Tag Archives: logical fallacies

Reverse causation fallacy

Recently on the Australian “Sunrise” TV program co-presenter David Koch said: “There have only been 3000 deaths from COVID, far less than that from influenza in the same period, so we should oppose the lockdowns”.  This statement ignored the fact that prior to and during the vaccination rollout, lockdowns are likely to have prevented many thousands more deaths.

Similarly, some people argue against counter-terrorism measures on the grounds that there have been relatively few successful terrorist attacks in Australia, ignoring the fact that counter-terrorism has deterred and disrupted many more terrorist plots than those that have been carried out.

Several years ago, I was working as a regulatory consultant helping to remake sunsetting Victorian water regulations. Amongst other things, these regulations require the installation of backflow prevention devices on the customer’s water service pipe, just after the water meter. Backflow can result in contaminants being drawn into the drinking water system if the mains pressure suddenly drops as the result of a burst water main. If a customer leaves a hose running in a chlorinated swimming pool or attached to a container of “hose-on” fertiliser, weedicide or insecticide, or worse still in an industrial chemical bath, risks to public health can occur. A Treasury official asked me how many Victorians have died as a result of such backflow incidents. When I answered “none yet” he said “so what is the problem?”. This ignored the fact that backflow prevention devices have been installed for many decades, thus preventing backflow from occurring.

These examples all make the logical error of confusing cause and effect, which is also known as the reverse causation fallacy. The low numbers of cases are caused, at least in part, by the preventative measures in place – they do not demonstrate that such measures are unnecessary. Without such measures, the numbers of cases would be likely to be many times higher.

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Moral equivalence

Moral equivalence is a form of equivocation often used in political debates. It seeks to draw comparisons between different, even unrelated things, to make a point that one is just as bad as the other or just as good as the other. Drawing a moral equivalence in this way is an informal fallacy, a special case of False equivalence.

A common manifestation of this fallacy is a claim, often made for ideological motives, that both sides are equally to blame for a war or other international conflict. Historical analyses show that this is rarely the case. Wars are usually started by one side militarily attacking the other, or mass murdering non-combatants, with or without provocation from the other side.

Some specific examples of this fallacy are as follows:

  • Claiming neither side in World War II was morally superior because of the British firebombing of Dresden in Germany, or the US atomic bombings of Hiroshima and Nagasaki in Japan. This is despite the fact that Germany started the war in Europe and Japan started the war in the Pacific. Whilst the morality of the British fire bombing of Dresden is questionable, the aim of the US atomic bombings was to force Japan to surrender, without the necessity of a land invasion in which millions of people were expected to die on both sides. The purpose was to end World War II as opposed to starting it.
  • Drawing a moral equivalence between 9/11 and U.S. policy in the Middle East, thereby attempting to justify or excuse the 9/11 atrocities against innocent non-combatants.
  • Drawing a moral equivalence between the Holocaust and Israeli actions toward the Palestinians.
  • PETA drawing a moral equivalence between the consumption of meat and the Holocaust in an ad campaign.
  • The excuse that slavery in the southern United States wasn’t so bad because some slaves were treated better than workers in northern factories and company towns — or the counter-use of the same examples, that conditions during the early Industrial Revolution were not that bad because the people were at least free to choose their jobs, unlike under slavery.

An early populariser of the expression was Jeane Kirkpatrick, who was United States ambassador to the United Nations in the Reagan administration. Kirkpatrick published an article called The Myth of Moral Equivalence in 1986, which sharply criticized those who she alleged were claiming that there was ‘no moral difference’ between the Soviet Union and democratic states.[1]


[1]  Kirkpatrick, Jeane. ‘The Myth of Moral Equivalence’, Imprimis January 1986, Vol. 15, No.1.


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Common sense fallacy

by Tim Harding

The American writer H L Mencken once said “There is always a well-known solution to every human problem — neat, plausible, and wrong.” He was referring to ‘common sense’, which can be superficially plausible and sometimes right, but often wrong.

The Common Sense Fallacy (or ‘Appeal to Common Sense’) is superficially similar to the Argument from Popularity and/or  the Argument from Tradition. However, it differs from these fallacies by not necessarily relying on popularity or tradition.

Instead, common sense relies on the vague notion of ‘obviousness’, which means something like ‘what we perceive from personal experience’ or ‘what we should know without having had to learn.’ In other words, common sense is not necessarily supported by evidence or reasoning. As such, beliefs based on common sense are unreliable.  The fallacy lies in giving too much weight to common sense in drawing conclusions, at the expense of evidence and reasoning.

In some ways, scientific methods have been developed to avoid the errors that can result from common sense. For instance, common sense used to tell us that the Earth is flat and that the Sun revolves around the Earth – because that is the way things appear to us without scientific investigation.  Another example of ‘common sense’ is that the world appears to have been designed, so therefore there must have been a designer.

Einstein’s theories of relativity were initially resisted, even by the scientific community, because they defied common sense.  They seemed to belong more in the realm of science fiction than reality, until they were later verified by scientific observations.  Our modern Global Positioning System (GPS) now uses Einstein’s relativity theories.  This initial resistance may have led Einstein to later say that ”Common sense is nothing more than a deposit of prejudices laid down by the mind before you reach eighteen” .

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Confusing correlation with causation

Consider two events A and B.  Event B closely follows Event A in time.  Does this mean that Event A caused Event B?  Possibly, but not necessarily.  Both events could have been cause by a third event C, or more likely, the close timing of Events A and B is a coincidence.  So not only is causation not the only explanation, it is not even the best explanation.

Post hoc ergo propter hoc (Latin: ‘after this, therefore because of this’ – often shortened to post hoc) is a logical fallacy that states ‘Since Event B followed Event A, Event B must have been caused by Event A.’ It is subtly different from the fallacy cum hoc ergo propter hoc (‘with this, therefore because of this’), in which two things or events occur simultaneously or the chronological ordering is insignificant or unknown. These fallacies are also known as ‘False cause’.

Post hoc is a particularly tempting error because temporal sequence appears to be integral to causality.  Indeed, if Event A did cause Event B, Event B would probably occur soon after Event A in time.  But the reverse connection is not necessarily true – temporal correlation does not imply causality.  The fallacy lies in coming to a conclusion based solely on the order of events, rather than taking into account other factors that might rule out the connection.

The form of the post hoc fallacy can be expressed as follows:

Premise: A occurred, then B occurred.

Conclusion: Therefore, A caused B.

The following is a simple example: ‘The rooster crows immediately before sunrise, therefore the rooster causes the sun to rise’.  This conclusion is false, not just we happen to know that it is factually incorrect, but because the argument is fallacious.

When B is undesirable, this fallacy is often committed in reverse: Avoiding A will prevent B.  This is the basis of many superstitious beliefs, such as bad luck associated with Friday the 13th or walking under ladders.

An example of the cum hoc fallacy is as follows.  Sleeping with one’s shoes on (A) is strongly correlated with waking up with a headache (B). Therefore, sleeping with one’s shoes on causes headache.  A more plausible explanation is that both are caused by a third factor (C), in this case going to bed drunk, which thereby gives rise to a correlation between A and B.  So the conclusion is false.

Another example, is that ice-cream sales are correlated with the level of house burglaries during warmer weather when more people are on holidays (vacation). But ice-cream doesn’t cause burglaries, nor vice versa.


Source: Wikimedia Commons

On the other hand, if A is often correlated with B, then although we still can’t logically conclude that A causes B (or vice versa), such a causal link may be a hypothesis worth testing via properly designed scientific experiments.

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Argumentum ad Monsantium

by BRIAN DUNNING, Nov 08 2012

It’s my favorite new logical fallacy, the “Appeal to Monsanto”, the world’s largest producer of biotech agriculture seeds. This is the logic that compels many anti-GMO activists to reply to any argument in support of biotech crops with “So you love Monsanto?”

It’s so wonderful because it combines many other logical fallacies into one, and is thus a great time saver. For example:

  • It poisons the well (cloaks a viewpoint with negative weasel words) by associating the scary, evil word Monsanto.
  • It’s a non-sequitur (a logical association that does not follow). IF (a) THEREFORE (b). IF (genes can be used to confer traits such as drought resistance) THEREFORE (I love Monsanto).
  • It’s a straw man (misrepresenting what I said into something that’s easy to argue against). If I had actually said “I love Monsanto”, then plenty of rational arguments are available to show that’s a bad idea.
  • It’s an ad hominem attack on my argument (the argument is wrong because of who the person is that made it). Whatever I said about biotech must be wrong since “I love Monsanto”.
  • It’s a red herring (an irrelevancy to distract from the subject under discussion). Monsanto does not necessarily have anything to do with any given science-based discussion of the merits of what can and should be done with direct genetic manipulation.

Also, the Appeal to Monsanto comes in many different forms. Here are some Appeals to Monsanto from my first episode on organic food (skep.us/4019), which did not mention Monsanto at all:

Brian is basically an uninformed apologist for big agro-business. I would not be surprised if he is pulling a salary from Monsanto or Cargill.
G William Shea, 2/2/2008

well, actually [Brian] is very very very uninformed on a lot of subjects, including the scientific method! anyway, another one to see about GM and a real eye-opener in my eye 😉 “The world according to Monsanto”
Pindar, 2/10/2009

check out the documentary, “The World According to Monsanto” you can find it on the popular video sites out there for free.
Justan, 2/24/2009

But the problem is not to justify the status quo; the problem is dealing with the implications of monoculture, the ownership of biological processes, the desertification or sterility of fertile land, the multifarious effects of carbon-intensive cultivation, and the implications of unfair government subsidies for certain crops (which hurt the farmer, especially the corn farmer, the most, and help Cargill, Coca Cola, and Monsanto, the most).
Jay, 2/24/2009

I will gladly pay more for organic food if it means I’m not a lab rat for Monsanto.
Erin, 10/2/2009

Its not a matter of IF but WHEN it hurts [Brian] and his family will something be done. I’d try to see his point of view but I just cant put my head that far up my A**! I wonder if he is being paid by Monsanto.
Paul, 2/24/2010

i dont know what you are trying to accomplish by this blog but you seem to have all ur facts skewed. who do you work for monsanto?
MATT, 5/2/2010

Claiming that organic foods are less healthy is the most obvious farce in your article as well as your blind belief that pesticides and herbicides are healthy and biodegradable.  They might biodegrade, but not within a million years.  If you are a “skeptic” then why would you believe monsanto funded studies.
Tyler K., 12/12/2010

You don’t work for someone like Monsanto do you?
Phi, 4/6/2011

I have heard that often farmers who buy genetically modified seeds enter into a contract with Monsanto and are only allowed to use Roundup products.
J.O., 9/20/2011

If genetically modified foods are that much better than why has just recently been articles about the fact that the corn that Monsanto has produced having problems with the very pests that it was modified to not be affected by.
Steve, 10/21/2011

“To feed a growing population …” This is an argument used by corporations such as Monsanto.
Eric B, 10/27/2011

Couldn’t have written a more obviously emotionally biased article if Monsanto covered your expenses.
Samuel, 7/18/2012

Monsanto is owned by the zionist jews
AmericanPower, 9/9/2012

The Appeal to Monsanto was also employed in response to my episode ondetoxification (http://skep.us/4083) did not mention Monsanto at all:

Cam, I like how you say [Brian] is promoting “diet” and “water” as if he has some sort of patent on fruits and vegetables (like GE corn from Monsanto) and water which can only be bought from him.
Joe Shmoe, 1/25/2011

Even my episode on genetically modified organisms (http://skep.us/4112) did not mention Monsanto at all, as I was trying to stick with the science and avoid readers’ obvious ideological complications:

My major concern is a legal concern with such giants as Monsanto.
Justin Zimmer, 2/15/2012

A must see, The World according to Monsanto” on you tube.  A bit unsettling and disheartening.
Betty Bate, 10/13/2012

An acquaintance of mine who works with a scientific testing company has heard numerous first-hand reports of Monsanto’s threatening to stop funding university agriculture departments [i.e., withhold grant money] if they did any health/safety testing on GMO technology.
John, 10/18/2012

My episode on aspartame (http://skep.us/4127) did not mention Monsanto at all, mainly because the two have nothing whatsoever to do with each other. Yet:

Aspartame is poison period. It’s made by the biggest bunch of criminals in the world. Monsanto is determined to rule the world and might be. I get Gout as soon as I use and Aspartame.
Dean Slater, 8/27/2009

Even my episode on high fructose corn syrup (http://skep.us/4157), which was basically a chemical discussion and did not mention Monsanto, came down to hitting me with the Appeal to Monsanto:

You totally miss the point, HFC is made with GMO corn and is helping to eliminate biodiversity. Not to mention the downright evil business practices of Monsanto et al.
Mark, 3/24/2011

My episode comparing organic vs. conventional agriculture (http://skep.us/4166) did not mention Monsanto at all, as it was about the comparative sciences:

I couldn’t afford organic food for the life of me. But what about good old Round-Up Ready crops like Soy and Corn? Monsanto is taking over the bloody world, and they are going to soon OWN our food supply and all patents to it.
Kimberly, 8/12/2009

I wonder what you would think about our food supply if you had to shut all the windows in your home and flee the area several times a year while the crops are being sprayed with round up and other poisons.  I wonder if you would appreciate Monsanto and their schemes to dominate every farmer you know.
kadie, 11/21/2009

we’re all gonna die if this path is follwed much longer, but thankfully many people unlike yourself are waking up to the REALITY of chemical agriculture and not just stupidly DEFENDING it for no reason like you are. thanks for nothing, and thank goodness not everyone blindly defends monsanto and big AG like you and your fellow skeptoids.
mike, 12/17/2010

My episode on morgellons disease (http://skep.us/4206) had nothing remotely to do with Monsanto. Yet:

Who pays you to be such an idiot? Monsanto?
Colleen, 9/25/2012

My episode on the things we eat (http://skep.us/4216) was a discussion of the basic building blocks of nutrition and so, naturally, did not mention Monsanto:

The vast majority of our food (whether plant or animal) comes from factory farms. This is not healthy and it’s a business model that cannot sustain itself. Thanks to WalMart, Monsanto, and other mega-giants for that debilitating trend!
Joe Boudreault, 7/30/2010

Somehow even my episode on the Bilderberg Group (http://skep.us/4225) conspiracy theory fell prey to the dreaded Appeal to Monsanto:

This problem started in 1930 with President FDR signing a treaty allowing the taking of a limited amount of human specimens for research purposes. In exchange the Grey’s gave us the perfected “sonar technology” in exchange. Since that time they have taken over our Dem & Rep parties. They have managed to infiltrate our manufacturing facilities, have bought out Proctor & Gamble and created the Monsanto Company.
David Kaas, 6/19/2011

There was a listener feedback (http://skep.us/4232) episode that made one mention of aspartame (which has nothing to do with Monsanto) and yet got this:

We live in a messed up world…we all better open our eyes and make a stand…because our health is in the hands of Monsanto and other giants…maybe we should look at Bill S510 but I’m sure everyone here is in favorite of that one lol
BJ, 11/18/2010

It would never have occurred to me that the Appeal to Monsanto can even be used to justify the antisemitism of the Zionist Conspiracy (http://skep.us/4271), but so it can:

Brian, your opening statement on this subject says that “anti semitisim is institutionalized by world super powers” ? ??   Brian you are blind,  what would you call Aipac?, ADL? IDF? Mossad? Monsanto? ect ect (all Zionist owned.)
Jim White, 10/13/2012

And finally, the Appeal to Monsanto can even be used to stain the reputation of those who are already stained, like Joe Mercola who was featured in the episode on the 10 worst anti-science websites (http://skep.us/4283):

Have you heard about Mercola’s link to an Indian company that makes pesticides, fertilizers, and bisphenol A and invests in Monsanto seed products? 😉
ejwillingham, 11/8/2011

So, blog commenters, keep this tool handy. The Appeal to Monsanto can apparently be used anytime, anywhere, to argue anything, and it need have no relationship to biotech at all. Enjoy.

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The Red Herring Fallacy

The idiom ‘red herring’ is used to refer to something that misleads or distracts from the relevant or important issue.  The expression is mainly used to assert that an argument is not relevant to the issue being discussed.

A red herring fallacy is an error in logic where a proposition is, or is intended to be, misleading in order to make irrelevant or false inferences. It includes any logical inference based on fake arguments, intended to replace the lack of real arguments or to replace implicitly the subject of the discussion.  In this way, a red herring is as much a debating tactic as it is a logical fallacy.  It is a fallacy of distraction, and is committed when a listener attempts to divert an arguer from his argument by introducing another topic.  Such arguments have the following form:

Topic A is under discussion.

Topic B is introduced under the guise of being relevant to topic A (when topic B is actually not relevant to topic A).

Topic A is abandoned.

This sort of reasoning is fallacious because merely changing the topic of discussion hardly counts as an argument against a claim.

For instance, ‘I’m entitled to my opinion’ or ‘I have a right to my opinion’ is a common declaration in rhetoric or debate that can be made at some point in a discussion. 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 assert any justification for the opinion.

As an informal fallacy, the red herring falls into a broad class of relevance fallacies. Unlike the strawman fallacy, which is premised on a distortion of the other party’s position, the red herring is a seemingly plausible, though ultimately irrelevant, diversionary tactic.  According to the Oxford English Dictionary, a red herring may be intentional or unintentional – it does not necessarily mean a conscious intent to mislead.

Source: Wikimedia Commons

Source: Wikimedia Commons

Conventional wisdom has long supposed the origin of the idiom ‘red herring’ to be the use of a kipper (a strong-smelling smoked fish) to train hounds to follow a scent, or to divert them from the correct route when hunting; however, modern linguistic research suggests that the term was probably invented in 1807 by English polemicist William Cobbett, referring to one occasion on which he had supposedly used a kipper to divert hounds from chasing a hare, and was never an actual practice of hunters.  The phrase was later borrowed to provide a formal name for the logical fallacy and associated literary device.

Although Cobbett most famously mentioned it, he was not the first to consider red herring for scenting hounds; an earlier reference occurs in the pamphlet ‘Nashe’s Lenten Stuffe’, published in 1599 by the Elizabethan writer Thomas Nashe, in which he says ‘Next, to draw on hounds to a scent, to a red herring skin there is nothing comparable’.

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Fallacies of composition and division

The Fallacy of Composition arises when one infers that something is true of the whole from the fact that it is true of some part of the whole.  Conversely, the Fallacy of Division occurs when one infers that something true for the whole must also be true of all or some of its parts.  Both fallacies were described by Aristotle in Sophistical Refutations.

Fallacy of composition

The logical form of the Fallacy of Composition is:

     Premise 1: A is part of B

     Premise 2: A has property X

     Conclusion: Therefore, B has property X.

Two examples of this fallacy are:

  • If someone stands up out of his seat at a baseball game, he can see better.  Therefore, if everyone stands up they can all see better.

  • If a runner runs faster, she can win the race.  Therefore if all the runners run faster, they can all win the race.

Athletic competitions are examples of zero-sum games, wherein the winner wins by preventing all other competitors from winning.

Another example of this fallacy is:

Sodium (Na) and Chlorine (Cl) are both dangerous to humans. Therefore any combination of sodium and chlorine, such as common table salt (NaCl) will be dangerous to humans.

This fallacy is often confused with the fallacy of faulty generalisation, in which an unwarranted inference is made from a statement about a sample to a statement about the population from which it is drawn.

In economics, the Paradox of Thrift is a notable fallacy of composition that is central to Keynesian economics.  Division of labour is another economic example, in which overall productivity can greatly increase when individual workers specialize in doing different jobs.

In a Tragedy of the Commons, an individual can profit by consuming a larger share of a common, shared resource such as fish from the sea; but if too many individuals seek to consume more, they can destroy the resource.

In the Free Rider Problem, an individual can benefit by failing to pay when consuming a share of a public good; but if there are too many such ‘free riders’, eventually there will be no ‘ride’ for anyone.

Fallacy of division

The Fallacy of Division is the converse of the Fallacy of Composition.  The logical form of the Fallacy of Division is:

      Premise 1: A is part of B

      Premise 2: B has property X

      Conclusion: Therefore, A has property X.

An example the fallacy of division is:

A Boeing 747 can fly unaided across the ocean.

A Boeing 747 has jet engines.

Therefore, one of its jet engines can fly unaided across the ocean.

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The Slippery Slope

by Tim Harding

A slippery slope argument may or may not be a fallacy, depending on whether the argument is logical.  The argument typically states that a relatively small first step will inevitably lead to a chain of related events culminating in some significant consequence, much like an object given a small push over the edge of a slope will slide all the way to the bottom.  


A slippery slope argument has the following form:

Premise: Event X has occurred (or will or might occur).

Conclusion: Therefore consequence Y will inevitably happen.

The strength of such an argument depends on whether or not one can demonstrate a chain of cause and effect leading to the significant consequence.  If no such chain can be demonstrated, the argument becomes a fallacy. This is especially so in cases in which there is a significant number of steps or gradations between one event and another, which increases the probability of the chain of cause and effect being broken. On the other hand, if the chain of cause and effect can be adequately demonstrated to be unbroken, the argument is logical.

The fallacious form of this argument has traditionally been called The Camel’s Nose, because of the image of a sheik whose camel sticks its nose into his tent on a cold night.  The idea is that the sheik is afraid to let the camel put its nose into the tent because once the beast puts in its nose, it will inevitably put in its head, and then its neck, and eventually its whole body.[1] However, this sort of thinking does not allow for any possibility of stopping the process. It simply assumes that, once the nose is in, the rest must follow — that the sheik can’t stop the progression once it has begun — and thus the process is inevitable.[2]

Camel's Nose

For instance, if one were to argue,

“If we allow the government to infringe upon our right to privacy on the Internet, it will then feel free to infringe upon our privacy on the telephone. After that, FBI agents will be reading our mail. Then they will be placing cameras in our houses. We must not let any governmental agency interfere with our Internet communications, or privacy will completely vanish in the United States.”

Such thinking is fallacious; no logical proof has been provided yet that infringement in one area will necessarily lead to infringement in another, no more than a person buying a single can of Coca-Cola in a grocery store would indicate the person will inevitably go on to buy every item available in the store, helpless to stop herself.[2]

A currently topical example is that one of the arguments against same-sex marriage is that it will lead to a demand for the adoption of children by same-sex married couples.  It is argued that such a demand will be difficult to resist under anti-discrimination legislation; and so the way to prevent such adoptions is to resist same-sex marriage.  There are arguments for and against the need for children to have a relationship with both and father and a mother, but these arguments are not critical to whether or not the slippery slope argument is fallacious.  If there will be no irresistable demand for the adoption of children by same-sex married couples, then the slippery slope argument is clearly fallacious in this case.

Notes and references

[1] The Camel’s Nose fallacy is sometimes described as being based on an old Arabian fable or proverb; however this provenance is doubtful. It is more likely to be a Victorian English invention.

[2] Makethestand.com Learning to Reason Clearly by Understanding Logical Fallacies. Posted 19/7/07. Viewed 9/3/14.

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Sunk cost fallacy

by Tim Harding

In economics and business decision-making, a sunk cost is a retrospective (past) cost that has already been incurred and cannot be recovered. Sunk costs are sometimes contrasted with prospective costs, which are future costs that may be incurred or changed if an action is taken.

In traditional microeconomic theory, only prospective (future) costs are relevant to an investment decision. Traditional economics proposes that economic actors should not let sunk costs influence their decisions. Doing so would not be rationally assessing a decision exclusively on its own merits.

On the other hand, evidence from behavioral economics suggests this theory fails to predict real-world behavior. Sunk costs do, in fact, influence actors’ decisions because humans are prone to loss aversion and framing effects. In light of such cognitive quirks, it is unsurprising that people frequently fail to behave in ways that economists deem  rational.

Sunk costs should not affect the rational decision-maker’s best choice. However, until a decision-maker irreversibly commits resources, the prospective cost is an avoidable future cost and is properly included in any decision-making processes. For example, if one is considering preordering movie tickets, but has not actually purchased them yet, the cost remains avoidable. If the price of the tickets rises to an amount that requires him to pay more than the value he places on them, he should figure the change in prospective cost into the decision-making and re-evaluate his decision.

Many people have strong misgivings about ‘wasting’ resources (loss aversion). Continuing with the movie ticket analogy, after purchasing a non-refundable movie ticket, many people, for example, would feel obliged to go to the movie despite not really wanting to, because doing otherwise would be wasting the ticket price – they feel they have passed the point of no return. Similarly, some people will not walk out of a movie they dislike, because they do not want to ‘waste’ the money they have already paid and cannot recover i.e. the sunk cost. This is despite the fact that if they walk out of the movie, they could spend the time doing something else that they much prefer.

Another common instance of this behaviour is the reluctance to sell underperforming company shares (stocks) for fear of wasting one’s original investment; when it would make better sense to sell the shares and use the money to buy some other shares that are more likely to perform better.

This  behaviour referred to as the sunk cost fallacy. Economists would label this behavior ‘irrational‘: it is inefficient because it misallocates resources by depending on information that is irrelevant to the decision being made. Colloquially, this is known as ‘throwing good money after bad’. It could also be described as a form of preference failure i.e. not acting in one’s own best interests.

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Argument from consequences

The Argument from Consequences, also known as (‘Appeal to Consequences’) or argumentum ad consequentiam [1], is a fallacious argument that concludes that a belief is either true or false based on whether the belief leads to desirable or undesirable consequences.  Such arguments are closely related to the fallacies of appeal to emotion and wishful thinking.  They generally have one of two forms:

Positive form

Premise 1: If P, then Q will occur.

Premise 2: Q is desirable.

Conclusion: Therefore, P is true.


  • Humans must be able to travel faster than light, because that will be necessary for interstellar space travel.
  • I believe in an afterlife, because I want to exist forever.

Negative form

Premise 1: If P, then Q will occur.

Premise 2: Q is undesirable.

Conclusion: Therefore, P is false.


  • Free will must exist: if it didn’t, we would all be machines.” (This is also a false dilemma.)
  • Evolution must be false: if it were true then human beings would be no better than animals.
  • God must exist; if He did not, then people would have no reason to be good and life would have no meaning.

Such arguments are invalid because the conclusion does not logically follow from the premises.  The desirability of a consequence does not make a conclusion true; nor does the undesirability of a consequence make a conclusion false.  Moreover, in categorizing consequences as either desirable or undesirable, such arguments inherently contain subjective points of view.

There are two types of cogent argument with which this fallacy is easily confused:

  1. When an argument is about a proposition, it is reasonable to assess the truth-value (whether it is true or false) of any logical consequences of the proposition.  Logical consequences should not be confused with causal consequences; and truth or falsity should not be confused with goodness or badness.
  2. When an argument concerns a policy or plan of action—instead of a proposition—then it is reasonable to consider the consequences of acting on it, because policies and plans are good or bad rather than true or false.


[1] Latin for ‘argument to the consequences’

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