My child broke her leg after she was vaccinated, so vaccines cause broken legs.

Shill Gambit
A type of ad hominem and poisoning the well, wherein one party dismisses the other's argument by proclaiming them to be on the payroll of some company. Sometimes known as the Big Pharma Shill Gambit or the Monsanto Shill Gambit. The shill gambit is used fallaciously when the only "evidence" given of such a connection to a big company or government is the endorsement of the position of the government or company, without any other evidence–the implication is that they provide that endorsement only because they receive some sort of compensation from the company or other agency. On the other hand when such conflict of interest is both demonstrated by verifiable evidence and can be shown to interfere with a person's judgement of the evidence, then it's no longer a logical fallacy.

Example
The writer is only endorsing the safety and effectiveness of vaccines because he's secretly paid by Big Pharma.

Slippery Slope Fallacy
These are arguments that utilize the false assumption that once a first step is taken, it predicts the next step, which then leads to the next step until some conclusion is reached that supports the initial idea. The arguer then concludes that we therefore shouldn’t do the first thing. There are several issues with this type of fallacy, specifically, it makes a prediction that simply cannot be proven. It also assumes that there isn't a restraint placed on subsequent steps that modify the conclusion.

Example
If you teach evolution in school, you start down the slippery slope to immorality.

Special pleading
A form of spurious argumentation where a position in a dispute introduces favorable details or excludes unfavorable details by alleging a need to apply special considerations or exemptions from typical analysis. These considerations or exemptions are pushed into the argument without proper criticism. Essentially, this involves someone attempting to cite something as an exemption to a generally accepted rule, principle, etc. without justifying the exemption. This fallacious argument is one of the most used in alternative medicine and other pseudoscientific areas, since, lacking any scientific evidence, they attempt to excuse the lack of evidence not because of implausibility, but because we lack the abilities to understand their special mechanism. Often, you will here the phrase, "mainstream science just hasn't uncovered the mechanism yet."

Example
Homeopathy cannot be tested with modern science because we do not have a proper understanding of its mechanisms.

Strawman Argument
A strawman is an argument that misrepresents a position of the other side, in order to make it appear weaker than it actually is. The arguer then refutes the arguer's misrepresentation of the position, leading others to conclude that the real position has been refuted. It is an intentional misrepresentation of an opponent's position, often used in debates with unsophisticated audiences to make it appear that the opponent's arguments are more easily defeated than they are. This is a fallacy, of course, because it has done nothing to actually refute the position of the other side of the argument, nor provide any evidentiary support of either side of the argument.

Example
The pro-vaccination doctors do not care about our autistic children, so vaccines are bad.