Tag Archives: rationality

What is logic?

The word ‘logic‘ is not easy to define, because it has slightly different meanings in various applications ranging from philosophy, to mathematics to computer science. In philosophy, logic’s main concern is with the validity or cogency of arguments. The essential difference between informal logic and formal logic is that informal logic uses natural language, whereas formal logic (also known as symbolic logic) is more complex and uses mathematical symbols to overcome the frequent ambiguity or imprecision of natural language. Reason is the application of logic to actual premises, with a view to drawing valid or sound conclusions. Logic is the rules to be followed, independently of particular premises, or in other words using abstract premises designated by letters such as P and Q.

So what is an argument? In everyday life, we use the word ‘argument’ to mean a verbal dispute or disagreement (which is actually a clash between two or more arguments put forward by different people). This is not the way this word is usually used in philosophical logic, where arguments are those statements a person makes in the attempt to convince someone of something, or present reasons for accepting a given conclusion. In this sense, an argument consist of statements or propositions, called its premises, from which a conclusion is claimed to follow (in the case of a deductive argument) or be inferred (in the case of an inductive argument). Deductive conclusions usually begin with a word like ‘therefore’, ‘thus’, ‘so’ or ‘it follows that’.

A good argument is one that has two virtues: good form and all true premises. Arguments can be either deductiveinductive  or abductive. A deductive argument with valid form and true premises is said to be sound. An inductive argument based on strong evidence is said to be cogent. The term ‘good argument’ covers all three of these types of arguments.

Deductive arguments

A valid argument is a deductive argument where the conclusion necessarily follows from the premises, because of the logical structure of the argument. That is, if the premises are true, then the conclusion must also be true. Conversely, an invalid argument is one where the conclusion does not logically follow from the premises. However, the validity or invalidity of arguments must be clearly distinguished from the truth or falsity of its premises. It is possible for the conclusion of a valid argument to be true, even though one or more of its premises are false. For example, consider the following argument:

Premise 1: Napoleon was German
Premise 2: All Germans are Europeans
Conclusion: Therefore, Napoleon was European

The conclusion that Napoleon was European is true, even though Premise 1 is false. This argument is valid because of its logical structure, not because its premises and conclusion are all true (which they are not). Even if the premises and conclusion were all true, it wouldn’t necessarily mean that the argument was valid. If an argument has true premises and its form is valid, then its conclusion must be true.

Deductive logic is essentially about consistency. The rules of logic are not arbitrary, like the rules for a game of chess. They exist to avoid internal contradictions within an argument. For example, if we have an argument with the following premises:

Premise 1: Napoleon was either German or French
Premise 2: Napoleon was not German

The conclusion cannot logically be “Therefore, Napoleon was German” because that would directly contradict Premise 2. So the logical conclusion can only be: “Therefore, Napoleon was French”, not because we know that it happens to be true, but because it is the only possible conclusion if both the premises are true. This is admittedly a simple and self-evident example, but similar reasoning applies to more complex arguments where the rules of logic are not so self-evident. In summary, the rules of logic exist because breaking the rules would entail internal contradictions within the argument.

Inductive arguments

An inductive argument is one where the premises seek to supply strong evidence for (not absolute proof of) the truth of the conclusion. While the conclusion of a sound deductive argument is supposed to be certain, the conclusion of a cogent inductive argument is supposed to be probable, based upon the evidence given. An example of an inductive argument is: 

Premise 1: Almost all people are taller than 26 inches
Premise 2: George is a person
Conclusion: Therefore, George is almost certainly taller than 26 inches

Whilst an inductive argument based on strong evidence can be cogent, there is some dispute amongst philosophers as to the reliability of induction as a scientific method. For example, by the problem of induction, no number of confirming observations can verify a universal generalization, such as ‘All swans are white’, yet it is logically possible to falsify it by observing a single black swan.

Abductive arguments

Abduction may be described as an “inference to the best explanation”, and whilst not as reliable as deduction or induction, it can still be a useful form of reasoning. For example, a typical abductive reasoning process used by doctors in diagnosis might be: “this set of symptoms could be caused by illnesses X, Y or Z. If I ask some more questions or conduct some tests I can rule out X and Y, so it must be Z.

Incidentally, the doctor is the one who is doing the abduction here, not the patient. By accepting the doctor’s diagnosis, the patient is using inductive reasoning that the doctor has a sufficiently high probability of being right that it is rational to accept the diagnosis. This is actually an acceptable form of the Argument from Authority (only the deductive form is fallacious).

References:

Hodges, W. (1977) Logic – an introduction to elementary logic (2nd ed. 2001) Penguin, London.
Lemmon, E.J. (1987) Beginning Logic. Hackett Publishing Company, Indianapolis.

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Argument from authority

by Tim Harding

The Argument from Authority is often misunderstood to be a fallacy in all cases, when this is not necessarily so. The argument becomes a fallacy only when used deductively, or where there is insufficient inductive strength to support the conclusion of the argument.

The most general form of the deductive fallacy is:

Premise 1: Source A says that statement p is true.
Premise 2: Source A is authoritative.
Conclusion: Therefore, statement p is true.

Even when the source is authoritative, this argument is still deductively invalid because the premises can be true, and the conclusion false (i.e. an authoritative claim can turn out to be false).[1] This fallacy is known as ‘Appeal to Authority’.

The fallacy is compounded when the source is not an authority on the relevant subject matter. This is known as Argument from false or misleading authority.

Although reliable authorities are correct in judgments related to their area of expertise more often than laypersons, they can occasionally come to the wrong judgments through error, bias or dishonesty. Thus, the argument from authority is at best a probabilistic inductive argument rather than a deductive  argument for establishing facts with certainty. Nevertheless, the probability sometimes can be very high – enough to qualify as a convincing cogent argument. For example, astrophysicists tell us that black holes exist. The rest of us are in no position to either verify or refute this claim. It is rational to accept the claim as being true, unless and until the claim is shown to be false by future astrophysicists (the first of whom would probably win a Nobel Prize for doing so). An alternative explanation that astrophysicists are engaged in a worldwide conspiracy to deceive us all would be implausible and irrational.

“…if an overwhelming majority of experts say something is true, then any sensible non-expert should assume that they are probably right.” [2]

Thus there is no fallacy entailed in arguing that the advice of an expert in his or her field should be accepted as true, at least for the time being, unless and until it is effectively refuted. A fallacy only arises when it is claimed or implied that the expert is infallible and that therefore his or her advice must be true as a deductive argument, rather than as a matter of probability.  Criticisms of cogent arguments from authority[3] can actually be a rejection of expertise, which is a fallacy of its own.

The Argument from Authority is sometimes mistakenly confused with the citation of references, when done to provide published evidence in support of the point the advocate is trying to make. In these cases, the advocate is not just appealing to the authority of the author, but providing the source of evidence so that readers can check the evidence themselves if they wish. Such citations of evidence are not only acceptable reasoning, but are necessary to avoid plagiarism.

Expert opinion can also constitute evidence and is often accepted as such by the courts.  For example, if you describe your symptoms to your doctor and he or she provides an opinion that you have a certain illness, that opinion is evidence that you have that illness. It is not necessary for your doctor to cite references when giving you his or her expert opinion, let alone convince you with a cogent argument. In some cases, expert opinion can carry sufficient inductive strength on its own.


[1] If the premises can be true, but the conclusion can be false, then the argument is logically invalid.

[2] Lynas, Mark (29 April 2013) Time to call out the anti-GMO conspiracy theory.

[3] An inductive argument based on strong evidence is said to be cogent.

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Three more fallacies of relevance

by Tim Harding

Fallacies are patterns of reasoning that are logically incorrect.  They apply to arguments rather than isolated statements or propositions.  Arguments are logically valid or invalid, whereas propositions are true or false. The fallacies of relevance, for example, clearly fail to provide adequate reason for believing the truth of their conclusions.  Although they are often used in attempts to persuade people by non-logical means, only the unwary, the predisposed, and the gullible are apt to be fooled by their illegitimate appeals.  Many of them were identified by medieval and renaissance logicians, some of whose Latin names for them have passed into common use.  It’s worthwhile to consider the structure, offer an example, and point out the invalidity of each of them in turn. [i]

I have previously talked here at the Mordi Skeptics about three fallacies of relevance:

  • Appeal to Popularity (argumentum ad popularum)
  • Appeal to Authority (argumentum ad verecundiam)
  • Argument from Personal Abuse (argumentum ad hominem)

I would now like to briefly talk about three more fallacies of relevance:

Appeal to Pity (argumentum ad misericordiam)

An Appeal to Pity tries to win acceptance by pointing out the unfortunate consequences that will otherwise fall upon the speaker and others, for whom we would then feel sorry.

P1: I am a single parent, solely responsible for the financial support of my children.

P2: If you give me this traffic ticket, I will lose my licence and be unable to drive to work.

P3: If I cannot work, my children and I will become homeless and may starve to death.

C: Therefore, you should not give me this traffic ticket.

The conclusion may be false (that is, perhaps I should be given the ticket) even if the premises are all true, so the argument is fallacious.

Appeal to Force
(argumentum ad baculum)

Turning this on its head, in the Appeal to Force, someone in a position of power threatens to bring down unfortunate consequences upon anyone who dares to disagree with a proffered proposition.  Although it is rarely developed so explicitly, a fallacy of this type might propose:

P1: If you do not agree with the Government’s position, we will cut funding for your scientific research.

P2: The Government’s position is that cattle grazing in alpine national parks reduces bushfire risk.

C: Therefore, cattle grazing in alpine national parks reduces bushfire risk.

Again, it should be clear that even if all of the premises were true, the conclusion could nevertheless be false.  Since that is possible, arguments of this form are plainly invalid.  While this might be an effective way to get you to agree (or at least to pretend to agree) with the Government’s position,[ii] it offers no grounds for believing it to be true.

Guilt by association (a type of ad hominem argument)

Guilt by Association relies upon emotively charged language to arouse feelings and prejudices that may lead an audience to accept its conclusion:

P1: As all clear-thinking residents of our fine state have already realized, opposition to cattle grazing in alpine national parks is nothing but the dangerous deluded dingo of greenie anti-farming propaganda cleverly disguised in the harmless sheep’s clothing of science.

C: Therefore, banning cattle grazing in alpine national parks is bad public policy.

The problem here is that although the flowery language of the premise might arouse strong feelings in many members of its intended audience, the widespread occurrence of those feelings has nothing to do with the truth of the conclusion.


[i] Most of the information on these pages has come from http://www.philosophypages.com/lg/e06a.htm, although I have devised some of my own examples of more local relevance.

[ii] Of course, public servants are required to implement lawful Government policy whether they agree with it or not; but scientists are supposed to provide independent scientific advice.

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Reasoning

Rationality may be defined as as the quality of being consistent with or using reason, which is further defined as the mental ability to draw inferences or conclusions from premises (the ‘if – then’ connection). The application of reason is known as reasoning; the main categories of which are deductive and inductive reasoning. A deductive argument with valid form and true premises is said to be sound. An inductive argument based on strong evidence is said to be cogent. It is rational to accept the conclusions of arguments that are sound or cogent, unless and until they are effectively refuted.

A fallacy is an error of reasoning resulting in a misconception or false conclusion. A fallacious argument can be deductively invalid or one that has insufficient inductive strength. A deductively invalid argument is one where the conclusion does not logically follow from the premises. That is , the conclusion can be false even if the premises are true. An example of an inductively invalid argument is a conclusion that smoking does not cause cancer based on the anecdotal evidence of only one healthy smoker.

By accident or design, fallacies may exploit emotional triggers in the listener (e.g. appeal to emotion), or take advantage of social relationships between people (e.g. argument from authority). By definition, a belief arising from a logical fallacy is contrary to reason and is therefore irrational, even though a small number of such beliefs might possibly be true by coincidence.

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What is rationality?

(Paper presented by Tim Harding at Mordi Skeptics meetup, 1 February 2011. An edited version was published in The Skeptic magazine, Vol. 36 No. 4, December 2016)

What do we skeptics mean when we say that a belief is irrational?  How do we define rationality and irrationality?  Are there any objective tests of an irrational belief?

First, some definitions.  Most dictionaries define rationality as the state or quality of being rational.  Not a lot of help.  So what does it mean to be rational? Once again, most dictionaries define rational as being consistent with or based on or using reason,[1] which is further defined as the mental ability to draw inferences or conclusions from assumptions or premises (the ‘if – then’ connection).  The application of reason is known as reasoning; the main categories of which are deductive and inductive reasoning.[2]

Reason is thought by rationalists to be more reliable in determining what is true; in contrast to reliance on other factors such as authority, tradition, instinct, intuition, emotion, mysticism, superstition, faith or arbitrary choice (e.g. flipping a coin).  For example, we rationally determine the balance in our cheque book (between bank statements) by adding up the credits and subtracting the debits and bank fees.  An irrational way of doing it would be to pick a number at random – not very reliable, and any correct answer would be a mere coincidence, rather than the product of reasoning.

The ancient Greeks thought that rationality distinguishes humans from other animals.  ‘Man is a rational animal’ as Aristotle said.[3]  However, this distinction is becoming blurred by recent research indicating that other primate species such as chimpanzees can show a limited use of reason and therefore a degree of rationality.

The word rational can be used in several different contexts; for example rational behaviour (psychology), rational or optimal decision (economics); a rational process (science), and rational belief (philosophy).  However, it is not the purpose of this paper to discuss all uses of rationality – only those relevant to our use, that is, skepticism.

I would suggest that the context most relevant to skepticism (which could be described as a form of applied philosophy) is that of rational belief, because we skeptics often criticise the beliefs of paranormals, quacks, cults and pseudo-sciences on the grounds that they are irrational (which, of course, is the antonym of rational).[4]  However, the scientific context of a ‘rational process’ is also relevant to skepticism; and I will say more about this later.

In my view, the relevance of rational belief to skepticism is that we use it as a filter to determine what we should be skeptical about.  We skeptics are not necessarily skeptical of everything.  We believe what it is rational to believe, and we are skeptical of beliefs that are known to be or appear to be irrational.  That is why I think it is important for skeptics to clarify and understand the nature of rational belief.

Harvard philosophy professor Robert Nozick has proposed two criteria for rational belief:

  1. support by reasons that make the belief credible; and
  2. generation by a process that reliably produces true beliefs.[5]

Two thought experiments

I would now like to try a couple of little thought experiments.

Firstly, imagine if you will a primitive tribe in the remote mountains of New Guinea.  The chief of this tribe needs to predict whether or not it is going to rain tomorrow[6] so he can decide whether the men will go hunting or not.  So he consults the local witch doctor, who according to long tradition slaughters a chicken and examines the configuration of the dead chicken’s entrails.  Using this information, the local witch doctor then predicts that will not rain tomorrow.  Is this a rational belief?

In terms of Nozick’s criteria, we would probably say that this belief is irrational because it is neither supported by reasons that make the belief credible, nor is it generated by a process that reliably produces true beliefs.

But what if this local witch doctor’s predictions, using the chicken entrail process, have always been right?  In that case, it could be argued that the process meets Nozick’s criterion No. 2.  It could also be argued that because the New Guinea tribe have no school education, and believe that rain and the configuration of a chicken’s entrails are caused by the same spirit, that the reasons for the witch doctor’s predictions are credible to them.  Does this alter our assessment of the rationality of this belief?  Perhaps it does.

What if exactly the same process is used by a hippie commune in Nimbin, where hippies have had the benefit of a school education and therefore should be aware that there is no credible causal connection between the incidence of rain and the configuration of a chicken’s entrails.  Do these different circumstances alter our assessment of whether the belief is rational?  Perhaps they do again.

Secondly, until early December 2010, it was believed by the scientific community (and published in reputable peer-reviewed scientific journals) that the element arsenic is toxic to all life on Earth in even very small concentrations.[7]  However, NASA-supported researchers have discovered the first known microorganism on Earth able to thrive and reproduce using arsenic.  The microorganism, which lives in California’s Mono Lake, substitutes arsenic for phosphorus in some of its cellular components.[8]  Prior to this announcement by NASA, was it rational to believe that arsenic is toxic to all life on Earth in even very small concentrations?  In terms of Nozick’s criteria, the answer would be ‘yes’, even though we now know that belief was false.  Was it rational to hold this belief after the NASA announcement?  Given that the NASA scientific announcement is credible and was generated by reliable scientific processes, our answer would be ‘no’.

By these two thought experiments, I have tried to show how a rational process can lead to a belief which may be rational in certain contexts or circumstances and yet turn out to be false.  So truth is not necessarily an adequate test of a rational belief.  In other words, a rational belief is not necessarily true, and an irrational belief is not necessarily false.  On the other hand, a rational belief needs to be reasonable or credible in the circumstances; that is, a rational belief is one that is justified by reason.

Although an irrational belief is not necessarily false, we can say that because an irrational belief is unreliable and more likely to be false than a rational belief, we should therefore be more skeptical about beliefs that are known to be or appear to be irrational than about rational beliefs.

It is believed by some philosophers (notably A.C. Grayling) that a rational belief must be independent of emotions, personal feelings or any kind of instincts.  Any process of evaluation or analysis, that may be called rational, is expected to be objective, logical and ‘mechanical’.  If these minimum requirements are not satisfied i.e. if a person has been influenced by personal emotions, feelings, instincts or culturally specific, moral codes and norms, then the analysis may be termed irrational, due to the injection of subjective bias.

So let us now look at some other possible objective tests of irrational belief, including logical fallacies, emotional or faith-based rather than evidence-based beliefs, beliefs based on insufficient supporting evidence, beliefs derived from confirmation bias, beliefs incompatible with science and internally incoherent beliefs, and any others we would like to discuss at this meetup.

Logical fallacies

A logical fallacy is faulty reasoning in argumentation resulting in a misconception.  A fallacious argument can be deductively invalid or one that has insufficient inductive strength.  For example, the argument that smoking does not cause cancer based on the anecdotal evidence of only one healthy smoker.

By accident or design, fallacies may exploit emotional triggers in the listener or interlocutor (e.g. appeal to emotion), or take advantage of social relationships between people (e.g. argument from authority).  By definition, a belief arising from a logical fallacy is contrary to reason and is therefore irrational.

Emotional, instinctive or faith-based rather than evidence-based beliefs

In western literature, reason is often opposed to emotions or instincts — desires, fears, hates, drives, or passions.  Even in everyday speech, westerners tend to say for example that their passions made them behave contrary to reason, or that their reason kept the passions under control, often expressed in colloquial terms as the dilemma between following ‘the head’ (reason) ‘or the heart’ (emotions).

Faith involves a stance toward some claim that is not, at least presently, demonstrable by reason.  Thus faith is a kind of attitude of trust or assent. As such, it is ordinarily understood to involve an act of will or a commitment on the part of the believer.  People do not usually have faith in something they do not want to believe in.  Religious faith involves a belief that makes some kind of either an implicit or explicit reference to a transcendent source.  The basis for a person’s faith usually is understood to come from the authority of revelation.[9]  Faith-based belief without evidence is considered to be a virtue by the religiously devout; but a ‘sin’ by rationalists.

Emotional, instinctive and faith-based beliefs are held on grounds other than evidence or reason, and according to the definitions given in the first part of this paper are irrational.  This is not to say that such beliefs are necessarily wrong, bad or undesirable – simply that they are not derived from reason.

Though theologies and typically do not claim to be irrational, there is often a perceived conflict or tension between faith and tradition on the one hand, and reason on the other, as potentially competing sources of wisdom and truth.  Defenders of traditions and faiths typically maintain that there is no real conflict with reason, because reason itself is not enough to explain such things as the origins of the universe, or right and wrong, and so reason can and should be complemented by other sources of knowledge.  The counter claim to this is that there are actual conflicts between faith and reason (for instances, the Trial of Galileo, creationism vs evolution, stem-cell research etc).

Some relatively recent philosophers, most notably the logical positivists, have denied that there is a domain of thought or human existence rightly governed by faith, asserting instead that all meaningful statements and ideas are accessible to thorough rational examination.[10]

Insufficient supporting evidence

Some beliefs are not necessarily based on emotion or faith, and are not entirely devoid of evidence, but there is insufficient evidence to justify the belief.  Beliefs in UFOs, alien abductions and conspiracy theories such as the so-called Moon Landings Hoax fall into this category.

Confirmation bias – cherry-picking the evidence

Confirmation bias is a tendency for people to favour information that confirms their preconceptions or hypotheses regardless of whether the information is true.  As a result, people gather evidence and recall information from memory selectively, and interpret it in a biased way.  The biases appear in particular for emotionally significant issues, for established beliefs and for conspiracy theories.

For example, there is some evidence that in a very small number of cases there are adverse reactions to some vaccines in some patients.  But this argument against vaccination overlooks the overwhelming benefits of vaccination in preventing and in some cases eradicating infectious diseases.  In other words, the anti-vaccination campaigners do not take into account evidence contrary to their fixed beliefs.  Thus the beliefs of anti-vaccination campaigners and some conspiracy theorists are based on faulty reasoning; and are therefore irrational.

 Incompatibility with science

It has long been held that rationality requires rigorous rules for deciding whether a proposition should be believed.  Formal logic and mathematics provide the clearest examples of such rules.  Science has also been considered a model of rationality because it proceeds in accordance with scientific methods which provide the rules for gathering evidence and evaluating hypotheses on the basis of this evidence.[11]

One of the main purposes of scientific methods is to eliminate subjective biases and interfering factors in order to test hypotheses.  This is why scientists use techniques such as controls and double blind tests that we often hear about in sceptical discussions.

Where a belief is incompatible with science, either the belief must be false or the science must be wrong – they can’t both be right.  For example, homeopathy is incompatible with the science of chemistry; water-divining is incompatible with the science of physics and astrology is incompatible with the science of astronomy.  On this ground alone, pseudo-sciences like these are irrational.

Internally incoherent beliefs

Coherentism is a theory of epistemic justification.  It implies that for a belief to be justified it must belong to a coherent system of beliefs. For a system of beliefs to be coherent, the beliefs that make up that system must “cohere” with one another.  In other words, some of a person’s justified beliefs are justified because they derive their justification from other beliefs.  For example, take my belief that tomorrow is Wednesday.  That belief can be justified by two other beliefs: my belief that today is Tuesday and my belief that Tuesday is immediately followed by Wednesday.  But, if my belief that tomorrow is Wednesday derives its justification from these other beliefs, then my belief that tomorrow is Wednesday is justified only if these other beliefs are justified.[12]  If today is Monday, then my belief that tomorrow is Wednesday is incoherent and unjustified.

For example, the claim of homeopathy that ‘like cures like’ is incoherent with the practice of diluting substances to the point where there is nothing but water in a homeopathic dose.  Homeopathy makes no sense, or in other words is internally incoherent and therefore irrational.  We can all probably think of other paranormal and pseudo-science beliefs that are internally incoherent and therefore irrational.

Summary

In summary, rationality is the state or quality of being rational, which means as being consistent with or based on or using reason.

Reason is thought by rationalists to be more reliable in determining what is true; in contrast to reliance on factors such as authority, tradition, instinct, intuition, emotion, mysticism, superstition faith or arbitrary choice.

The word rational can be used in several different contexts; but the context most relevant to skepticism is that of rational belief, because we use it as a filter to determine what we should be sceptical about.  We skeptics are not skeptical of everything.  We believe what it is rational to believe, and we are skeptical of irrational beliefs.

Two criteria have been proposed by Nozick for a rational belief:

  1. support by reasons that make the belief credible; and
  2. generation by a process that reliably produces true beliefs.

A rational belief is not necessarily true, and an irrational belief is not necessarily false.  On the other hand, a rational belief needs to be reasonable or credible in the circumstances; that is, a rational belief is one that is justified by reason.  It needs to pass objective tests of irrationality.

Objective tests of irrational belief include logical fallacies, emotional or faith-based rather than evidence-based beliefs, beliefs based on insufficient supporting evidence, beliefs derived from confirmation bias, beliefs incompatible with science, internally incoherent beliefs and possibly other tests.

Although an irrational belief is not necessarily false, we can say that because an irrational belief is unreliable and more likely to be false than a rational belief, we should therefore be more skeptical about beliefs that are known to be or appear to be irrational than about rational beliefs.

References:

Fieser, J. and Dowden, B. eds (2011) Internet Encyclopedia of Philosophy <http://www.iep.utm.edu/>

Honderich, T. ed (2005) The Oxford Companion to Philosophy, 2nd edition. Oxford University Press, Oxford.

Nozick, R. (1993) The Nature of Rationality, Princeton University Press, Princeton.


[1] Meaning reason in the philosophical sense as defined here, rather than in the colloquial sense of a reason meaning any explanation for an action or event, whether or not the explanation is based on reason in the philosophical sense.

[2] Deductive vs inductive reasoning is a possible topic for a future meetup?

[3] Nozick, 1993 p.xi

[4] The term ‘non-rational’ means neither rational nor irrational, and applies to matters unrelated to truth or falsity such as taste or aesthetics.

[5] Nozick, 1993 p.xiv

[6] For the purpose of this thought experiment, we assume that it does not rain every day and there is no predictable pattern of rainfall in the area in question.

[7] Most chemicals can be toxic in sufficiently large concentrations.

[9] Feiser and Dowden et al, 2011.

[10] Feiser and Dowden et al, 2011.

[11] Honderich et al, 2005 p. 786.

[12] Feiser and Dowden et al, 2011.

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Argument from Popularity

by Tim Harding

The informal fallacy known as argumentum ad populum means ’argument from popularity’ or ‘appeal to the people’.  This fallacy is essentially the same as ad numerum, appeal to the gallery, appeal to the masses, common practice, past practice, traditional knowledge, peer pressure, conventional wisdom, the bandwagon fallacy; and lastly truth by consensus, of which I shall say more later.

The Argument from Popularity fallacy may be defined as when an advocate asserts that because the great majority of people in general agree with his or her position on an issue, he or she must be right.[1]  In other words, if you suggest too strongly that someone’s claim or argument is correct simply because it’s what most people believe, then you’ve committed the fallacy of appeal to the people.  Similarly, if you suggest too strongly that someone’s claim or argument is mistaken simply because it’s not what most people believe, then you’ve also committed the fallacy.

Agreement with popular opinion is not necessarily a reliable sign of truth, and deviation from popular opinion is not necessarily a reliable sign of error, but if you assume it is and do so with enthusiasm, then you’re guilty of committing this fallacy.  The ‘too strongly’ mentioned above is important in the description of the fallacy because what most everyone believes is, for that reason, often likely to be true, all things considered.  However, the fallacy occurs when this degree of support is used as justification for the truth of the belief.[2]

It often happens that a true proposition is believed to be true by most people, but this is not the reason it is true.  In other words, correlation does not imply causation, and this confusion is the source of the fallacy, in my view.  For example, nearly every sane person believes that the proposition 1+1=2 is true, but that is not why it is true.  We can try doing empirical experiments by counting objects, and although this exercise is highly convincing, it is still only inductive reasoning rather than proof.  Put simply, the proposition 1+1=2 is true because it has been mathematically proven to be true.  But my purpose here is not to convince you that 1+1=2.  My real point is that the proportion of people who believe that 1+1=2 is true is irrelevant to the truth or falsity of this proposition.

Let us now consider a belief where its truth is less obvious.  Before the work of Copernicus and Galileo in the 15th and 16th centuries, most people (including the Roman Catholic Church) believed that the Sun revolved around the Earth, rather than vice versa as we now know through science.  So the popular belief in that case was false.

This fallacy is also common in marketing e.g. “Brand X vacuum cleaners are the country’s most popular brand; so buy Brand X vacuum cleaners”.  How often have we heard a salesperson try to argue that because a certain product is very popular this year, we should buy it?  Not because it is a good quality product representing value for money, but simply because it is popular?  Weren’t those ‘power balance wrist bands’ also popular before they were exposed as a sham by the ACCC?[3]

For another example, a politician might say ‘Nine out of ten of my constituents oppose the bill, therefore it is bad legislation.’  Now, this might be a political reason for voting against the bill, but it is not a valid argument that the bill is bad legislation.  To validly argue that bill is bad legislation, the politician should adduce rational arguments against the bill on its merits or lack thereof, rather than merely claim that the bill is politically unpopular.

In philosophy, truth by consensus is the process of taking statements to be true simply because people generally agree upon them.  Philosopher Nigel Warburton argues that the truth by consensus process is not a reliable way of discovering truth.  That there is general agreement upon something does not make it actually true.  There are several reasons for this.

One reason Warburton discusses is that people are prone to wishful thinking.  People can believe an assertion and espouse it as truth in the face of overwhelming evidence and facts to the contrary, simply because they wish that things were so.  Another is that people are gullible, and easily misled.

Another unreliable method of determining truth is by determining the majority opinion of a popular vote.  This is unreliable because on many questions the majority of people are ill-informed.  Warburton gives astrology as an example of this.  He states that while it may be the case that the majority of the people of the world believe that people’s destinies are wholly determined by astrological mechanisms, given that most of that majority have only sketchy and superficial knowledge of the stars in the first place, their views cannot be held to be a significant factor in determining the truth of astrology.  The fact that something ‘is generally agreed or that ‘most people believe’ something should be viewed critically, asking the question why that factor is considered to matter at all in an argument over truth.  He states that the simple fact that a majority believes something to be true is unsatisfactory justification for believing it to be true.[4]

In contrast, rational arguments that the claims of astrology are false include firstly, because they are incompatible with science; secondly, because there is no credible causal mechanism by which they could possibly be true; thirdly, because there is no empirical evidence that they are true despite objective testing; and fourthly, because the star signs used by astrologers are all out of kilter with the times of the year and have been so for the last two or three thousand years.

Another example is the claims of so-called ‘alternative medicines’ where judging by their high sales figures relative to prescription medicines, it is quite possible that a majority of the population believe these claims to be true.  Without going into details here, we skeptics have good reasons for believing that many of these claims are false.

Warburton makes a distinction between the fallacy of truth by consensus and the process of democracy in decision making.  Descriptive statements of the way things are, are either true or false – and verifiable true statements are called facts.  Normative statements deal with the way things ought to be, and are neither true nor false.  In a political context, statements of the way things ought to be are known as policies.  Political policies may be described as good or bad, but not true or false.  Democracy is preferable to other political processes not because it results in truth, but because it provides for majority rule, equal participation by multiple special-interest groups, and the avoidance of tyranny.

In summary, the Argument from Popularity fallacy confuses correlation with causality; and thus popularity with truth.  Just because most people believe that a statement is true, it does not logically follow that the statement is in fact true.  With the exception of the demonstrably false claims of astrology and so-called ‘alternative medicines’, popular statements are often more likely to be true than false (‘great minds think alike’); but they are not necessarily true and can sometimes be false.  They are certainly not true merely because they are popular.  This fallacy is purely concerned with the logical validity of arguments and the justification for the truth of propositions.  The identification of this fallacy is not an argument against democracy or whether popular political policies should or should not be pursued.

References:

Clark J. and Clark T., (2005) Humbug! The skeptic’s field guide to spotting fallacies in thinking Nifty Books, Capalaba.


[1] Clark and Clark, 2005.

[2] Feiser and Dowden et al, 2011.

[4] Warburton, 2000.

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Two twin fallacies

by Tim Harding

Seasoned skeptics may be familiar with two well-known logical fallacies:

  1. The ‘Argument from Personal Abuse’ or the ad hominem argument (playing the man instead of the ball); and
  2. The deductive form of the ‘Argument from Authority‘ or ‘Appeal to Authority’. (The inductive form is not necessarily a fallacy).

When you think about it, these fallacies make the same error of logic – they both draw conclusions from the character or motives of the arguer rather than the premises and form of the argument.

In informal logic, these are known as fallacies of defective induction, where it is argued that a statement is true or false because the statement is made by a person or source that is commonly regarded as authoritative or not authoritative.  The most general structure of this argument is:

   Premise 1: Source A says that statement p is true.
   Premise 2: Source A is authoritative.
   Conclusion: Therefore, statement p is true.

Conversely:

  Premise 1: Source B says that statement p is true.
  Premise 2: Source B is a ‘bloody idiot’.
  Conclusion: Therefore, statement p is false.

We skeptics are often skeptical of conspiracy theories, such as the so-called Moon Landings Hoax.  Conspiracy theories like these are often a special case of the ad hominem argument, for example:

   Premise 1: NASA claims to have landed men on the Moon;
   Premise 2: Governments can’t be trusted;
   Premise 3: NASA is a government agency;
   Conclusion: Therefore, NASA’s claim is false.

These arguments are fallacious because the truth or falsity of the claim is not necessarily related to the attributes or motives of the claimant, and because the premises can be true, and the conclusion false (an authoritative claim can turn out to be false).  If the premises can be true, but the conclusion can be false, then the argument is logically invalid. (A logically valid argument is one where if the premises are true, then the conclusion must be true by virtue of the argument’s logical structure).

An exception can be made for an ad hominem argument if the attack goes to the credibility of the arguer. For instance, the argument may depend on its presenter’s claim that he’s an expert. (That is, the ad hominem argument is undermining a legitimate Argument From Authority). Trial judges allow this category of refutation in appropriate cases.

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Begging the question

by Tim Harding

Setting aside for a moment whatever personal views we might have about the morality of abortion, consider the following argument:

   Premise 1: Murder is morally wrong;

   Conclusion: Therefore, abortion is morally wrong.

Is this argument logically valid?  Probably not, but let’s analyse the form of the argument to make sure:

    Premise 1: A is B;

    Conclusion: Therefore, C is B.

An argument of this form is logically invalid, i.e. the conclusion can be false even when the premises are true.  Or in other words, the conclusion does not necessarily follow from the premises.

OK, how about this argument:

   Premise 1: Abortion is murder;

   Premise 2: Murder is morally wrong;

   Conclusion: Therefore, abortion is morally wrong.

Is this argument valid?  The form of this argument is:

   Premise 1: A is B;

   Premise 2: B is C;

   Conclusion: Therefore, A is C.

In this second case, the conclusion necessarily follows from the premises. That is, if the premises are true (which they may or may not be), then the conclusion must be true by virtue of the logical structure of the argument. So this form of this argument is logically valid. However, if one or more of the premises is false, then the conclusion may also be false (even though the argument is valid). This example also illustrates the importance difference between validity and truth.

The first argument was missing a premise, which when included, turned the argument from an invalid one to a valid one.  This is an instance of the formal fallacy known as the Fallacy of the Unstated Major Premise or ‘Begging the Question’.

The Latin name for it is petitio principia, meaning a request for the beginning or premise’.  Or in other words, this fallacy is committed when one makes an argument assuming a premise that is not explicitly stated.  It is not to be confused with the meaning of ‘raising the question’, which is sometimes mistakenly referred to as ‘begging the question’ in the popular media.

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Rationality and truth

by Tim Harding

Rationality is the state or quality of being rational, which means being consistent with or based on or using reason.  Reason is thought by rationalists and skeptics to be more reliable in determining what is true; in contrast to reliance on factors such as authoritytradition, instinct, intuitionemotionmysticismsuperstitionfaith or arbitrary choice.

Harvard philosophy professor Robert Nozick has proposed two criteria for rational belief:

  1. support by reasons that make the belief credible (e.g. scientific evidence); and
  2. generation by a process that reliably produces true beliefs (e.g. the scientific method).[1]

For instance, until early December 2010, science told us that the element arsenic is toxic to all life on Earth, in even very small concentrations.  But then NASA announced that scientists had discovered a microorganism in California’s Mono Lake able to thrive and reproduce using arsenic instead of phosphorus in its biochemistry.[2] In terms of Nozick’s criteria, it was rational until December 2010 to believe that arsenic is toxic to all life on Earth, even though we now know that the belief was false.  Was it rational to hold this belief after the NASA announcement?  Using the same criteria, our answer would be ‘no’.

A statement is true when it represents how things are; true statements are ones that correctly describe reality; true statements correspond to the way the world really is. But as we have seen, a rational belief is not necessarily true.  Conversely, an irrational belief is not necessarily false.  For example, a prediction made by a psychic can turn out to be true by coincidence.  On the other hand, a rational belief needs to be reasonable or credible in the circumstances; that is, a rational belief is one that is justified by reason.

What we can say that is because an irrational belief is unreliable and more likely to be false than a rational belief, we should therefore be more skeptical about beliefs that are known to be or appear to be irrational than about rational beliefs.

References

[1] Nozick, R. (1993) The Nature of Rationality, Princeton University Press, Princeton.

[2] http://www.nasa.gov/topics/universe/features/astrobiology_toxic_chemical.html

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The David and Goliath Fallacy

by Tim Harding

The biblical parable of David and the Goliath is taught to many children throughout the Western world and the Middle East.  Goliath was a huge armoured and weapon-carrying champion, who was defeated by a small shepherd boy using only a slingshot and stone.  This parable is often cited to show how an underdog with ‘right on his side’ can defeat much a more powerful opponent.

Andrea_del_Castagno_002

In some cases, this parable is extended into a logical fallacy that attempts to paint large and powerful organisations as bad or wrong because they are large and powerful.  For example, anti-science advocates often disparagingly refer to ‘Big Pharma’, implying that the pharmaceutical industry is bad, at least in part, because it is big.  Never mind that, in terms of retail sales dollars, the placebo industry (or so-called ‘alternative medicine’) is of a similar order of magnitude these days.  Similar disparagements are made against medical science, the medical profession and even government agencies on the grounds of their size and influence.

The David and Goliath Fallacy takes roughly the following form:

   Premise 1: There is a conflict between two organisations A and B.

   Premise 2: A is much larger and more powerful than B.

   Conclusion: Therefore, A is bad or wrong, compared to B which is good or right.

Like all logical fallacies, this argument is invalid because the conclusion does not necessarily follow from the premises.  Small organisations can be bad and/or wrong; and large organisations can be good and/or right. In some ways, the David and Goliath Fallacy can be viewed as a perverse over-correction of the aphorism ‘Might Makes Right’.

One of the consequences of this fallacy is that claiming underdog status against a more powerful ‘Goliath’ can give moral licence to poor behaviour during conflicts, to create a ‘more even contest’.  For example, small organisations like the so-called Australian Vaccination-skeptics Network frequently make false or unsubstantiated claims, with the lame excuse that they do not have the resources to back up their claims with evidence. The David and Goliath Fallacy has been used during ideological debates in attempts to justify intellectual property theft and even terrorism.

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