Thinking Skills (9694) | Evaluate reasoning

Welcome to Evaluate Reasoning!

Hello! This is one of the most exciting parts of Critical Thinking. You’ve already learned how to take apart an argument (Analyse Reasoning). Now, it’s time to become the judge!

In this chapter, you will develop the essential skill of identifying when and how an argument goes wrong. We look at two main types of error:
1. Flaws in Reasoning: Errors in the logical structure itself (e.g., using bad evidence).
2. Weaknesses in Reasoning: Failures in how the argument is supported or defended (e.g., failing to address an obvious counter-point).

Mastering this section is crucial because evaluating arguments is the core of Critical Thinking. Let's dive in!

Section 7.1: Identifying Flaws in Reasoning

A Flaw is a fundamental error in the logical structure of an argument. When you identify a flaw, you are showing that even if the reasons (premises) were true, the conclusion might still not follow.

1. Flaws involving Language and Definitions

Equivocation and Conflation

These two errors involve playing fast and loose with words.

• Equivocation: This happens when the reasoning tacitly shifts from one meaning of a word or expression to another halfway through the argument, concealing a step.
  Example: "Feathers are light. What is light cannot be dark. Therefore, feathers cannot be dark." (The word 'light' shifts from meaning 'low weight' to 'bright'.)


• Conflation: This means treating two different words or concepts as if they were interchangeable, even though their meanings are distinct.
  Example: Arguing that because 'A is popular' and 'A is famous' mean roughly the same thing, the argument uses the popularity of a TV show to prove its quality (confusing popularity with excellence).
  Impact: Both flaws destroy the logical link between the reasons and the conclusion, making the argument invalid.

2. Flaws involving Circularity

Circular Argument and Begging the Question

These flaws essentially assume what they are trying to prove.

• Circular Argument: Relying on the claim itself (or a rephrased version of the claim) in order to prove it.
  Example: "Ghosts exist because I saw a spirit. The fact that I saw a spirit proves ghosts exist."


• Begging the Question: Focusing an argument on an uncontroversial aspect while stipulating or assuming the key, controversial point. Often, this involves defining a term in a way that already guarantees the conclusion.
  Example: "Murder is morally wrong, so capital punishment (state-sanctioned killing) should be abolished." (This assumes capital punishment is equivalent to 'murder', which is the key point under debate.)
  Impact: These arguments provide no real support. If you reject the premise, you must reject the conclusion, because the premise is the conclusion.

3. Flaws involving Deductive Logic

Invalid Deduction

This refers to common formal fallacies like Affirming the Consequent or Denying the Antecedent.

Quick Analogies:
1. If A, then B. (If it rains (A), the ground is wet (B)).
2. Affirming the Consequent: "The ground is wet (B). Therefore, it must have rained (A)." (Invalid! A sprinkler might have caused B.)
3. Denying the Antecedent: "It did not rain (Not A). Therefore, the ground is not wet (Not B)." (Invalid! Again, a sprinkler might have caused B.)
Impact: The conclusion is not validly drawn from the premise, rendering the argument logically unsound.

4. Flaws involving Causality

Causal Flaw

This occurs when an arguer incorrectly assumes that correlation implies causation.

• Post hoc ergo propter hoc (Post hoc): Claiming that because one event follows another, the first event must have caused the second. (After this, therefore because of this.)
  Example: "I wore my lucky socks today, and then I passed the exam. The socks caused my success."


• Cum hoc ergo propter hoc (Cum hoc): Claiming that because two events occur together, one must cause the other, ignoring potential common causes or coincidence. (With this, therefore because of this.)
  Example: "Ice cream sales and crime rates both go up in the summer. Ice cream consumption must cause crime." (The common cause is heat/summer.)
  Impact: The claimed connection between cause and effect is based on insufficient evidence or correlation, significantly weakening the support for the conclusion.

5. Flaws involving Generalisations

• Rash Generalisation (Hasty Generalisation): Basing a generalisation on inadequate or insufficient evidence (a sample that is too small).
  Example: "I met two rude people from Country X. Therefore, everyone from Country X is rude."


• Sweeping Generalisation: Making a generalisation but failing to allow for reasonable exceptions.
  Example: "All drivers who speed are dangerous criminals who should be jailed." (Fails to allow for necessary exceptions, like an emergency.)
  Impact: The premise does not justify the broad scope of the conclusion, making the argument unreliable.

6. Flaws involving Conditions

• Restriction of Options (False Dichotomy / False Dilemma): Denying the possibility of moderate opinions or actions by claiming that anyone who rejects one extreme must accept its opposite (the "either/or" trap).
  Example: "You either love our new city centre policy or you hate the city entirely." (Ignores the possibility of moderate agreement or constructive criticism.)


• Confusion of Necessary and Sufficient Conditions: Misinterpreting what is required for an event to happen.
  Necessary Condition: A condition required (must be present) but not enough on its own. (e.g., Oxygen is necessary for fire.)
  Sufficient Condition: A condition that is enough on its own to guarantee the result, but not required. (e.g., Getting a 90% is sufficient to pass the exam, but 70% would also be enough.)
  The Flaw: Treating a necessary condition as sufficient, or vice versa.
  Analogy Aid: Think of a car. Having fuel is Necessary to drive. Turning the key is Sufficient to start the engine. The flaw is saying: "Since the car has fuel, it will start." (But it needs the key turned too – confusing necessary for sufficient.)
  Impact: These flaws create arbitrary limits or misrepresent the actual requirements for the conclusion to be true.

7. Flaws involving Distraction and Misrepresentation

• Slippery Slope Argument: Opposing a moderate proposal by claiming, without sufficient reason, that it will inevitably lead to a chain of disastrous, extreme consequences.
  Example: "If we allow students to use phones in the library, soon they will be watching movies and ignoring all work, and then the entire university system will collapse."


• Personal Attack (Ad hominem): Criticising the opponent personally (their character, background, or motives) instead of responding to the substance of their argument.
  Example: "We cannot trust the Mayor's plan for the new park; he’s a known liar and cheats on his taxes."


• Counter-attack (Tu quoque): Rejecting criticisms on the grounds that the opponent (or other people) is guilty of the same or equally objectionable conduct. (The "you too!" defence).
  Example: Person A says: "Smoking is bad for your health." Person B replies: "Well, you used to smoke five years ago, so your argument is invalid."


• Straw Man Argument: Misrepresenting the opponent's argument to make it seem weaker or more extreme than it actually is, so that it is easier to refute.
  Example: Opponent argues for "modest carbon taxes." The arguer claims: "My opponents want to destroy our economy and force everyone into poverty just to save a few trees!"
  Impact: These flaws introduce irrelevant information (personal characteristics, hypothetical disasters, misrepresentations) designed to distract the audience from the actual logical merit of the argument.

Section 7.2: Identifying Weaknesses in Reasoning

A Weakness is not a logical error like a flaw, but rather a failure to provide robust or proportionate justification, or a failure to defend the argument adequately. These issues make the argument less convincing or less robust.

1. Weak Support

This occurs if the reasoning only supports a moderate claim, but a much stronger conclusion is drawn.

• Support: It is a weakness if moderate evidence or an intermediate conclusion is used to support a final conclusion that would only logically follow from a much stronger version of the claim.
  Example: Evidence shows that "Most people prefer public transport." Conclusion drawn: "Public transport should immediately replace all private car ownership in the city." (The evidence supports increased investment, not the extreme conclusion.)
  Impact: The argument fails to justify the scope or intensity of its final conclusion.

2. Inconsistency

Arguments must be logically coherent.

• Consistency: It is a weakness if one part of the reasoning contradicts, or is inconsistent with, another part.
  Example: An author argues for maximum freedom of speech but then suggests that certain viewpoints (which he dislikes) must be censored.
  Impact: Contradictions undermine the author's credibility and make the entire line of reasoning unreliable.

3. Questionable Reliance

This is about the foundations of the argument.

• Reliance: It is a weakness if the argument relies on an unsupported claim, a questionable stipulative definition, or an unstated assumption which is controversial.
  
  Important Note: The fact that YOU (the student) disagree with the claim does not make it a weakness. It must be a claim that is questionable or unsupported in the context of the argument.
  
  Example: "We must invest heavily in nuclear power because clean energy sources are the only way forward." (Weakness: The argument relies on the unsupported assumption that nuclear power is universally accepted as a 'clean energy source'.)
  Impact: If the reader rejects the unsupported claim or assumption, the entire conclusion collapses.

4. Appeals

Arguments often appeal to external factors (like authority or emotion). This is only a weakness if the appeal is inappropriate.

• Appeal: Arguments frequently appeal to authority, popularity, emotion, tradition, or novelty.
  
  When is it a weakness? An appeal is a weakness if it is irrelevant or disproportionate to the claim being made.
  
  Example of irrelevant appeal: "You must support this tax policy because your grandmother would have wanted it." (Appeal to tradition is irrelevant to the economic soundness of the policy.)
  Example of disproportionate appeal: "If we don't fix the pothole immediately, countless innocent children will be injured and die in traffic accidents." (Disproportionate appeal to emotion regarding a minor issue.)
  Impact: Irrelevant or emotional appeals distract from logical considerations, failing to provide genuine justification.

5. Analogy

Analogies are tools, but bad tools break the argument.

• Analogy: An analogy is a comparison used to strengthen an argument.
  
  When is it a weakness? A wild analogy which lacks significant points of similarity constitutes a weakness. (Imperfect analogies can still strengthen an argument; only those that are totally inappropriate are weaknesses).
  Example: Arguing that "The economy is like a bicycle: if you stop pedaling (spending), you fall over." (Weakness: The analogy is wild because the economy has far more complex mechanisms than a simple bicycle.)
  Impact: If the comparison is too weak or too dissimilar, it provides no genuine illumination or support for the argument.

6. Responding to Counter-Arguments

A strong argument anticipates opposition.

• Responding to Counter: It is a weakness if the proponent fails to foresee and respond to an obvious objection to a claim or line of reasoning.
  
  Did you know? An argument is allowed to be one-sided! A proponent of a view is not obligated to show balance. However, they must address any counter-argument that is immediately obvious or central to the debate.
  Example: An argument proposes a new tax that will raise millions but fails to mention or address the obvious counter-objection that it will affect low-income families disproportionately.
  Impact: Failing to address an obvious counter-point demonstrates that the argument is incomplete, vulnerable, and has not considered the full scope of the issue.

Don't worry if this seems tricky at first! Evaluating reasoning takes practice. The key is to always ask: "Does the conclusion truly follow from the reasons, and are those reasons themselves solid and fully supported?" Good luck!