Critical Thinking 6: Fallacies and Cognitive Biases

There are a great many different fallacies and a great many different cognitive biases: probably enough to keep me going for years if I was to discuss one each week on this blog series. What I want to do here, though, is just to consider the question of what fallacies and cognitive biases actually are, and how they relate to each other. This is a contentious enough subject in itself.

A fallacy is normally described as a flaw in reasoning, or a type of mistake whereby people draw incorrect conclusions from the reasons they start with. This would be correct when applied to formal fallacies, but I think incorrect when applied to the more interesting and practically relevant informal fallacies. Here’s a simple example of a formal fallacy (one known as affirming the consequent):

Good Catholics attend mass regularly.

Bridget attends mass regularly.

Therefore Bridget is a good Catholic.

You might think this was quite a reasonable conclusion to draw from the reasons given. However, it is not a necessary conclusion. You don’t have to be a good Catholic to attend mass regularly, and it’s quite possible that Bridget is an uncertain enquirer, or a bad Catholic trying to keep up appearances, or a Religious Studies scholar doing field research into Catholicism. A conclusion that is not necessarily true is not valid, and thus a formal fallacy.

However, it may be reassuring to reflect that the vast majority of arguments we actually use in practice are formal fallacies. Many of them are inductive (see Critical Thinking 2), and even those that are not inductive may be deduction (like the example above) of a kind that is formally invalid but actually reasonably enough most of the time. Formal fallacies are thus of little interest from the practical point of view. Informal fallacies, on the other hand, tell us much more about unhelpful thinking, even though they may actually be formally valid in some instances.

Informal fallacies are just unjustified assumptions: for example, the assumption that some objectionable personal attribute in the arguer refutes their argument (ad hominem); or that there are only two choices in a situation where there is actually a spectrum of options (false dichotomy); or the assumption that using your conclusion as a reason provides an informative argument (begging the question). What is objectionable about arguments involving these moves often depends on the circumstances, and it requires thoughtful judgement rather than just applying black-and-white rules. But that’s also the indication that these fallacies actually matter in everyday life.

Informal fallacies are unjustified assumptions identified by philosophers. The only genuine difference between informal fallacies and cognitive biases, as far as I can see, is that cognitive biases are unjustified assumptions identified by psychologists and often tested through experiment. Psychologists may explain our tendency to make these particular kinds of unhelpful assumptions in terms of the physical, social and evolutionary conditions we emerge from, but in the end these kinds of explanations are less central than the identification of the bias itself. Usually cognitive biases can be ‘translated’ into fallacies and vice-versa. For example, the in-group bias (tendency to favour the judgements of your own group) is equivalent to the irrelevant appeal to the authority of the group (or its leaders), irrelevant appeal to popularity within the group, or irrelevant appeal to tradition in the group, all of which are recognised informal fallacies. The outcome bias, whereby we judge a past decision by its outcome rather than its quality at the time, involves an irrelevant appeal to consequences.

Philosophers and psychologists thus both have very useful things to tell us about what sorts of mistakes we are likely to make in our thinking, and insofar as their different contributions are practically useful, they tend to converge. I would also argue that this convergence of useful theory relates closely to the avoidance of metaphysics (see cognitive biases page). Despite the widespread idea that fallacies are faults in reasoning, they really have nothing to do with reasoning in the strict sense of logical validity. They are all about the unhelpful assumptions we often tend to make.


See if you can identify  and describe the type of unhelpful assumptions being made in these video clips. You don’t necessarily need to know the formal titles of the fallacies involved to identify why they are a problem.




About Robert M Ellis

Robert M Ellis is the founder and chair of the Middle Way Society, and author of a number of books on Middle Way Philosophy, including the introductory 'Migglism' and the more in-depth 'Middle Way Philosophy' series. He has a Christian background, and about 20 years' past experience of practising Buddhism, but it was his Ph.D. studies in Philosophy that set him on the track of developing a systematic account of the Middle Way beyond any specific tradition. He has earned his living mainly by teaching, and more recently by online tutoring.

4 thoughts on “Critical Thinking 6: Fallacies and Cognitive Biases

  1. 1.
    Opposition speaker ‘rich are 10% richer, poor 10% poorer ‘ Perhaps valid or unjustified, a dichotomy – informal fallacy.
    Tory PM ‘All income levels are better off’- begging the question.
    Tory counter argument to first statement ‘Do Lib Dems (then in opposition) want the poor to be poorer and the rich less wealthy?’ –
    informal fallacy, a personal attack – ad hominem.

    Bush ‘with us or against us’ unjustified assumption, unhelpful thinking, therefore an informal fallacy.

    Scientist ‘Ecstacy is less harmful than horse riding’ it may be a valid assumption, two choices, drugs or horse riding, a false dichotomy – an informal fallacy.
    ‘Support for scientist, no support for Home Secretary’ this affirms the consequence – a formal fallacy.

    4. Muppets ‘ vertical videos are bad horizontal ones are good’, -two choices, an informal fallacy.
    ‘Vertical videos make a thin, incomplete picture’ affirming the statement. A formal fallacy.

  2. In the first dialogue the LibDem MP Simon Hughes argues that despite the improvement of the economy, the poor have become worse off under the Thatcher government. Margaret Thatcher counters that all levels of income are better off than when she came to power. This is indeed highly likely over an 11 period but doesn’t take into account an equally likely rise in the cost of living which combined with salary increases determines the standard of living. Therefore she’s missing out or ignoring contributing factors here which could be construed as confirmation bias. She then also argues that Hughes would rather the poorer be poorer provided that the rich were less rich suggesting that his economic model is a very dogmatic one – ie you can only have one or the other. This is arguably a false dichotomy as there are many examples of economies that have been able to generate significant wealth while at the same time having a lot more equal distribution of it.

    2. George Bush’s famous quote “You are either with us, or you are with the terrorists” is a clearer example of a false dichotomy.

    3. In this example, the interviewer uses to an extent the ad hominim fallacy by accusing David Knutt of being crass, (showing no intelligence or sensitivity) and glib (insincere and shallow) in his comparison of the dangers of horse riding with the taking of ecstasy rather than considering (or even reading) the merits(or not) of his argument. David Knutt makes a couple of appeals to popularity at the end of the video by talking about the letters of support he has had and the question time audience siding with his argument rather than the home secretary’s.

    4. I don’t see any problem with the last argument (and presume it was a trick question). In fact, vertical video syndrome has been a concern of mine for a number of years now and I feel it needs to be stamped out ruthlessly before its danger spreads (for many of the reasons stated so articulately in the video) . I am therefore glad you have brought this important issue to the attention of a wider audience.

  3. I did not do a further Critical Thinking blog this week as I was away. However, they will continue next week. Here are my answers on the exercise here.

    1. Margaret Thatcher uses a straw man fallacy (misrepresenting someone else’s position in a way that makes it easier to attack) because she misrepresents Socialism by putting it in terms that no socialist would accept.

    2. Bush offers a false dichotomy. Being with the terrorists or against them is not the only two possible options. E.g. one could deplore both his and the terrorists’ policies.

    3. David Knutt offers an interesting analogy between ecstasy and horse-riding. He makes a good point with the analogy, but it does have some weaknesses that he is rather reluctant to acknowledge. The main problem is that statistics about fatalities and serious injuries are not the only indicator of danger – in the case of ecstasy there could be danger of addiction or of longer-term mental or physical health effects, neither of which are the case with horse-riding.

    4. I take it you’re not serious here, Barry! This is a comic example of a slippery slope fallacy, in which worse and worse things are assumed to happen as a result of a disapproved-of action. But at every stage of the presumed slippery slope the increasingly bad effects may or may not happen. Compare common arguments against legalising hard drugs or legalising voluntary euthanasia which make similar assumptions.

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