Welcome to "Evaluating Reasoning"

In the previous chapter, you learned how to analyse an argument by breaking it down into its "skeleton" (conclusions, reasons, and assumptions). Now, it is time for the next step: evaluating it. Evaluating means judging the quality and strength of the reasoning. Think of yourself as a structural engineer checking a building for cracks. You aren't just looking at what the building is made of; you are checking if it is strong enough to stand up!

This skill is vital for Paper 4, Question 2, where you will usually be asked to evaluate the strength of the reasoning in one of the provided documents.

1. The "Closed List" of Informal Fallacies

A fallacy is a flaw in the logic of an argument. The syllabus provides a specific "closed list" of fallacies you should look for. Don't worry if the names sound fancy; the concepts are things you see in everyday life!

Logical Flaws to Spot:

  • Conflation: Treating two different things as if they are the same.
    Example: Treating "freedom of speech" as exactly the same thing as "the right to say anything, anywhere, without any consequences."
  • Equivocation: Using the same word or phrase in two different senses within the same argument.
  • Circular Reasoning: This is when the conclusion is just a restatement of one of the reasons. You are essentially saying "A is true because A is true." (This includes "begging the question").
  • Causal Fallacy: Claiming that because one thing happened after another, the first thing caused the second. This includes post hoc (after this) and cum hoc (with this).
  • Generalisations:
    • Rash generalisation: Drawing a wide conclusion from a tiny or unrepresentative sample.
    • Sweeping generalisation: Applying a general rule to a specific case that is an exception.
  • Straw Man: Misrepresenting an opponent’s argument to make it look weaker and easier to defeat.
  • Restriction of Options (False Dichotomy): Presenting only two choices (e.g., "Either we do X or the world ends") when other possibilities actually exist.
  • Slippery Slope: Arguing without proof that one small step will inevitably lead to a major, usually disastrous, outcome.
  • Personal Attack (Ad Hominem): Attacking the person making the argument rather than the argument itself.
  • Counter Attack (Tu Quoque): Rejecting a criticism because the person making it is also "guilty" of it. (e.g., "You can't tell me to stop smoking; you smoke too!").

Special Differences for Your Exam Year:

If you are taking exams in 2027, you also need to look for Invalid Deduction (affirming the consequent or denying the antecedent). If you are taking exams in 2028 and beyond, the list includes Argument from Ignorance (claiming something is true simply because it hasn't been proven false).

Quick Review: A fallacy isn't just "being wrong." It is a specific break in the logical link between a reason and a conclusion.

2. Assessing Weaknesses in Reasoning

Sometimes an argument doesn't have a "named" fallacy, but it is still weak. In Paper 4, you should look for these four specific areas of weakness:

1. Support: Look at the reasons. Even if they are true, do they actually lead you to the conclusion? If a reason is "thin" or only covers a tiny part of the conclusion, the support is weak.

2. Consistency: Does the author contradict themselves? If Reason A says "We must save money" and Reason B says "We should spend millions on a new park," there is an inconsistency that weakens the whole document.

3. Reliance: Does the argument rely too heavily on unstated assumptions or a single, questionable piece of evidence? If that one "pillar" falls, the whole argument collapses.

4. Counter-positions: A strong argument acknowledges the other side. A weak one ignores counter-assertions or fails to respond to counter-arguments effectively. (Note: For 2028 exams, responding to significant counter-positions is a major focus for Question 4 as well!)

3. Rhetorical Devices: Appeals and Analogies

Authors often use "shortcuts" to persuade you. You need to identify these and decide if they actually help the argument or just mask a lack of logic.

Appeals

An appeal is an attempt to persuade by tapping into something other than pure logic. Common ones include:

  • Appeal to Authority: "This must be true because a famous doctor said so" (even if the doctor isn't an expert in this specific field).
  • Appeal to Popularity: "Everyone is doing it, so it must be right."
  • Appeal to Tradition: "We have always done it this way, so we shouldn't change."
  • Appeal to Emotion: Using pity, fear, or anger to cloud the reader's judgment.

Analogies

An analogy compares the current situation to a similar one to make a point. To evaluate an analogy, ask: "Are these two things actually similar in the ways that matter?" If they are different in a fundamental way, the analogy is faulty.

4. How to Write Your Evaluation (Step-by-Step)

In the exam, simply naming a fallacy is not enough for full marks. You must explain how it affects the argument. Don't worry if this seems tricky at first; follow these steps:

Step 1: Identify. Name the flaw or weakness (e.g., "There is a conflation here...").

Step 2: Locate. Quote or paraphrase the specific part of the document where it happens.

Step 3: Explain. Explain why it is a flaw in this specific context (e.g., "...because the author treats 'popularity' as if it were the same as 'quality', which are actually two different things.").

Step 4: Assess Impact. State how much this weakens the Main Conclusion. If the flaw is in a minor reason, the argument might still be okay. If the flaw is in the core logic, the conclusion is unsupported.

Key Takeaway: Evaluation is about finding the gap between what the author says and what they have actually proven.

5. Common Mistakes to Avoid

  • Don't just disagree: The syllabus is very clear—your own opinion on the topic is not a weakness in the reasoning. Evaluate the logic provided, not whether you like the topic.
  • Don't confuse "Explanation" with "Argument": You are looking for flaws in persuasion. If the author is just explaining why something happened (a narrative), it isn't an argument to be evaluated.
  • Don't use "Latin" unnecessarily: You don't have to use terms like ad hominem or tu quoque, though you can if you use them correctly. Plain English (e.g., "Personal attack") is perfectly fine!

Cross-reference: For more on how to use these evaluations to build your own case, see the chapter "Construct a substantial reasoned argument from multiple documents."