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?
Application Strategy
Worked Examples
Problem Statement
A pharmaceutical company claims their new drug cures headaches within 10 minutes. They provide testimonials from 5 patients who felt better after taking it. Is this claim well-supported?
claimevidencefalse belief
Step 1
Identify the claim
The claim is that the drug cures headaches within 10 minutes. This is a specific, testable assertion.
Step 2
Examine the evidence
The only evidence provided is 5 patient testimonials. These are anecdotal — they are personal reports, not controlled data. There is no control group, no measurement of headache severity before and after, and no comparison to a placebo.
Step 3
Check the reasoning
Even if the patients truly felt better, feeling better after taking a drug does not prove the drug caused the improvement. Headaches often resolve on their own. Without a placebo-controlled trial, the claim is unsupported.
Step 4
Form a reasoned judgment
The claim is not well-supported. The evidence is weak (anecdotal, no controls), and the reasoning has a gap (post hoc fallacy — assuming the drug caused relief just because relief followed the drug). Stronger evidence — a randomised, placebo-controlled trial — is needed.
Problem Statement
Consider this argument: 'All metals conduct electricity. Copper is a metal. Therefore, copper conducts electricity.' Is this argument valid? Is it sound?
validityvalid argumentclaim
Step 1
Identify premises and conclusion
Premise 1: All metals conduct electricity. Premise 2: Copper is a metal. Conclusion: Copper conducts electricity.
Step 2
Test validity
Validity asks: if both premises were true, would the conclusion have to be true? Yes — if every metal conducts electricity and copper is a metal, then copper must conduct electricity. There is no scenario where both premises are true and the conclusion is false. The argument is valid.
Step 3
Test soundness
Soundness requires both validity and true premises. Premise 1 is true (all metals do conduct electricity). Premise 2 is true (copper is a metal). Since the argument is valid and both premises are true, it is sound.
Problem Statement
A student believes that studying the night before the test is the most effective strategy because they scored well on their last three tests doing exactly that. Evaluate this belief.
false beliefevidencereasoned judgment
Step 1
Identify the claim
The claim is that last-night studying is the most effective strategy. The word 'most' makes this a comparative claim — it asserts superiority over all other approaches.
Step 2
Examine the evidence
The evidence is personal experience: 3 tests with good scores after last-night study sessions. This is anecdotal evidence with a sample size of 3 and no comparison to alternative strategies.
Step 3
Identify reasoning flaws
Multiple issues exist. Post hoc reasoning assumes the studying caused the good scores without ruling out other factors (prior knowledge, easy tests, luck). Confirmation bias means the student notices successes and ignores failures. The claim 'most effective' is unsupported because no alternative strategies were tested.
Step 4
Reach a reasoned judgment
This is a false belief built on weak evidence and flawed reasoning. Research on learning consistently shows that spaced repetition over days or weeks produces stronger long-term retention than cramming. The student's personal experience does not override the broader body of evidence.
Problem Statement
Statement: 'Social media causes anxiety in teenagers.' Construct one argument supporting this statement and one argument against it.
argumentclaimevidencereasoned judgment
Step 1
Argue FOR the statement
Premise 1: Multiple peer-reviewed studies show a correlation between high social media use and increased self-reported anxiety in adolescents. Premise 2: Social media platforms use engagement algorithms that promote comparison and fear of missing out. Premise 3: Sleep disruption caused by late-night screen use is a documented contributor to anxiety. Conclusion: Social media use contributes to anxiety in teenagers.
Step 2
Argue AGAINST the statement
Premise 1: Correlation does not equal causation — anxious teenagers may simply spend more time on social media, not the other way around. Premise 2: Many teenagers use social media heavily without developing anxiety. Premise 3: Social media also provides social support, community, and access to mental health resources. Conclusion: The evidence does not establish that social media directly causes anxiety; the relationship is more complex.
Step 3
Form a reasoned judgment
Both arguments have merit. The evidence suggests a correlation, but causation is not firmly established. The most reasoned judgment is that social media may be a contributing factor among many, and its effect likely varies by individual, usage pattern, and content consumed. Oversimplifying to 'social media causes anxiety' is not fully supported by the evidence.
Memorize formulas
No formulas for this topic.
Review
1
Which of the following is the most accurate description of a logical argument?
Ans
A set of premises intended to support a conclusion
Review
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Define argument
An argument is a reasoned chain of thought: premises lead to a conclusion.
Premises → Conclusion
Eliminate incorrect options
Emotional appeals lack logical structure. A single factual statement has no supporting reasoning. A disagreement may contain no structured reasoning at all.
Option B is the definition of a logical argument.
2
A student claims that a herbal remedy cures the common cold because their grandmother used it and never got sick for more than two days. What is the primary flaw in this reasoning?
Ans
It relies on anecdotal evidence rather than controlled, systematic evidence
Review
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Identify the type of evidence
The student uses one person's experience as proof. This is anecdotal evidence.
Anecdotal evidence ≠ systematic evidence
Evaluate the flaw
Anecdotal evidence is subject to confirmation bias, confounding variables, and small sample size. The primary logical flaw is the type of evidence used.
The argument lacks properly controlled evidence.
3
Consider the following argument: "All mammals are warm-blooded. Whales are mammals. Therefore, whales are warm-blooded." What type of reasoning does this demonstrate?
Ans
Deductive reasoning from general principles
Review
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Identify the structure
General premise (all mammals → warm-blooded) + specific premise (whales → mammals) = conclusion.
General → Specific = Deductive
Classify the reasoning
Deductive reasoning moves from general principles to a specific, logically necessary conclusion.
This is a valid deductive argument.
4
Which of the following best defines the term 'claim' in critical thinking?
Ans
A statement that asserts something to be true, which can be supported or challenged
Review
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Define 'claim'
A claim is a declarative statement that something is true. It may be true or false — it needs evaluation.
Claim = assertion that may be supported or challenged
Distinguish from related concepts
A proven fact is a verified claim. An emotional response and a question are not claims.
Option A correctly defines 'claim'.
5
What does it mean for an argument to be 'valid' in formal logic?
Ans
The conclusion follows necessarily from the premises, regardless of whether the premises are true
Review
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Distinguish validity from truth
Validity concerns the logical connection between premises and conclusion, not the factual accuracy of the premises.
Valid = if premises true, then conclusion must be true
Evaluate options
Option A describes soundness (valid + true premises). Options C and D describe persuasion and popular opinion, not logical validity.
Option B is the definition of validity.
6
A person believes that drinking cold water after a meal causes cancer because they read it in a forwarded social media message. What is the most important step in critically evaluating this belief?
Ans
Checking whether the source provides verifiable, scientifically credible evidence
Review
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Identify the nature of the belief
The belief comes from an unverified social media source — a classic case of a potentially false belief.
Source credibility must be evaluated.
Apply critical evaluation
The gold standard is checking for verifiable, scientifically credible evidence such as peer-reviewed studies.
Verifiable evidence is required to assess truth.
7
An argument states: "If it rains, the ground gets wet. The ground is wet. Therefore, it rained." What is wrong with this argument?
Ans
It commits the fallacy of affirming the consequent — the ground could be wet for other reasons
Review
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Identify the logical form
If P → Q. Q. Therefore P. This is affirming the consequent.
Form: Affirming the consequent (invalid)
Explain why it fails
Q can be true for reasons other than P. Wet ground has multiple possible causes besides rain.
The conclusion does not necessarily follow.
8
Which of the following is an example of 'evidence' in the context of critical thinking?
Ans
Data from a peer-reviewed clinical trial showing a drug reduces symptoms in 70% of patients
Review
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Define evidence
Evidence is objective, verifiable information that can be used to support or refute a claim.
Evidence must be systematic and verifiable.
Evaluate each option
Clinical trial data is systematic and verifiable. The others are subjective, anecdotal, or based on popularity.
Option C is proper evidence.
9
What is the primary characteristic of a 'false belief' as discussed in critical thinking?
Ans
A belief held with confidence that is not supported by adequate evidence or logical reasoning
Review
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Define false belief
A false belief is a conviction held despite lack of adequate evidence or despite evidence to the contrary.
False belief = confident belief without adequate support
Eliminate distractors
Popularity, single experiments, and cultural factors are not the defining features of false beliefs.
Option B correctly identifies the key characteristic.
10
A reasoned judgment requires which of the following?
Ans
Weighing available evidence and reasoning logically before forming a conclusion
Review
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Define reasoned judgment
Reasoned judgment involves careful evaluation of evidence and logical analysis before reaching a conclusion.
Reasoned judgment = evidence + logic → conclusion
Contrast with alternatives
Majority opinion, simplicity, and authority are shortcuts that bypass the reasoning process.
Only Option A describes true reasoned judgment.
11
Consider: "All birds can fly. Penguins are birds. Therefore, penguins can fly." What does this argument demonstrate about the relationship between validity and truth?
Ans
The argument is valid but not sound, because one premise is factually false
Review
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Check validity (logical structure)
The form is: All A are B. C is A. Therefore C is B. This is a valid syllogistic form.
Structure is valid.
Check soundness (truth of premises)
Not all birds can fly (ostriches, penguins, kiwis). The first premise is false.
Valid but not sound.
12
A researcher finds that students who eat breakfast score higher on tests. They conclude that eating breakfast causes better test performance. What critical thinking skill is most needed to evaluate this conclusion?
Ans
Considering whether a third variable (such as sleep quality or study habits) could explain the correlation
Review
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Identify the logical flaw
Correlation between breakfast and test scores does not prove causation. This is a classic reasoning error.
Correlation ≠ Causation
Apply critical evaluation
A confounding (third) variable could explain both observations. Sleep quality, discipline, or socioeconomic status could influence both breakfast habits and academic performance.
Third-variable explanation must be considered.
13
Which of the following is an essential difference between a 'claim' and 'evidence'?
Ans
A claim is an assertion that may or may not be true, while evidence is the information used to support or refute it
Review
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Define both terms
Claim = assertion. Evidence = verifiable information supporting or refuting a claim.
Claim ≠ Evidence
Identify the relationship
Evidence is used to evaluate claims. They serve different roles in critical thinking.
Option C correctly distinguishes the two.
14
A teacher tells a student: "You should believe that climate change is real because 97% of scientists agree on it." While the statistic may be accurate, what is the logical weakness of this argument as presented?
Ans
It appeals to consensus rather than presenting the actual evidence and reasoning behind the conclusion
Review
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Identify the argument type
The argument appeals to the number of agreeing scientists rather than presenting the evidence directly.
Appeal to consensus
Assess the weakness
Consensus is an indicator, not proof. The stronger approach is to present the underlying evidence and reasoning.
Actual evidence would strengthen the argument.
15
Someone argues: "Premise 1: All metals expand when heated. Premise 2: Copper is a metal. Conclusion: Copper expands when heated." If Premise 1 were discovered to be false (some metal does not expand when heated), what would happen to the argument?
Ans
The argument remains valid in structure but becomes unsound because it has a false premise
Review
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Separate validity from soundness
Validity = logical structure is correct. Soundness = valid + all premises are true.
Validity ≠ Soundness
Apply to the argument
If Premise 1 is false, the structure remains valid but the argument is no longer sound.
Valid but unsound.
16
A person refuses to consider evidence that contradicts their existing belief about a medical treatment, only seeking information that confirms what they already think. Which critical thinking error does this demonstrate?
Ans
Confirmation bias — selectively seeking or accepting evidence that supports a pre-existing belief
Review
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Identify the pattern
The person selectively engages with confirming evidence and dismisses contradicting evidence.
Selective evidence processing
Name the bias
Confirmation bias is the tendency to favor information that confirms existing beliefs.
This is confirmation bias.
17
When constructing a logical argument to show that a statement is false, which approach is most rigorous?
Ans
Presenting contradictory evidence and demonstrating logical inconsistencies in the original claim
Review
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Identify the gold standard
Rigorous refutation requires addressing the claim directly with evidence and logical analysis.
Contradictory evidence + logical inconsistency
Evaluate alternatives
Expert disagreement, unpopularity, and being outdated are indirect indicators, not rigorous refutations.
Option B is the most rigorous approach.
18
What is the 'truth value' of a statement in critical thinking?
Ans
Whether the statement is true or false, independent of whether anyone believes it
Review
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Define truth value
Truth value is the property of a statement being either true or false in reality.
Truth value is objective, not subjective.
Distinguish from subjective measures
Feelings, popularity, and recency are subjective or social measures, not truth value.
Option D correctly defines truth value.
19
Which of the following demonstrates the best use of 'objective' reasoning in evaluating a health claim?
Ans
Reviewing multiple randomized controlled trials and comparing their findings before forming a conclusion
Review
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Define objective reasoning
Objective reasoning is based on verifiable evidence, minimizing personal bias.
Objective = evidence-based, bias-minimized
Evaluate each option
RCTs are the gold standard of objective evidence. The others rely on authority, anecdote, or popularity.
Option D demonstrates objective reasoning.
20
A student encounters the following argument: "No one has ever proven that ghosts do not exist. Therefore, ghosts exist." What is the logical error in this argument?
Ans
It shifts the burden of proof — the person making the claim (ghosts exist) must provide evidence, not demand disproof
Review
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Identify the fallacy
The argument uses lack of disproof as proof. This is an appeal to ignorance.
Appeal to ignorance (argumentum ad ignorantiam)
Explain the burden of proof
The person asserting a claim bears the burden of providing evidence. You cannot prove a claim by demanding others disprove it.
Burden of proof rests on the claimant.
Question 1 of 20
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1
Which of the following is the most accurate description of a logical argument?