Category Archives: Logical fallacies

Appeal to Ignorance


by Tim Harding

The scope of the Appeal to Ignorance fallacy (Argumentum ad Ignorantiam in Latin) is more limited than its title would suggest. In the specific context of this fallacy, the word ignorance represents ‘a lack of contrary evidence’ rather than a lack of education or knowledge. The fallacy title was likely coined by the philosopher John Locke in the late 17th century.

In informal logic, this fallacy asserts that a proposition is true because it has not yet been shown to be false, or a proposition is false because it has not yet been shown to be true. This represents a type of false dichotomy, in that it excludes the possibility that there may have been an insufficient investigation to determine whether the proposition is either true or false. In other words, ‘absence of evidence is not evidence of absence.’

In rhetorical debates, appeals to ignorance are sometimes used in an attempt to shift the burden of proof.  A typical example is as follows: ‘In spite of all the talk, not a single flying saucer report has been authenticated. We may assume, therefore, there are no such things as flying saucers.’ An absurd but logically equivalent example is: ‘Although NASA has shown that the surface of the moon is not made of green cheese, it has not conclusively demonstrated that the Moon’s core is not made of it; therefore, the moon’s core is made of green cheese.

This fallacy is a potential trap that empiricists need to be wary of falling into. We cannot prove the non-existence of anything, so the burden of proof lies with those who claim the existence of something, rather than those who doubt it. So, we should always remain open to the possibility of new evidence in support of a claim, even if no such evidence has ever been found.

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Five most popular fallacies of 2018

The five most popular articles on this blog during 2018, apart from the home page, were all on fallacies:

  1. Fallacies of composition and division (9,187 views).
  2. Moral equivalence (6,376 views).
  3. False equivalence (4,281 views).
  4. Zero-sum fallacy (3,547 views).
  5. Perfect solution fallacy (3,229 views).

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Why anti-vaxxers get it so wrong

By Tim Harding

The inability to accurately appraise one’s own knowledge is a cognitive bias known as the Dunning-Kruger Effect, first identified from social psychology experiments conducted in 1999. Dunning-Kruger effects occur when individuals’ lack of knowledge about a particular subject leads them to inaccurately gauge their expertise on that subject. Ignorance of one’s own ignorance can lead people who lack knowledge on a subject to think of themselves as more expert than those who are comparatively better informed.

A recent study published in the peer-reviewed journal Social Science and Medicine (and summarised in The Conversation) demonstrated that at least some anti-vaccination views are based on the Dunning-Kruger Effect.  The study found that 71 per cent of those who strongly endorse misinformation about the link between vaccines and autism feel that they know as much or more than medical experts about the causes of autism, compared to only 28 per cent who most strongly reject that misinformation.

The researchers found that nearly a third, or 30 percent, of people who think that they know more than medical experts about the causes of autism strongly support giving parents the latitude to not vaccinate their children. By contrast, 16 percent of those who do not think that they know more than medical professionals felt the same way.

The study also found that people who think they know more than medical experts are more likely to trust information about vaccines from non-expert sources, such as celebrities. These individuals are also more likely to support a strong role for non-experts in the process of making policies about vaccines and vaccination.

Whilst these recent research findings may not come as a surprise to seasoned skeptics, we now have  empirical evidence to explain why at least some anti-vaccination views are so irrational.

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‘It’s only a theory’

by Tim Harding

(An edited version of this article was published in The Skeptic magazine,
June 2018, Vol 38 No 2)

One of the most face-palming things about having a science background is when creationists or other science deniers say ‘It’s only a theory’ when dismissing a scientific theory such as evolution.  This was recently the misconception that frustrated readers the most on The New York Times – Science Facebook page.

In everyday conversation, we tend to use the word ‘theory’ to mean a hunch, a guess or tentative hypothesis, as opposed to a known fact.  But that’s not what a ‘theory’ means to scientists.

‘In science, the word theory isn’t applied lightly,’ says Kenneth R. Miller, a cell biologist at Brown University. ‘It doesn’t mean a hunch or a guess. A theory is a system of explanations that ties together a whole bunch of facts. It not only explains those facts, but predicts what you ought to find from other observations and experiments.’

Photo credit: Zohar Lazar

The word ‘proof’ is used in mathematics but not in serious science.  I don’t recall ever seeing the word ‘proof’ used in this sense in a published scientific paper.

The prevailing scientific theory is the one that best explains the facts and has not been falsified, despite experimental attempts to do so. As Richard Dawkins says ‘Gravity is a fact. Evolution is a fact. The prevailing theory of gravity is Einstein’s. The prevailing theory of evolution is Darwin’s.’  Dawkins has also invited anyone who doubts the theory of gravity to test it by jumping out of a tenth-storey window.

This conflation of two different meanings of the word ‘theory’ is an instance of the equivocation fallacy.  In logic, equivocation is an informal fallacy resulting from the use of a particular word or expression in more than one sense throughout an argument, leading to a misconception.  It is a type of ambiguity that stems from a term having two distinct meanings, not from the grammar or structure of the sentence.


Zimmer, Carl. In Science, It’s Never ‘Just a Theory’. The New York TimesApril 8, 2016.


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Cultural universals vs cultural relativism

cultural universal (also called a human universal), as discussed by Emile DurkheimGeorge MurdockClaude Lévi-StraussDonald Brown,  Steven Pinker and others, is an element, pattern, trait, or institution that is common to all human cultures worldwide. In his book Human Universals (1991), Donald Brown defines human universals as comprising “those features of culture, society, language, behavior, and psyche for which there are no known exception”, providing a list of hundreds of items he suggests as universal. Steven Pinker lists all Brown’s universals in the appendix of his book The Blank Slate.

Evolutionary psychologists hold that behaviors or traits that occur universally in all cultures are good candidates for evolutionary adaptations. Some anthropological and sociological theorists that take a cultural relativist perspective may deny the existence of cultural universals: the extent to which these universals are “cultural” in the narrow sense, or in fact biologically inherited behavior is an issue of “nature versus nurture“. The existence of cultural universals provides strong evidence against the currently fashionable notion that all human behaviours, including gender differences, are culturally determined.

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Consent to risk fallacy

A common argument against counter-terrorism measures is that more people are killed each year by road accidents than by terrorists.  Whilst this statistic may be true, it is a false analogy and a red herring argument against counter-terrorism. It also ignores the fact that counter-terrorism deters and prevents more terrorist attacks than those that are eventually carried out.

This fallacious argument can be generalised as follows: ‘More people are killed by (fill-in-the-blank) than by terrorists, so why should we worry about terrorism?’  In recent media debates, the ‘blank’ has included not only road accidents, but also deaths from falling fridges and bathtub drownings.  However, for current purposes let us assume that more people do die from road accidents than would have died from either prevented or successful terrorist attacks.

Whenever we travel in a car, almost everybody is aware that there is a small but finite risk of being injured or killed.  Yet this risk does not keep us away from cars.  We intuitively make an informal risk assessment that the level of this risk is acceptable in the circumstances.  In other words, we consent to take the risk of travelling in cars, because we decide that the low level of risk of an accident does not outweigh the benefits of car transport.

On the other hand, in western countries we do not consent to take the risk of being murdered by terrorists, unless we deliberately decide to visit a terrorist-prone area like Syria, northern Iraq or the southern Philippines.  A terrorist attack could occur anywhere in the West, so unlike the road accident analogy, there is no real choice a citizen can make to consent or not consent to the risk of a terrorist attack.

The Consent to risk fallacy omits this critical factor of choice from the equation, so the analogy between terrorism and road accidents is false.



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Travel expenses are not ‘entitlements’

‘I hate the word entitlement’
– Prime Minister Malcolm Turnbull, 13 January 2017

During the recent political scandal about MPs claiming reimbursement for non-work related travel expenses, the media has mistakenly referred to travel expenses as ‘entitlements’, thus implying that they are some sort of ‘perk‘* of office.  This usage of the word ‘entitlement’ is irrational; and any argument that the reimbursement of legitimate work-related travel expenses is a perk is fallacious. It reveals a lexicological laziness on the part of journalists who pride themselves on being wordsmiths.

All employees have the right to be reimbursed for legitimate expenses incurred as a result of doing their job. Such reimbursements are not classified as income by the ATO, and they cannot logically be regarded as a ‘perk’ of office. On the contrary, if legitimate work expenses were not reimbursed, the employee would in effect be donating money to their employer.

Where such expenses are claimed for non-work related activities, they should not be reimbursed and if they have been reimbursed in error, they need to be repaid by the recipient. In this context, the use of the word ‘entitlement’ is doubly irrational.


*Cambridge Dictionary definition: An advantage or something extra, such as money or goods, that you are given because of your job e.g. ‘A company car and a mobile phone are some of the perks that come with the job’.

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Appeal to hypocrisy

Appeal to hypocrisy (also known as Tu quoque, Latin for, ‘you also’) is an informal logical fallacy that tries to discredit the validity of the opponent’s argument by asserting the opponent’s failure to act consistently in accordance with its conclusion(s).

The Appeal to Hypocrisy fallacy follows the pattern:

  1. Person A makes claim X.
  2. Person B asserts that A’s actions or past claims are inconsistent with the truth of claim X.
  3. Conclusion: Therefore X is false.

An example would be

Peter: ‘Based on the arguments I have presented, it is evident that it is morally wrong to use animals for food or clothing.’

Bill: ‘But you are wearing a leather jacket and you have a roast beef sandwich in your hand! How can you say that using animals for food and clothing is wrong?’

This argument is a fallacy because the moral character or past actions of the opponent are generally irrelevant to the validity of the argument. It is often used as a red herring tactic and is a special case of the ad hominem fallacy, which is a category of fallacies in which a claim or argument is rejected on the basis of facts about the person presenting or supporting the claim or argument.



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No true Scotsman

No true Scotsman is a kind of informal fallacy in which one attempts to rescue a universal generalisation from counterexamples by changing the definition in an ad hoc fashion to exclude the counterexample. Rather than denying the counterexample or rejecting the original claim, this fallacy modifies the subject of the assertion to exclude the specific case or others like it by rhetoric i.e. those who perform that action are not part of our group and thus criticism of that action is not criticism of the group.

Philosophy professor Bradley Dowden explains the fallacy as an ‘ad hoc rescue’ of a refuted generalisation attempt. The following is a simplified rendition of the fallacy:

Person A: ‘No Scotsman puts sugar on his porridge.’

Person B: ‘But my uncle Angus likes sugar with his porridge.’

Person A: ‘Ah yes, but no true Scotsman puts sugar on his porridge.’

The introduction of the term is attributed to British philosopher Prof. Antony Flew, because the term originally appeared in Flew’s 1971 book An Introduction to Western Philosophy.

A practical example of this fallacy occurs when Marxists try to defend their regressive and unworkable ideology against the overwhelming evidence from the 20th century that almost every communist regime was brutally repressive; and most of them resulted in poverty for everybody except the communist party hierarchy. ‘But they weren’t true communists’ they say. Yeah, right.

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‘I’m entitled to my opinion’

(An edited version of this article was published in
“The Skeptic” Vol 37, No. 2, June 2017)

The claim ‘I’m entitled to my opinion’ or ‘I have a right to my opinion’ is a logical fallacy in which a person attempts to reject objections to their argument by claiming that they are entitled to their opinion.  This claim is usually uttered by people in disagreement when they have hit the wall in defending their point on its merits. It is a last ditch rhetorical device that attempts to rescue their position by defending their right to hold an opinion, no matter how ill-founded or wrong that opinion might be.

The claim exemplifies a red herring. The right to have an opinion is not what is in dispute. Whether one has a particular entitlement or right is irrelevant to whether one’s opinion is true or false. To assert the existence of the right is a failure to provide any justification for the content of the opinion. The claim also implies that all opinions are equal, which exemplifies the relativist fallacy.[1]

The entitlement claim would be relevant only if it guaranteed the truth of your opinions. But it can’t do that, because it is an entitlement supposedly enjoyed by everybody. And people disagree.  Two debaters are both entitled to their contradictory opinions about a given issue, but they can’t both be right. [2] So insisting that you are entitled to your opinion cannot possibly give you any logical advantage in a debate.


[1] The relativist fallacy, also known as the subjectivist fallacy, is claiming that something is true for one person but not true for someone else. The fallacy rests on the law of noncontradiction. The fallacy applies only to objective facts, or what are alleged to be objective facts, rather than to personal tastes or subjective experiences.

[2] In classical logic, the law of non-contradiction (LNC) is the second of the three classic laws of thought. It states that contradictory statements cannot both be true in the same sense at the same time, e.g. the two propositions ‘A is B’ and ‘A is not B’ are mutually exclusive.


Harding, Tim ‘Who needs to Know?’ The Skeptic magazine, September 2015, Vol 36 No 3 p.36.

Stokes, Patrick., ‘No, you’re not entitled to your opinion’. The Conversation. October 5, 2012.

Whyte, Jamie (August 9, 2004). ‘Sorry, but you are not entitled to your opinion’. The Times. News UK.


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