Critical Thinking
Arguments, Claims, and Evidence
An argument is a set of statements where one or more premises are offered to support a claim. Every argument has two components: the evidence or reasons given, and the conclusion drawn from them. The strength of an argument depends on how well the premises actually support the conclusion.
Claim: A statement that asserts something is true or false. Every argument centres on one main claim, called the conclusion.
Premises: The reasons, facts, or data offered to justify the claim. An argument is only as strong as its premises.
Evidence: Specific, verifiable information — observations, experimental results, statistics, or documented facts — that backs up a premise. Strong evidence is objective and can be independently checked.
Distinguishing a claim from evidence is the first step in critical thinking. A claim states a position; evidence provides the grounds for accepting it. A well-constructed argument links evidence to the claim through clear, logical reasoning.
Direct evidence: Data that straightforwardly supports a claim — e.g., measuring a patient's temperature to confirm a fever.
Indirect (circumstantial) evidence: Facts that imply a claim is likely true without proving it directly — e.g., finding muddy footprints to infer someone walked through a garden.
Anecdotal evidence: Personal stories or isolated examples. These are weak forms of evidence because they are not systematic and cannot be generalised.
Evidence Strength Hierarchy (strongest to weakest)
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Peer-reviewed experimental data
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Systematic observations and measurements
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Expert consensus based on accumulated research
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Logical deduction from established facts
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Personal anecdotes and unverified reports
Validity and Truth Value
Validity refers to the logical structure of an argument — whether the conclusion truly follows from the premises. A valid argument guarantees that if the premises are true, the conclusion must also be true. Validity is about form, not content.
Valid argument: If all premises are true, the conclusion cannot be false. The logic connecting them is airtight.
Invalid argument: The conclusion does not logically follow from the premises, even if the premises happen to be true. There is a gap in the reasoning.
Sound argument: A valid argument whose premises are also actually true. Soundness combines both correct logic and true starting points.
Argument Quality Categories
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Valid + True premises → Sound (best)
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Valid + False premises → Valid but unsound
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Invalid + True premises → True conclusion by coincidence
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Invalid + False premises → Unreliable on every count
Every meaningful claim has a truth value — it is either true or false. Determining the truth value requires checking whether the claim corresponds to reality, which in turn requires evidence. A claim without evidence has an unknown truth value and should not be accepted.
True claim: Corresponds to verified facts and evidence. The statement matches observable reality.
False claim: Contradicts verified facts and evidence. The statement does not match observable reality.
Unverifiable claim: Cannot be tested or confirmed with available evidence. These should be treated with scepticism, not accepted as true.
Identifying and Evaluating False Beliefs
A false belief is a statement or idea that people accept as true but that contradicts evidence or sound reasoning. False beliefs spread when people accept claims without examining the evidence, rely on authority instead of proof, or let emotions override logic.
Unsubstantiated belief: A belief held without supporting evidence. It may turn out to be true, but there is no basis for accepting it yet.
Contradicted belief: A belief that available evidence directly disproves. Continuing to hold it requires ignoring or dismissing evidence.
Circular belief: A belief justified only by itself — e.g., 'This book is accurate because the book says so.' This provides no independent support.
Common Sources of False Beliefs
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Appeal to authority (accepting a claim because an authority figure says so, without evidence)
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Confirmation bias (seeking only information that supports what you already believe)
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Bandwagon effect (accepting a claim because many people believe it)
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Emotional reasoning (accepting a claim because it feels right)
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Post hoc reasoning (assuming that because B happened after A, A caused B)
Critically evaluating a belief means subjecting it to logical scrutiny: check whether there is evidence, whether the reasoning is valid, and whether the conclusion follows from the premises. This process separates reasoned judgment from unreflective acceptance.
Step 1 — Identify the claim: Pinpoint exactly what is being asserted. Vague claims are harder to evaluate.
Step 2 — Examine the evidence: Determine what evidence is offered and whether it is direct, indirect, or anecdotal.
Step 3 — Check the reasoning: Does the conclusion logically follow from the evidence, or are there gaps, fallacies, or unsupported leaps?
Step 4 — Consider alternatives: Could the same evidence support a different conclusion? Are there counterexamples?
Reasoned Judgment and Logical Arguments
A reasoned judgment is a conclusion reached after carefully weighing available evidence, applying logical rules, and considering alternative explanations. Unlike a snap opinion, it is deliberate, transparent, and open to revision when new evidence emerges.
Based on evidence, not emotion: Reasoned judgments set aside personal feelings and focus on what the evidence supports.
Transparent reasoning: The path from evidence to conclusion can be traced and evaluated by others.
Open to revision: If new, stronger evidence appears, a reasoned judgment can be updated. Stubbornness in the face of counter-evidence is the opposite of critical thinking.
Constructing a logical argument for or against a statement requires clearly stating the claim, providing premises backed by evidence, and ensuring the reasoning is valid. The ability to argue both sides of an issue is a hallmark of critical thinking.
Arguing FOR a statement: Present premises that, if true, make the conclusion necessarily or probably true. Support each premise with verifiable evidence.
Arguing AGAINST a statement: Show that the premises are false, the reasoning is invalid, or that counter-evidence exists. You do not need to prove the opposite — just that the original argument fails.
Straw man fallacy: A common error where one misrepresents the opposing argument to make it easier to attack. Critical thinkers engage with the strongest version of the opposing position.
Checklist for a Strong Logical Argument
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Is the claim stated clearly and specifically?
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Are all premises explicitly identified?
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Is each premise supported by credible evidence?
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Does the conclusion follow logically from the premises?
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Have counterarguments and alternative explanations been considered?
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Is the reasoning free of logical fallacies?