Claims and Evidence

A claim needs to be supported by evidence to be believable.

e.g. Singapore is a hot country (claim), the average daytime temperature is around 30 degrees (second claim), according to the Singapore Meteorological Department (evidence – published data). Alternatively, you can try standing outside for several days throughout the year (evidence – personal experience) or ask a friend who is a local (evidence – eyewitness testimony).

Types of Evidence

  1. Personal experience (direct observation)
  2. Eyewitness testimony
  3. Published or self-collected data
  4. Current or historical examples/anectdotes
  5. Logical inference or deduction
  6. Expert authority

Note this is just one classification scheme!

Common Thinking Errors (Fallacies)

Argument from ignorance

  • The fact that we have no proof that A isn’t true is taken as a reason to believe it’s true
    • ‘The earth must be flat because it appears to be and no-one has proven otherwise’

Inferential fallacy

  • A is mistakenly accepted as a reason to accept claim B
    • ‘Prof Smith is a famous economist so his recommendation to buy these stocks and shares must be good’

Mass appeal

  • Many people believe A, so A is taken as true
    • ‘Six million customers can’t be wrong!’ (They can, when the product is later recalled!)

Confusing correlation with causation*

  • A and B frequently happen together, so A is taken to cause B
    • ‘African Americans are genetically better at basketball – almost all NBA players are black’

Biased sample*

  • A is taken to be true because it is true in sample B, when sample B doesn’t reflect the underlying population
    • ‘Singaporean university students in the UK get very good grades. Singaporean students are better than UK students’

Misleading average*

  • Average A is used as the basis of reasoning, when it is the inappropriate type of average (mean, medium, mode)
    • ‘Life expectancy for males in Singapore is 79 so I can expect to live until that age’

*Common quantitative reasoning errors

Types of Challenge

No evidence – there is no evidence behind the claim (perhaps it relies on other claims, which need evidence), it is actually an opinion

Insufficient evidence – the claim provides supporting evidence, but on closer examination the evidence doesn’t actually support the claim

Weak evidence – the claim provides supporting evidence, but the evidence is rather weak due to the weaknesses of the type of evidence used (e.g. a single example is given as evidence)

Distinguishing – the claim lumps together (conflates) two things which have a key difference

Thinking error or fallacy – one of the common critical thinking errors elaborated above