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How not to construct arguments

This page is taken from the University of Plymouth critical thinking guide (2008), adapted from Warburton, N. (1998) Thinking, from A to Z. London: Routledge

The following examples are a humorous guide to help you to spot faulty logic. Look out for these common errors when analysing academic texts and try to avoid these faults in your own arguments.


Ignore alternative explanations

  • I become bad tempered if I have a hangover.
  • I am bad tempered.
  • Therefore I must have a hangover.


  • Thanks for offering to help me hammering in this fence post.
  • When I nod my head, you hit it.

Generalise from anecdotal evidence

  • My friend tried acupuncture and it worked.
  • Therefore acupuncture can cure anything.

Make assumptions

  • The meal contains nuts, so the patients should not eat it.

Think in black and white

  • The patient is either completely mad, or completely sane.


  • Some people prefer an early start, but everyone likes a lie in.

Use the wrong dictionary definitions

Using dictionary definitions that are:
  • Short
  • Vague
  • Superficial
  • Unrelated to the context.

Assume correlations are causes

  • There is a strong link between people's shoe size and the size of their vocabulary.
  • Therefore having a large vocabulary causes your feet to grow.


  • Let's consider whether music should be taught in schools.
  • My great-grandmother used to send me to sleep by playing lullabies on the trombone.

Not telling the whole story

  • Only three severe adverse reactions have been recorded [This week].


Emotive language

  • This kind of stupidity is the main threat to the health of our precious young people.

Faulty reasoning

  • Witches keep black cats.
  • The lecturer keeps a black cat.
  • Therefore the lecturer is a witch.

Use jargon

  • The French modus vivendi is too laissez faire (The French way of life is too relaxed / laid back).

Accepting ideas uncritically

Accepting an argument without criticism because the person who said it has high status:

• Nietzsche, who was really famous and wonderful and knew everything, said to take a whip when approaching a woman, so it's OK to hit your wife.

Statements that don't follow on

  • Many cats have tails.
  • Some cats like milk.
  • So the corner shop will be closed on Sundays.

'Persuader' words

Using words that try to persuade the reader of a particular viewpoint.

Obviously we should follow every instruction issued by a doctor.


  • From the two case studies, it is clear that this outcome is inevitable for measles patients.

Generalise research findings inaccurately

Writing 'research has shown that' followed by absolute statements:
  • Nuts are poisonous to people.
  • The earth is flat.
  • Bumble bees cannot fly.

Wishful thinking

  • Clearly, sending all patients home at this stage will reduce the cost of care without significantly impairing their recovery.

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