Read
Build the mental model
Move through the guided explanation first so the central distinction and purpose are clear before you evaluate your own work.
Fallacies And Errors
Deductive and Formal Fallacies
Examines fallacies driven by formal structure, quantifier scope, class reasoning, and invalid deductive patterns, and shows why these errors demand structural rather than evidential repair.
Read the explanation sections first, then use the activities to test whether you can apply the idea under pressure.
Start Here
What this lesson is helping you do
Examines fallacies driven by formal structure, quantifier scope, class reasoning, and invalid deductive patterns, and shows why these errors demand structural rather than evidential repair. The practice in this lesson depends on understanding Species of a Fallacy and Scope or Structure Failure and applying tools such as Trace the Species Back to the Family and Diagnose by the Mode of Reasoning correctly.
How to approach it
Read the explanation sections first, then use the activities to test whether you can apply the idea under pressure.
What the practice is building
You will put the explanation to work through diagnosis practice, quiz, analysis practice, comparison exercise, rapid identification, evaluation practice, and argument building activities, so the goal is not just to recognize the idea but to use it under your own control.
What success should let you do
Diagnose 10 deductive fallacies and explain the violated structure and repair for each.
Reading Path
Move through the lesson in this order
The page is designed to teach before it tests. Use this sequence to keep the reading, examples, and practice in the right relationship.
Study
Watch the move in context
Use the worked examples to see how the reasoning behaves when someone else performs it carefully.
Do
Practice with a standard
Only then move into the activities, using the pause-and-check prompts as a final checkpoint before you submit.
Guided Explanation
Read this before you try the activity
These sections give the learner a usable mental model first, so the practice feels like application rather than guesswork.
Core distinction
What makes a fallacy formal
A formal fallacy is one you can detect purely from the shape of the argument, without knowing whether any particular premise is true. If the form is invalid, no amount of true premises can rescue the inference. This is what makes formal fallacies especially dangerous: they can be built out of perfectly plausible sentences and still fail.
Contrast this with an informal fallacy, where the problem usually involves content, context, or evidence. A formal fallacy is a structural defect, so the repair is structural: you must change the form of the argument, not merely swap in better premises.
What to look for
- Ask whether the argument would be bad even if all the premises happened to be true.
- Check the form by substituting letters for content.
- Remember that better evidence cannot rescue an invalid form.
Formal fallacies are defects of shape; you fix them by changing the shape.
Pattern family
Conditional-form fallacies
The most common formal fallacies involve misusing if-then statements. Affirming the consequent takes 'If P then Q' and 'Q' and jumps to 'P'. But Q could be true for many reasons unrelated to P, so the inference is invalid. Denying the antecedent takes 'If P then Q' and 'not P' and jumps to 'not Q', which makes the same mistake in reverse: P is not the only possible route to Q.
The valid counterparts are modus ponens (affirm the antecedent, conclude the consequent) and modus tollens (deny the consequent, conclude the negation of the antecedent). The difference between the valid and invalid patterns is entirely structural. You can learn to spot them by mapping the sentences to P and Q and checking the pattern.
What to look for
- Label each conditional statement with clear P and Q roles.
- Check which of P, Q, not-P, or not-Q is being affirmed.
- Match the move to modus ponens or modus tollens — anything else is invalid.
If the second premise affirms Q or denies P, the argument is probably fallacious.
Pattern family
Categorical and term-structure fallacies
Categorical syllogisms have their own formal errors. The undistributed middle fails because the middle term never refers to the whole of its class, so it cannot connect the other two terms. Illicit major and illicit minor occur when a term is distributed in the conclusion but not in the premise that should justify that scope.
These errors look different from conditional-form fallacies, but they come from the same underlying idea: the conclusion attempts to go beyond what the form actually supports. Diagnosing them requires checking distribution and term roles rather than just feeling whether the argument 'sounds right'.
What to look for
- Identify the major, minor, and middle terms.
- Check whether each term's distribution in the conclusion is justified by the premises.
- Look for a middle term that never actually gets distributed.
Categorical fallacies are about terms that overreach their support.
Pattern family
Linguistic and scope fallacies
Not every formal fallacy is about connectives or categorical terms. Equivocation uses one word in two different senses inside the same argument. Amphiboly exploits ambiguous grammatical structure. Quantifier-scope confusion mixes up 'some X are Y' with 'everything is Y' or 'everyone has the same friend' with 'everyone has at least one friend'.
These errors are structural in a broader sense: they depend on the logical form that the sentences are supposed to express, and they fail when the intended form is read incorrectly. A good diagnosis shows the two readings explicitly and identifies which one is needed for the inference to work.
What to look for
- Look for any word that appears in two different senses.
- Check whether the sentence has more than one grammatical parse.
- Paraphrase each quantified claim carefully to pin down its scope.
Scope and linguistic fallacies hide inside ambiguous phrases; the fix is clearer form.
Core Ideas
The main concepts to keep in view
Use these as anchors while you read the example and draft your response. If the concepts blur together, the practice usually blurs too.
Species of a Fallacy
A more specific recurring error pattern that instantiates a broader fundamental inferential defect.
Why it matters: Species help learners see both the named error and its deeper structure.
Scope or Structure Failure
A family of errors caused by misreading logical form, quantifier scope, class structure, or formal relation.
Why it matters: This family is central to deductive and definitional reasoning.
Reference
Open these only when you need the extra structure
How the lesson is meant to unfold
Concept Intro
The core idea is defined and separated from nearby confusions.
Rule Or Standard
This step supports the lesson by moving from explanation toward application.
Worked Example
A complete example demonstrates what correct reasoning looks like in context.
Guided Practice
You apply the idea with scaffolding still visible.
Assessment Advice
Use these prompts to judge whether your reasoning meets the standard.
Mastery Check
The final target tells you what successful understanding should enable you to do.
Reasoning tools and formal patterns
Rules and standards
These are the criteria the unit uses to judge whether your reasoning is actually sound.
Trace the Species Back to the Family
A correct fallacy diagnosis should identify both the specific named error and the broader inferential defect it exemplifies.
Common failures
- The learner memorizes labels without understanding the violated standard.
- Two fallacies are treated as unrelated even though they share the same deeper defect.
Diagnose by the Mode of Reasoning
The same surface error term may need different analysis depending on whether the reasoning is deductive, inductive, abductive, Bayesian, or practical.
Common failures
- A probabilistic error is judged as though it were purely deductive.
- A problem-solving failure is mislabeled with a rhetorical fallacy name while ignoring strategic structure.
Repair Rather Than Merely Label
A strong fallacy analysis should explain what inferential repair would be required for the argument to meet the relevant standard.
Common failures
- The fallacy is named but not explained.
- No corrected version of the reasoning is offered.
Charitable Reading Before Fallacy Accusation
Before diagnosing a fallacy, reconstruct the strongest plausible version of the argument and check whether the error survives that reconstruction.
Common failures
- Attacking a careless phrasing instead of the best version of the argument.
- Declaring a fallacy prematurely without checking for an implicit premise that would rescue the reasoning.
Patterns
Use these when you need to turn a messy passage into a cleaner logical structure before evaluating it.
Fallacy Taxonomy Map
Input form
argument_or_reasoning_case
Output form
family_species_repair_analysis
Steps
- Identify the mode of reasoning involved.
- State the standard that should govern the case.
- Determine the fundamental fallacy family violated.
- Identify the most specific species if one applies.
- State how the reasoning would need to be repaired.
Watch for
- Naming a species without identifying the violated standard.
- Using a familiar fallacy label when the deeper defect is actually different.
Cross-Mode Fallacy Comparison
Input form
paired_reasoning_cases
Output form
shared_family_different_species_analysis
Steps
- Identify the reasoning mode in each case.
- State the governing standard for each case.
- Identify the shared fundamental family.
- Explain how the species differ by context.
- Compare the repairs required.
Watch for
- Assuming identical labels imply identical structure.
- Ignoring that mode-specific standards shape what counts as an error.
Worked Through
Examples that model the standard before you try it
Do not skim these. A worked example earns its place when you can point to the exact move it is modeling and the mistake it is trying to prevent.
Worked Example
Deductive Species Under Scope and Structure Failure
These species differ in form, but they all arise from structural failure rather than mere weak evidence. The repair is always to fix the form.
Species Map
Invalid Conditional Form
- affirming the consequent
- denying the antecedent
Linguistic Or Scope Failure
- equivocation
- amphiboly
- quantifier scope confusion
- composition
- division
Term Or Class Structure Failure
- undistributed middle
- illicit major
- illicit minor
- exclusive premises
Worked Example
Affirming the Consequent: a walk-through
Repair
Either (a) weaken the conclusion from 'therefore' to 'there is some evidence that', which makes the argument inductive rather than deductive, or (b) add a premise ruling out other causes, for example 'The sprinklers did not run and there was no dew.'
Analysis
The argument has the form: If P then Q. Q. Therefore P. This is invalid because there are many things that could make the grass wet — sprinklers, a dew-heavy morning, a neighbor's hose. Q does not guarantee P because P is not the only possible cause of Q.
Argument
If it rained last night, the grass would be wet. The grass is wet. Therefore it rained last night.
Pause and Check
Questions to use before you move into practice
Self-check questions
- What formal standard is violated here?
- Is the problem one of connective form, term distribution, or scope?
- Would the argument be invalid even if every premise were true?
Practice
Now apply the idea yourself
Move into practice only after you can name the standard you are using and the structure you are trying to preserve or evaluate.
Diagnosis Practice
DeductiveDiagnose the Formal Failure
For each argument, identify the formal fallacy (or say 'valid'), map the argument to its logical form, and explain what structural change would be needed to repair it.
Six formal-reasoning cases
Translate each into schematic form before diagnosing. Some are valid — do not force a fallacy diagnosis on those.
Case 1
If the bridge had failed, the sensors would report pressure spikes. The sensors are reporting pressure spikes. So the bridge has failed.
Map to If P then Q form and check the move.
Case 2
If the defendant were at the scene, her prints would be on the counter. Her prints are not on the counter. Therefore she was not at the scene.
Check whether this is modus tollens or something else.
Case 3
Some politicians are lawyers. Some lawyers are criminals. Therefore some politicians are criminals.
What is the middle term, and is it ever distributed?
Case 4
Nothing is better than a day on the lake. Even a bad day at work is better than nothing. So a bad day at work is better than a day on the lake.
Where does the word 'nothing' shift meaning?
Case 5
Everyone in the study group has a study partner. So there is one person who is the study partner of everyone in the group.
What is the scope of the existential and the universal?
Case 6
Every cell in a human body is microscopic. Therefore the human body is microscopic.
Does a property of parts transfer to the whole?
Proof Draft
LineStatementJustificationAction
1
2
3
Quiz
FoundationsScenario Check: Deductive and Formal Fallacies
Each question presents a scenario or challenge. Answer in two to four sentences. Focus on showing that you can use what you learned, not just recall it.
Scenario questions
Work through each scenario. Precise, specific answers are better than long vague ones.
Question 1 — Diagnose
A student makes the following mistake: "Calling every bad argument 'non sequitur' without more analysis." Explain specifically what is wrong with this reasoning and what the student should have done instead.
Can the student identify the flaw and articulate the correction?
Question 2 — Apply
You encounter a new argument that you have never seen before. Walk through exactly how you would diagnose formal failure, starting from scratch. Be specific about each step and explain why the order matters.
Can the student transfer the skill of diagnose formal failure to a genuinely new case?
Question 3 — Distinguish
Someone confuses scope structure failure with fallacy species. Write a short explanation that would help them see the difference, and give one example where getting them confused leads to a concrete mistake.
Does the student understand the boundary between the two concepts?
Question 4 — Transfer
The worked example "Deductive Species Under Scope and Structure Failure" showed one way to handle a specific case. Describe a situation where the same method would need to be adjusted, and explain what you would change and why.
Can the student adapt the demonstrated method to a variation?
Use one of the sentences above and move carefully from ordinary language to a clearer predicate-logic style representation.
Analysis Practice
FoundationsApply the Concepts: Deductive and Formal Fallacies
Analyze each passage below using the concepts from this lesson. Identify key logical features and explain your reasoning.
Practice scenarios
Work through each scenario carefully. Apply the concepts from this lesson.
Scenario 1
A local council argues: every park that has been surveyed shows declining bird populations. The marsh reserve has not been surveyed. Therefore, we cannot conclude anything about its bird population.
Scenario 2
The professor told the class: 'Either your hypothesis is testable, or it does not belong in a scientific paper.' Maria's hypothesis predicts no observable outcomes.
Scenario 3
A fitness study concludes that runners who stretch before exercise report fewer injuries. However, runners who stretch may also be more cautious in other ways.
Pick one of the passages above and map how the reasons are supposed to support the conclusion.
Diagnosis Practice
FoundationsSpot the Error: Deductive and Formal Fallacies
Each passage contains a logical mistake. Identify the error, name it if possible, and explain why the reasoning fails.
Practice scenarios
Work through each scenario carefully. Apply the concepts from this lesson.
Case A
Everyone at the meeting agreed the policy is fair. Since the meeting was open to the public, we can say the public agrees the policy is fair.
Case B
No reptile is a mammal. No mammal is an insect. Therefore, no reptile is an insect.
Case C
The forecast said 70% chance of rain. It did not rain. Therefore, the forecast was wrong.
Use one of the passages above. Name the weakness, explain the violated standard, and show how the reasoning should be repaired.
Comparison Exercise
FoundationsCompare and Connect: Deductive and Formal Fallacies
Compare the reasoning in the passages below. Identify similarities, differences, and which argument is stronger, explaining your criteria.
Practice scenarios
Work through each scenario carefully. Apply the concepts from this lesson.
Argument X
Since all observed swans in Europe were white, all swans are white.
Argument Y
Since the chemical formula for water is H2O in every sample we have tested, water is H2O.
Argument Z
Since every student I asked preferred online classes, all students prefer online classes.
Use one of the sentences above and move carefully from ordinary language to a clearer predicate-logic style representation.
Analysis Practice
FoundationsDeep Practice: Deductive and Formal Fallacies
Apply the concepts from this lesson to more complex scenarios. Work through each carefully and explain your reasoning in full.
Advanced practice scenarios
Each scenario tests your ability to apply foundational logic concepts in realistic contexts.
Case 1
An editorial argues: 'Standardized testing must be eliminated because it causes student anxiety. And since anything that causes anxiety is harmful, standardized testing is harmful.' Analyze the argument's structure, identify any hidden premises, and evaluate its strength.
Case 2
A scientist writes: 'We observed that 90% of treated mice recovered, while only 30% of untreated mice recovered. The treatment appears effective. However, the treated group was also younger on average.' Identify the argument, the potential confounder, and what additional information would strengthen or weaken the conclusion.
Case 3
A philosopher claims: 'Either free will is an illusion, or moral responsibility is justified. Neuroscience has shown that brain activity precedes conscious decisions. Therefore, free will is probably an illusion, and moral responsibility may not be justified.' Map the logical structure and evaluate whether the conclusion follows.
Pick one of the passages above and map how the reasons are supposed to support the conclusion.
Analysis Practice
FoundationsReal-World Transfer: Deductive and Formal Fallacies
Apply what you have learned to these real-world contexts. Analyze each scenario using the tools and concepts from this lesson.
Transfer practice
Connect the concepts from this lesson to contexts outside the classroom.
Media literacy
A social media post claims: 'A new study proves that video games improve intelligence.' The post links to a study of 40 college students who played puzzle games for 2 weeks and showed improved scores on one type of spatial reasoning test. Evaluate this claim using what you know about arguments, evidence, and reasoning.
Everyday reasoning
A friend argues: 'I should not get vaccinated because my cousin got vaccinated and still got sick. Also, I read an article that said natural immunity is better.' Identify the types of reasoning, assess their strength, and explain what additional evidence would be relevant.
Professional context
A manager says: 'Our last three hires from University X performed well, so we should recruit exclusively from University X.' Analyze the reasoning type, identify potential problems, and suggest a better approach.
Pick one of the passages above and map how the reasons are supposed to support the conclusion.
Rapid Identification
FoundationsTimed Drill: Deductive and Formal Fallacies
Work through these quickly. For each passage, identify whether it contains an argument, name its type if so, and point to the conclusion. Aim for speed and accuracy.
Quick-fire argument identification
For each item, decide: argument or not? If yes, what type and what is the conclusion? Under 45 seconds per item.
Item 1
The bridge was built in 1962. It was designed by a local engineering firm and cost $2.3 million.
Item 2
Because the experiment was not replicated, the results should be treated with caution.
Item 3
Sharks have survived five mass extinction events, so they are remarkably resilient species.
Item 4
If the evidence was obtained illegally, the court must exclude it. The evidence was obtained without a warrant. Warrantless searches are illegal. Therefore, the court must exclude the evidence.
Item 5
The town council meets every second Tuesday. This week is the second Tuesday. The library will be used for the meeting.
Item 6
The most likely reason the power went out is the thunderstorm, since the outage started exactly when lightning struck the transformer.
Use one of the sentences above and move carefully from ordinary language to a clearer predicate-logic style representation.
Evaluation Practice
FoundationsPeer Review: Deductive and Formal Fallacies
Below are sample student attempts to identify and analyze arguments. Evaluate each response: Is the identification correct? Is the analysis accurate? What feedback would you give?
Evaluate student argument analyses
Each student tried to break down an argument into premises and conclusion. Assess their work.
Student A's work
Passage: 'Since exercise reduces stress and stress causes health problems, exercise prevents health problems.' Student A wrote: 'Premise 1: Exercise reduces stress. Premise 2: Stress causes health problems. Conclusion: Exercise prevents health problems. This is a valid deductive argument.'
Student B's work
Passage: 'The committee should approve the budget because it was prepared by experts.' Student B wrote: 'This is not an argument. It is just a recommendation.'
Student C's work
Passage: 'Most doctors recommend regular check-ups. Regular check-ups catch diseases early. Early detection saves lives. Therefore, you should get regular check-ups.' Student C wrote: 'Premise 1: Most doctors recommend check-ups. Conclusion: You should get check-ups. This is an inductive argument from authority.'
Student D's work
Passage: 'It will probably rain tomorrow because the barometric pressure is dropping and clouds are moving in from the west.' Student D wrote: 'Premise 1: Barometric pressure is dropping. Premise 2: Clouds are moving in. Conclusion: It will probably rain. This is an inductive argument based on observed indicators. Strength: moderate, since weather patterns are not perfectly predictable.'
Choose one of the passages above and evaluate it using the right standard for its reasoning mode.
Argument Building
FoundationsConstruction Challenge: Deductive and Formal Fallacies
Build arguments from scratch. For each task, construct a well-structured argument with clear premises and a conclusion. Identify the reasoning type you are using.
Construct original arguments
For each prompt, build a complete argument from scratch. Clearly state premises, conclusion, and reasoning type.
Task 1
Construct a deductive argument with two premises that concludes: 'This substance is not an acid.' Make sure the argument is valid.
Task 2
Build an inductive argument with at least three pieces of evidence supporting the conclusion: 'Regular reading improves vocabulary.' Make it as strong as you can.
Task 3
Construct an argument that uses an indicator word for the conclusion and a different indicator word for at least one premise. The topic should be about environmental policy.
Task 4
Build two different arguments for the same conclusion: 'Public libraries should remain publicly funded.' One argument should be deductive, the other inductive. Explain why one might be more persuasive than the other.
Use one of the sentences above and move carefully from ordinary language to a clearer predicate-logic style representation.
Diagnosis Practice
FoundationsCounterexample Challenge: Deductive and Formal Fallacies
For each argument, construct a counterexample or identify a scenario that shows the reasoning is flawed. Explain what the counterexample reveals about the argument's weakness.
Counterexamples and edge cases
Each argument has a flaw. Expose it with a specific counterexample.
Argument 1
Every time I have washed my car, it rained the next day. Therefore, washing my car causes rain.
Argument 2
No one at the party complained about the food. Therefore, everyone enjoyed the food.
Argument 3
This policy worked well in Sweden. Therefore, it will work well in Brazil.
Argument 4
The candidate won 60% of the vote in the primary. Therefore, they will win the general election.
Argument 5
All the reviews on the website are positive. Therefore, the product is excellent.
Use one of the passages above. Name the weakness, explain the violated standard, and show how the reasoning should be repaired.
Analysis Practice
FoundationsIntegration Exercise: Deductive and Formal Fallacies
These exercises connect the concepts from this lesson to ideas across different reasoning domains. Apply foundational concepts to scenarios that require multiple analytical tools.
Cross-cutting foundational exercises
Each scenario tests your ability to apply foundational logic concepts alongside other analytical skills.
Scenario 1
A news article reports: 'Scientists have proven that coffee is good for you, according to a new study of 500 adults who drink coffee daily.' Identify all arguments in this claim, classify the reasoning type(s), evaluate the evidence quality, and explain what additional information would be needed.
Scenario 2
A school board argues: 'Since standardized test scores are the best measure of student learning, and our test scores have risen 10% this year, our educational quality has improved.' Identify the premises and conclusion, classify the reasoning, spot any hidden assumptions, and construct an alternative explanation for the score increase.
Scenario 3
A city planner argues: 'If we build more bike lanes, more people will bike. More biking reduces car traffic. Less car traffic means less pollution. Therefore, building bike lanes will reduce pollution.' Map the argument structure, evaluate each inferential step separately (some may be deductive, others inductive), and identify the weakest link.
Scenario 4
An investor reasons: 'This company's stock has risen every year for the past eight years. The CEO is talented and the industry is growing. I should invest heavily.' Identify all reasoning types present, evaluate each one, and explain how the different types of reasoning interact in this argument.
Pick one of the passages above and map how the reasons are supposed to support the conclusion.
Diagnosis Practice
FoundationsMisconception Clinic: Deductive and Formal Fallacies
Each item presents a common misconception about arguments, reasoning, or logic. Identify the misconception, explain why it is wrong, and state the correct principle.
Common logic misconceptions
Diagnose and correct each misconception about basic logic and arguments.
Misconception 1
A student says: 'An argument with true premises must have a true conclusion.'
Misconception 2
A student claims: 'If two people disagree, at least one of them must be using bad logic.'
Misconception 3
A student writes: 'Opinions cannot be arguments because arguments require facts, not opinions.'
Misconception 4
A student argues: 'A strong argument is one that is persuasive. If people are convinced by it, it must be a good argument.'
Misconception 5
A student says: 'An explanation and an argument are the same thing -- both provide reasons for something.'
Use one of the passages above. Name the weakness, explain the violated standard, and show how the reasoning should be repaired.
Analysis Practice
FoundationsScaffolded Analysis: Deductive and Formal Fallacies
Build an argument analysis in stages. Each task provides a passage and walks you through the analysis process step by step. Complete each stage before moving on.
Step-by-step argument analysis
Analyze each argument progressively, one skill at a time.
Scaffold 1
Passage: 'Because violent crime has increased 15% this year and the police budget was cut 10% last year, the budget cuts are responsible for the crime increase. Therefore, the city council should restore police funding.' Stage 1: Identify all premises and the conclusion. Stage 2: Classify the reasoning type. Stage 3: Identify any hidden premises or assumptions. Stage 4: Evaluate the strength of the inference. Stage 5: Suggest what additional evidence would strengthen or weaken this argument.
Scaffold 2
Passage: 'Three out of four dentists recommend this toothpaste. Since expert opinion is reliable, you should use this toothpaste. After all, if experts recommend something, it must be good.' Stage 1: Put the argument in standard form. Stage 2: Identify the reasoning type for each inferential step. Stage 3: Spot any logical errors or questionable assumptions. Stage 4: Rewrite the argument to make it stronger.
Scaffold 3
Passage: 'Countries that invest in education have stronger economies. Our country should invest more in education to strengthen the economy. This is proven by the examples of South Korea, Finland, and Singapore.' Stage 1: Map the argument structure. Stage 2: Identify whether this is primarily deductive, inductive, or abductive. Stage 3: Evaluate the evidence. Stage 4: Identify the strongest objection to this argument. Stage 5: Revise the argument to address that objection.
Pick one of the passages above and map how the reasons are supposed to support the conclusion.
Analysis Practice
FoundationsSynthesis Review: Deductive and Formal Fallacies
These exercises combine everything you have learned about arguments, reasoning types, and evaluation. Each scenario requires you to identify, classify, analyze, evaluate, and improve an argument.
Comprehensive foundations review
Apply all foundational logic skills together.
Comprehensive 1
A school district superintendent argues: 'Our district should adopt year-round schooling. Studies show students in year-round schools retain 10% more knowledge. Teachers in year-round districts report higher job satisfaction. The only objection is tradition, but tradition is not a good reason to hold back progress. Other districts that switched have seen rising test scores within two years.' Perform a complete analysis: identify all premises and the conclusion, classify each reasoning step, find any hidden assumptions, spot any logical errors, evaluate the overall strength, and rewrite the argument to make it stronger.
Comprehensive 2
A debate transcript: Speaker A says 'Social media causes depression -- the data is clear.' Speaker B responds 'That is correlation, not causation. Besides, my teenagers use social media constantly and they are perfectly happy.' Speaker A replies 'Your children are exceptions. The overall trend is undeniable.' Analyze each speaker's reasoning: identify argument types, evaluate their strength, identify logical errors, find hidden assumptions, and draft what a well-reasoned third speaker should say.
Pick one of the passages above and map how the reasons are supposed to support the conclusion.
Argument Mapper
Build an argument diagram by adding premises, sub-conclusions, and a conclusion. Link nodes to show which claims support which.
Add nodes above, or load a template to get started. Each node represents a proposition in your argument.
■ Premise■ Sub-conclusion■ Conclusion
Animated Explainers
Step-by-step visual walkthroughs of key concepts. Click to start.
Read the explanation carefully before jumping to activities!
Further Support
Open these only if you need extra help or context
Mistakes to avoid before submitting
- Describing a deductive failure as though it were just weak evidence.
- Skipping the structural repair step.
Where students usually go wrong
Calling every bad argument 'non sequitur' without more analysis.
Treating affirming the consequent as a mere probability error rather than a formal one.
Ignoring whether the defect is conditional, categorical, or quantificational.
Historical context for this way of reasoning
Aristotle
Aristotle distinguished fallacies 'in diction' (linguistic) from fallacies 'outside diction' (about things). That split survives in the modern contrast between equivocation-type fallacies and structural ones like affirming the consequent.