Flaws & Fallacies
Identify and explain the most common errors in reasoning recognised by Cambridge A-Level Critical Thinking.
Key Terms
Common Fallacies in Cambridge Exams
Cambridge examinations frequently ask students to identify and explain flaws. The most commonly tested fallacies include: ad hominem, false dichotomy, slippery slope, hasty generalisation, circular reasoning, appeal to authority, straw man, post hoc (false cause), and appeal to popularity (bandwagon).
When identifying a flaw, always: (1) name the flaw, (2) quote the relevant part of the text, and (3) explain why it is a flaw — why does it weaken the argument?
"We should not listen to Dr Smith's views on climate change because he drives a large car."
Analysis: This attacks Dr Smith's personal behaviour rather than engaging with his arguments. Even if he does drive a large car, this does not address whether his climate arguments are valid.
"Either we implement this policy immediately, or we accept the collapse of public services."
Analysis: This presents only two options (implement now OR collapse), ignoring other possibilities such as phased implementation, alternative policies, or reform.
"If we allow students to use calculators, they will stop practising mental arithmetic. Eventually, basic numeracy will disappear from our society."
Analysis: Each step in the chain is assumed without justification. Students using calculators does not necessarily lead to inability to think numerically, and there is no evidence for the eventual outcome claimed.
"All the teenagers I know are addicted to their phones. Young people today are clearly incapable of self-control."
Analysis: A conclusion about all young people is drawn from a small, likely non-representative personal sample. The word "all" in the conclusion cannot be supported by such limited evidence.
Less Common but Important Fallacies
Post Hoc Ergo Propter Hoc (false cause): Assuming that because B followed A, A caused B. "After the new manager arrived, sales dropped — she must be incompetent." This confuses temporal sequence with causation.
Straw Man: Misrepresenting an opponent's argument in a weaker form to make it easier to attack. "Critics say we should consider reducing car use. These anti-progress activists want to return to the Stone Age."
Circular Reasoning (Begging the Question): "The Bible is true because it is the word of God, and God would not lie."
"I wore my lucky socks and passed the exam. My lucky socks must help me succeed."
Analysis: The exam was passed after wearing the socks, but the socks were not the cause. Many other factors (preparation, ability) explain the success.
Evaluating the Severity of Flaws
Not all flaws are equally damaging to an argument. A minor flaw in one piece of evidence does not necessarily destroy an argument supported by multiple strong reasons. When evaluating, consider: (1) how central is the flawed element to the argument? (2) Can the conclusion still stand without that element? (3) Is the flaw about form (logical structure) or content (truth of premises)?
Argument with one weak anecdote among three strong statistical pieces of evidence.
Analysis: Pointing out the anecdotal evidence as a flaw is valid, but the overall argument may still be reasonably strong given the other evidence. In a Cambridge evaluation question, acknowledge the flaw but also note the argument's remaining strength.
Cambridge Exam Tips
- 💡Always explain a flaw, not just name it. "This is an ad hominem" alone scores low marks. Explain WHY attacking the person doesn't undermine the argument.
- 💡Quote the specific sentence or phrase that contains the flaw to show Cambridge examiners exactly what you are referring to.
- 💡One argument can contain multiple flaws. Read carefully and identify all of them.
- 💡Distinguish between a flaw in reasoning (logical error) and a flaw in evidence (weak/irrelevant evidence) — both matter.