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Resting an argument on an expert is good practice; resting it on a famous name is not, and the difference is the subject of the question.
Paper packet. Every task here also exists on screen, where it is checked automatically; answers written on paper are not assessed by Nydus. When you are back at a device, enter your answers there.
You will take an argument that rests on what somebody said and decide whether that person's word is evidence here, by naming the subject the question belongs to and the subject the person is trained in and seeing whether they are the same. You will do it in both directions: marking the step that leans on the wrong person, and leaving alone the step that leans on the right one.
The parish meets on Friday to decide whether to shut the footbridge over the beck while it is repaired.
Shutting it puts a mile on the walk to the school and the shop for everyone on the far side.
A structural engineer walked the bridge in March and measured two cracked beams.
She says a bridge with those beams should not carry people through another winter.
A gardener from a television program has lived beside the beck for forty years and is well known in the village.
He says the bridge is as solid as the day it was built and the parish is wasting its money.
A builder who would be paid to do the work says the whole bridge needs replacing rather than repairing.
He has not been under the bridge and is going by the photographs in the engineer's report.
You can find a conclusion and name what an argument is assuming. This unit is six particular things arguments do, and the first rule of all six is the same: each has a twin that is perfectly good reasoning, so the job is telling them apart rather than learning a name.
| Term | What it means |
|---|---|
| Relevant expertise | Knowledge or experience suited to the exact question being considered. |
| Expert testimony | A specialist's statement offered as evidence within the relevant area of competence. |
| Independent source | A source with a separate evidential basis, rather than another repetition of the same claim. |
| Scope | The conditions and limits within which a statement is being made. |
Read the three things said about the footbridge, and notice that the parish cannot avoid deciding. Shutting a sound bridge costs everyone on the far side a mile each way, every day, for months. Leaving a cracked one open costs something nobody wants to name.
All three speakers are quoted as though their word settled it, and all three are believed by somebody in the room. So the question in front of you is not which of them is nicest or which of them is best known. It is which of these three quotations is evidence about cracked beams, and which are quotations about something else.
One of the three is easy once it is put that way. Two of them are not, and the reasons they are hard are different reasons. Hold the case in mind through the rest of the lesson; you will come back to it at the end.
An appeal to authority uses a person's statement as evidence. It is stronger when the speaker has relevant competence and a suitable basis for this particular claim. A famous name, an unrelated qualification, or confidence alone supplies no such connection. Even relevant expert testimony remains evidence that can be limited or outweighed.
The practical questions are: what exactly is claimed, what competence bears on it, how was the relevant information obtained, and what limits did the speaker state? A direct inspection may be important for a damaged object; an expert can also responsibly interpret reliable measurements gathered by others.
Refusing all testimony would discard much of what people learn from each other. Accepting every title without checking its relevance makes the opposite mistake. The aim is informed reliance: identify the connection between this speaker, this evidence, and this claim.
Another way: picture
Draw two circles: one is the subject the question belongs to, the other is the subject the person is trained in. When the circles sit on top of each other, quoting them is evidence. When they barely touch, the quotation is decoration, however large the second circle is.
Another way: steps
Three questions, in this order:
| What is offered | Why it is not evidence |
|---|---|
| Fame | Being known by many people is not knowing this subject |
| Confidence | Saying it firmly is not a reason for anybody to believe it |
| A qualification in something else | Expertise does not travel between subjects |
| Popularity of the person | Liking somebody is not evidence about what they said |
The third of those catches careful people out. A person with two degrees in chemistry really has been trained to be careful, and that training is about chemistry. Asked what a bus route costs, they are somebody with an opinion, like everybody else in the room.
One more, going the other way: experts in the right field do disagree, and when they do, quoting one of them settles less than it looks. That is a reason to ask what they disagree about, not a reason to throw all of them out.
An expert's title is a starting point for checking a claim, not a substitute for that check. Write the exact conclusion before deciding what expertise it requires. 'The beam has a crack', 'the crack reduces the bridge's load capacity', and 'closing the bridge is the best overall policy' are different claims. The first may be supported by a clear observation. The second needs relevant structural knowledge and information about the beam. The third also involves the consequences of different actions, available alternatives, and the community's priorities.
This distinction prevents expertise from silently expanding during an argument. An engineer may be well placed to assess the beam without being the sole authority on how school transport should be organized during repairs. A transport planner may estimate the diversion without being able to certify the beam. A good decision can combine both contributions. Asking whose knowledge bears on which claim is more useful than ranking the speakers as generally clever or generally untrustworthy.
Qualifications are one form of evidence about competence, but relevant experience can matter too. Someone who maintains a particular pump may know its maintenance history better than a researcher who has never seen it. A researcher may know general failure mechanisms better than the maintenance worker. Neither contribution must erase the other. Ask whether the claim concerns this device's history, a general technical relationship, or a recommendation that combines both. The relevant competence follows the question.
Next ask how the speaker obtained the information. Did they inspect the object, read a reliable report, analyze a suitable dataset, or merely repeat a rumor? Direct inspection is not always necessary: a climate researcher can assess a dataset collected by a monitoring network without visiting every station. Conversely, seeing an object does not automatically equip someone to interpret it. The important connection is a suitable route from evidence to this claim, not the literal requirement that every expert personally look at every case.
Then check the scope of the statement actually made. 'This repair usually lasts five years under these conditions' is not the same as 'your repair is guaranteed to last five years'. 'I found no visible crack in the inspected area' is not equivalent to 'no part of the structure has any defect'. A quotation can borrow genuine expertise and still overstate the expert's conclusion. Preserve qualifications, dates, and limits. If a report gives a range or a conditional forecast, do not turn it into an unconditional promise when summarizing it.
Finally separate evidence from entitlement to decide. A committee chair may have authority to sign a contract, while an engineer has expertise about a design. Institutional authority concerns permission or responsibility; epistemic authority concerns a reason to take a claim seriously. Someone may possess both, either, or neither in a particular situation. The chair's signature can establish that a decision was authorized without proving that the technical prediction behind it was correct.
Two qualified people can disagree without making expertise worthless. First ask whether they are answering the same question. One might discuss the beam's current condition while another discusses what will happen after repair. One might assume pedestrian use and another assume heavy vehicles. Apparent contradiction can disappear when the scope and assumptions are written side by side. If they really disagree, ask which evidence, method, or assumption produces the difference instead of selecting the more confident voice.
The number of quoted people is not automatically the number of independent sources. Five websites may all copy one interview. Three speakers may all rely on the same outdated inspection report. Count the underlying evidence paths, not merely the number of mouths or pages repeating a claim. Independent observations or analyses can add support; repetition of a single unsupported assertion does not become independent confirmation simply by traveling through several publications.
Conflicts of interest are another reason to examine a claim carefully, but they do not prove it false. A contractor who would be paid for a repair may still identify a genuine defect. The relevant response is to ask for the measurements, inspection criteria, and, where appropriate, an independent assessment. 'They stand to benefit, so their statement is false' replaces one unsupported inference with another. A possible incentive affects how testimony should be checked, not the truth value of the claim by itself.
Do not demand that a learner independently reproduce every specialist calculation before relying on an expert. That would defeat much of the value of expertise. A proportionate check might establish that the specialist has the relevant competence, used suitable evidence, stated the limits, and is not being quoted against a much stronger body of relevant work without explanation. The more consequential or surprising the claim, the more useful it becomes to look for the reasoning and context behind a brief quotation.
Equally, do not treat every disagreement as a balanced contest between equally supported positions. If one claim rests on a detailed current inspection and the other on a memory from twenty years ago, presenting them as two interchangeable opinions hides a material difference. Explain what each source contributes. The old memory may accurately describe the bridge's former condition while saying little about a recently discovered defect. A source can be reliable about one fact and insufficient for another.
When writing your judgment, use language that matches what you have established. 'This is relevant expert evidence about the beam' is often justified where 'the bridge is certainly safe' is not. 'The quoted sporting achievement does not support the road-design claim' is more precise than 'the speaker knows nothing'. A sound assessment identifies the question, the competence, the evidential basis, and the limits. It neither worships titles nor treats informed testimony as indistinguishable from a guess.
A fictional parish receives three statements about a footbridge used by 80 pedestrians on a weekday. A structural engineer reports that an inspected support beam has a crack whose significance requires a load assessment. A television presenter says the bridge looks beautiful and should remain open. A retired maintenance worker supplies records showing that the same beam was repaired eight years ago. The parish must distinguish contributions before deciding what further information it needs.
The engineer's competence is relevant to interpreting structural measurements, and the recent inspection provides a route to this beam. The careful wording matters: the report calls for an assessment rather than offering an unconditional guarantee of either safety or failure. The presenter may accurately describe the bridge's appearance, but attractiveness does not establish its load capacity. The maintenance records are relevant historical evidence, although a repair eight years ago does not settle the present crack's significance.
Now suppose six local articles quote the presenter, while only one prints the engineer's report. Six repetitions are not six structural assessments. They trace back to the same statement about appearance. Likewise, the figure of 80 users matters to planning the consequences of closure, but it does not calculate the beam's strength. The committee needs different evidence for different parts of its decision.
A responsible summary therefore says: 'We have a current specialist observation requiring further assessment, a historical repair record, and a favorable opinion about appearance.' That summary does not itself prescribe a real bridge-management decision. It makes the reasoning transparent so the responsible people can obtain the relevant assessment and consider practical arrangements without confusing popularity, beauty, and structural evidence.
Refusing every quotation. Once somebody learns the name of this mistake they start rejecting arguments that rest on a dentist, a mechanic or a meteorologist. That is worse than the original error: it throws away nearly everything anybody knows.
Counting the qualification and not the question. A degree makes somebody an authority on one subject and on no others.
Treating an expert's word as the end of the matter. Their word is evidence, and evidence can be outweighed — by a second expert, by a measurement, or by their never having looked at this case.
State the first claim precisely.
The inspected gearbox has worn bearings.
The question concerns the condition of a particular mechanical component.
Identify relevant competence.
The speaker repairs gearboxes professionally.
That experience bears directly on recognizing this kind of wear.
Identify the evidence route.
The mechanic dismantled this gearbox and measured the bearings.
The statement is tied to suitable information about this case.
State the second claim separately.
The local bus route will lose money next year.
This prediction concerns demand, costs, and revenue rather than bearing wear.
Limit the relevance of the credential.
Gearbox competence supports the first claim, not the financial forecast by itself.
A person's relevant authority does not automatically extend to a different question.
Name the claim made by a footballer.
The far end of the pitch stays wet after rain.
This is an observation about a surface the player regularly uses.
Identify the relevant experience.
The player has trained on that pitch for five seasons.
Repeated direct observation can support a local claim without a formal qualification.
Separate a stronger technical claim.
A new drain of a specified diameter would solve the problem.
Designing drainage requires information and competence beyond observing puddles.
Separate an unrelated planning claim.
The proposed river road is the best transport route.
Sporting fame adds no special basis for that transport comparison.
Summarize the contribution accurately.
Relevant evidence about recurring wet ground; no automatic drainage-design or road-planning authority.
The same speaker can supply useful observations and unsupported judgments on different questions.
Identify the current structural observation.
An inspecting structural engineer reports a crack requiring assessment.
The competence and evidence route match the beam question.
Preserve the observation's limits.
Crack observed; overall load capacity not yet settled by the quotation.
A call for assessment is weaker than a completed safety conclusion.
Identify the historical record.
Maintenance records show a repair eight years ago.
A dated record supports the history of that beam rather than its present capacity.
Identify the unrelated opinion.
A presenter calls the bridge beautiful.
Appearance is a different property from structural capacity.
Check apparent corroboration.
Six articles repeat the same presenter's statement.
Repeated quotation does not supply six independent technical assessments.
State what the evidence actually supports.
A current crack observation and a past repair, with further assessment needed.
Keeping each source attached to its claim prevents an unsupported overall guarantee.
Identify the specialist's claim and evidence.
A river specialist models flooding using current survey data.
Relevant methods and data can support a conditional forecast.
Identify the resident's distinct contribution.
A chef remembers no flooding during twenty years living beside the lane.
The recollection is local historical evidence, not expertise in every future flood condition.
Limit the conclusion from that recollection.
Four arguments that quote somebody. Match each to whether quoting that person is a good reason here.
| Their word is evidence here | Their word is not evidence here | |
|---|---|---|
| The vet has examined the dog and says the leg is not broken, so it is not broken. | ||
| A singer everybody has heard of says this medicine works, so it works. | ||
| The electrician checked the wiring and says it is safe, so it is safe. | ||
| A champion swimmer says the new tax is a mistake, so it is a mistake. |
Source 1 is a mechanic who inspected a gearbox. Source 2 is an accountant who checked sales records. Source 3 is a singer giving an unsupported opinion about road design. Complete the source numbers.
Find relevant mechanical testimony.
Gearbox condition: source gear.
The mechanic's work directly concerns the component.
Find relevant financial testimony.
Recorded sales: source sales.
The accountant has examined the financial records.
Find the claim resting only on unrelated fame.
Unsupported road-design authority: source road.
Singing supplies no stated basis for the road-design conclusion.
*Tomas's dentist has examined the tooth and says it needs filling. So it needs filling.* Is quoting that person a good reason here?
Build only the support links justified by the stated competence and evidence. A mechanic inspected a gearbox and reported worn bearings. An accountant checked the operator's records and reported a loss. A famous actor praised the bus color. Join each relevant source to the claim its work supports; leave irrelevant sources unconnected.
This task has no paper form; do it on a device.
Four people quoted in four arguments. For each, say whether the question is inside their field, and then whether quoting them is a sound step.
| What they are trained in | Is the question inside that field? | Is quoting them a sound step? | |
|---|---|---|---|
| A pharmacist, asked whether two medicines can be taken together | medicines | ||
| A novelist, asked whether a vaccine works | writing novels | ||
| A mechanic, asked what the noise in the gearbox is | engines | ||
| An athlete, asked whether the bridge will take a truck | running |
A dispute about a painting rather than a building. Mark the one step that leans on somebody who is not an authority on the question asked.
This task has no paper form; do it on a device.
Lesson test: one question per skill, one attempt each, no hints. Your answers are checked when you submit.
Construct the justified support map. A paper conservator examined a document and identified modern fibres. An archivist verified a ledger showing the document was acquired in 1980. A television host calls it inspiring. Connect each evidential source to the particular claim it supports. Acquisition in 1980 alone does not establish when the paper was manufactured.
This task has no paper form; do it on a device.
You can say when quoting somebody is a good reason and when it is a famous name standing where a reason should be, and you can explain why refusing every quotation is a worse mistake than the one it avoids. Tell somebody why a chemistry teacher's word on a bus route is worth no more than anybody else's. Next: when something about the person really is relevant.
15. A local resident and a river specialist, step 3
No remembered flood in twenty years does not establish that the lane will never flood.
A finite observation period cannot by itself support an unrestricted future guarantee.