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.
Definitions And Concepts
What Definitions Are For
Introduces the purposes of definitions and why not every context calls for the same kind of definition, establishing the habit of asking 'what is this definition trying to do?' before evaluating it.
Focus on understanding the core distinction first, then use the examples to see how the idea behaves in actual arguments.
Start Here
What this lesson is helping you do
Introduces the purposes of definitions and why not every context calls for the same kind of definition, establishing the habit of asking 'what is this definition trying to do?' before evaluating it. The practice in this lesson depends on understanding Definiendum, Definiens, Function of a Definition, and Kinds of Definitions and applying tools such as Fit the Definition to Its Purpose and Avoid Circularity and Obscurity correctly.
How to approach it
Focus on understanding the core distinction first, then use the examples to see how the idea behaves in actual arguments.
What the practice is building
You will put the explanation to work through classification practice, quiz, analysis practice, diagnosis 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
Classify 10 definitions by function and type, and explain why each type fits or fails the context.
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 example 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.
Orientation
Definitions do different jobs
A definition is not just a sentence that tells you what a word means. In logic, definitions can report ordinary usage, fix a temporary rule, sharpen a vague boundary, or support a theoretical explanation. The right definition depends on the job the definition needs to do.
That is why the same term may be defined differently in a classroom policy, a legal code, a scientific theory, and an everyday conversation. You should not assume those differences show confusion. Often they show that the context has changed, and the definition has been adapted to serve a new function.
What to look for
- Ask what practical or conceptual job the definition is doing.
- Do not evaluate every definition as if it were a dictionary entry.
- Notice whether the context demands ordinary usage, precision, or theory.
Definitions should be judged partly by whether they fit the task they are meant to perform.
Core idea
The same term can need different levels of precision
In ordinary conversation, a loose definition may be perfectly acceptable. In a scholarship policy, medical guideline, or legal rule, the same term may need a much sharper boundary. Precision is not automatically better; it is better when the context requires it.
This is why precising definitions matter. They tighten a vague term for a practical reason, such as deciding eligibility or setting a measurable threshold. A strong analyst explains why that added precision is needed instead of merely noticing that the wording changed.
What to look for
- Compare the stakes of the context before judging the amount of precision needed.
- Ask whether the definition must guide classification, policy, or explanation.
- Be ready to explain why a looser or sharper wording would change the outcome.
Good definitions match their level of precision to the stakes of the context.
What to notice
Neutral clarification is different from persuasive framing
Some definitions are designed to influence attitude rather than clarify a concept. A persuasive definition loads the target term with approval or disapproval, often making it sound more noble or more suspect than a neutral definition would. 'Freedom fighter' versus 'insurgent' is the classic example — the same people, different framings.
That does not mean persuasive definitions are impossible to understand. It means they should be recognized for what they are. If the task is neutral conceptual analysis, persuasive wording is often a defect because it pushes evaluation before the concept itself has been clarified.
What to look for
- Notice emotionally loaded language in the definiens.
- Ask whether the wording clarifies the term or nudges an attitude.
- Separate rhetorical force from conceptual precision.
A definition can sound powerful while still doing a poor job of clarifying the concept.
Before you practice
Use a simple routine before classifying a definition
Start by naming the target term. Then ask what the definition is supposed to accomplish in its context. Next, identify the type of definition that best matches that function. Finally, decide whether the wording actually succeeds at that task.
This routine will keep your analysis from becoming a guessing game based on familiar labels. It also prepares you for later lessons where you will test definitions for scope, circularity, and practical adequacy.
What to look for
- Identify the term being defined before you judge the wording.
- Name the function before naming the definition type.
- Explain why the chosen type does or does not fit the context.
Strong definition analysis moves from function to type, and only then to evaluation.
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.
Definiendum
The term being defined — the word or phrase whose meaning the definition is trying to clarify.
Why it matters: Distinguishing the definiendum from the definiens is the basic vocabulary of definition analysis.
Definiens
The part of the definition that does the defining — the explanation or account that supplies meaning to the definiendum.
Why it matters: The definiens is where circularity, obscurity, and scope problems live.
Function of a Definition
The job a definition is intended to perform in a specific context, such as reporting usage, sharpening a concept, or fixing a technical meaning.
Why it matters: A definition should be judged partly by whether it serves the right purpose for its context.
Kinds of Definitions
Different categories of definitions such as lexical, stipulative, precising, theoretical, and persuasive, each suited to different tasks.
Why it matters: Different kinds of definitions are appropriate in different contexts; no single type is 'the right kind.'
Reference
Open these only when you need the extra structure
How the lesson is meant to unfold
Hook
A motivating question or contrast that frames why this lesson matters.
Concept Intro
The core idea is defined and separated from nearby confusions.
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.
Fit the Definition to Its Purpose
A good definition should be judged in light of whether it is lexical, stipulative, precising, theoretical, or persuasive, and whether that type fits the context.
Common failures
- A persuasive definition is used where neutral clarification is needed.
- A lexical definition is demanded where technical precision is required.
Avoid Circularity and Obscurity
A definition should clarify rather than merely repeat or obscure the target concept.
Common failures
- The definition uses the target term or a near-synonym without explanation.
- The wording is more obscure than the term being defined.
Check Scope and Border Cases
A definition should be tested against clear cases, excluded cases, and borderline cases to check for overbreadth and narrowness.
Common failures
- The definition is too broad and includes non-instances.
- The definition is too narrow and leaves out genuine instances.
Aim for Necessary and Sufficient Conditions
A rigorous definition should state conditions that are both necessary (every instance has them) and jointly sufficient (anything having them is an instance).
Common failures
- The definition states only a necessary condition, leaving some cases unclassified.
- The definition states only a sufficient condition, letting other instances slip through.
Patterns
Use these when you need to turn a messy passage into a cleaner logical structure before evaluating it.
Definition Analysis Schema
Input form
proposed_definition
Output form
definition_evaluation
Steps
- Identify the target term (definiendum).
- Identify the kind of definition being used.
- State the intended purpose or context.
- Check for circularity, overbreadth, narrowness, obscurity, and misuse.
- Test the definition against clear cases, excluded cases, and border cases.
- Revise the definition if needed.
Watch for
- Evaluating all definitions as if they had the same purpose.
- Ignoring whether the definition fits the intended scope.
Genus-and-Differentia Builder
Input form
target_concept
Output form
structured_definition
Steps
- Identify the broader class to which the thing belongs.
- Identify the distinguishing feature that sets it apart from other members of that class.
- Draft the definition in one sentence of the form 'An X is a Y that Z.'
- Test the definition against clear cases and borderline cases.
- Revise for scope and clarity.
Watch for
- Naming a differentia that is too broad to distinguish the target.
- Choosing a genus that is too remote or too narrow.
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
Defining 'Student' in Different Contexts
The best definition depends on what the definition is supposed to do. None of these three is wrong — each is fit for its purpose.
Lexical Use
A student is a person engaged in learning, especially at a school. (Reports ordinary usage.)
Precising Use
For purposes of scholarship eligibility, a student is any person carrying at least 12 credit hours per semester and in good academic standing. (Sharpens a vague term for practical classification.)
Stipulative Use
For this course's attendance policy, a 'student' is any person officially enrolled on the first day of the term. (Fixes a working meaning for a specific purpose.)
Pause and Check
Questions to use before you move into practice
Self-check questions
- What is this definition trying to accomplish?
- Would a different type of definition better fit this context?
- Is the wording doing real work or just stating a label?
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.
Classification Practice
FoundationsWhat Is This Definition Doing?
For each definition, identify the definiendum, state what job the definition is trying to do in its context, and name any mismatch between the definition and its purpose.
Four definitions in context
Focus on function first, type second.
Case 1 — Dictionary entry
Sibling (noun): a brother or sister; each of two or more children or offspring having one or both parents in common.
What is this definition trying to do? Which context is it serving?
Case 2 — Course policy
In this course, 'active participation' means contributing at least once per class session, either verbally in discussion or in writing via the online forum.
Is this reporting usage or fixing a rule for this course?
Case 3 — Political op-ed
Patriotism is the deep and principled love of one's country, distinguished from the empty flag-waving that shallow cynics mistake for it.
Does this clarify the concept or nudge attitude toward the writer's view?
Case 4 — Scientific paper
In this paper, we define 'moderate exercise' as sustained physical activity producing a heart rate between 50% and 70% of age-adjusted maximum, measured continuously over at least 30 minutes.
Why does the scientific context need this kind of precision?
Use one of the items above. State the target term, draft the definition you want to test, and explain whether it is too broad, too narrow, circular, or on target.
Quiz
FoundationsScenario Check: What Definitions Are For
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: "Judging a technical definition by ordinary-language standards alone." 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 identify definition function, starting from scratch. Be specific about each step and explain why the order matters.
Can the student transfer the skill of identify definition function to a genuinely new case?
Question 3 — Distinguish
Someone confuses definition function with definition type. 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 "Defining 'Student' in Different Contexts" 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 items above. State the target term, draft the definition you want to test, and explain whether it is too broad, too narrow, circular, or on target.
Analysis Practice
FoundationsApply the Concepts: What Definitions Are For
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: What Definitions Are For
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: What Definitions Are For
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 items above. State the target term, draft the definition you want to test, and explain whether it is too broad, too narrow, circular, or on target.
Analysis Practice
FoundationsDeep Practice: What Definitions Are For
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: What Definitions Are For
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: What Definitions Are For
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 items above. State the target term, draft the definition you want to test, and explain whether it is too broad, too narrow, circular, or on target.
Evaluation Practice
FoundationsPeer Review: What Definitions Are For
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: What Definitions Are For
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 items above. State the target term, draft the definition you want to test, and explain whether it is too broad, too narrow, circular, or on target.
Diagnosis Practice
FoundationsCounterexample Challenge: What Definitions Are For
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: What Definitions Are For
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: What Definitions Are For
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: What Definitions Are For
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: What Definitions Are For
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.
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
- Assuming that every good definition must be purely lexical.
- Evaluating function before identifying the definiendum.
Where students usually go wrong
Judging a technical definition by ordinary-language standards alone.
Ignoring the practical role the definition is supposed to serve.
Treating persuasive definitions as if they were neutral descriptions.
Historical context for this way of reasoning
Socrates
Socrates' relentless 'What is X?' questioning in the dialogues was aimed at forcing interlocutors past examples toward accounts of the essence of a thing. It is the ancestor of modern definition analysis.