Series route: This guide belongs to the complete PSLE Learner’s Guide volume directory. The original PSLE Learning Guide supplies the wider English, Mathematics and Science route, while PSLE Science provide verified subject-specific continuation.
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This volume solves one precise learner problem: the learner says boiled seeds “do not respire” without explaining why they form a useful control, changes several conditions at once, or treats any colour or temperature difference as proof while overlooking microorganisms, unequal mass, moisture, insulation and indicator behaviour. The goal is durable control, not a remembered slogan. A Primary 6 learner should be able to identify the trigger, explain the mechanism, perform the decision under time pressure and reject an attractive answer that exceeds the evidence.
- Start with the exact mistake and the evidence boundary.
- Build the mechanism before memorising a shortcut.
- Study worked contrasts and name why the near-miss fails.
- Repair misconceptions with one targeted check each.
- Attempt graded independent practice before reading the explanations.
- Return after a delay and prove that the method transfers.
- Use the parent and tutor notes after the learner has attempted the work.
The problem beneath the mistake
A respiration investigation may compare living germinating seeds with boiled seeds. Boiling kills the seed tissues, so the boiled group is intended to provide similar seed material without living seed respiration.
The comparison is useful only when other relevant conditions are matched: seed type, mass or number, moisture, container, air volume, indicator amount, starting temperature, insulation and observation time.
If only the living seeds produce a larger temperature rise under matched conditions, the evidence supports the explanation that respiration in living seeds releases energy, some of which warms the surroundings.
If a carbon-dioxide indicator changes differently, the evidence may support carbon dioxide production by living material. The answer must name what the indicator detects and avoid calling the colour itself “respiration”.
Boiled seeds do not make the entire apparatus sterile forever. Microorganisms can be present or enter, and dead organic material may support them. Good design reduces this alternative and interprets unexpected changes cautiously.
Boiling can change water content and structure. Equal numbers of living and boiled seeds may not have equal mass or surface conditions, so matching by the variable relevant to the investigation matters.
A control is not a group in which “nothing happens”. It is a comparison designed to remove or reduce one proposed cause while keeping other conditions as similar as practical.
The experiment does not prove that respiration is the only possible source of every change. It supports a causal explanation to the extent that alternatives are controlled and the measurement behaves as expected.
Safety and hygiene matter. Experimental seeds are not food, sealed containers should be handled as instructed, and adult or teacher procedures govern boiling and disposal.
The reliable routine is state the tested mechanism, identify the living and non-living groups, match conditions, define the measured response, predict the contrast, inspect alternatives and limit the conclusion.
Core decision: Boiled seeds serve as a non-living comparison because boiling destroys living seed activity. When living and boiled groups are otherwise matched, a repeatable difference in carbon-dioxide evidence, oxygen evidence or temperature can support respiration as the cause, subject to indicator limits and contamination controls.
Controlled investigation changes the presence of the proposed biological process while holding other relevant variables steady. Evidence becomes persuasive through comparison, measurement and alternative explanations—not through the label “control” alone.
Mechanism: why the rule works
1. Name the tested process
State that respiration in living seed cells releases energy and involves gas exchange appropriate to the setup.
The explanation must connect the biological process to the measured response.
Diagnostic check. What observable consequence is predicted?
2. Define the comparison
Use living germinating seeds and boiled non-living seeds of comparable material.
The boiled group removes living seed respiration while retaining a similar physical sample.
Diagnostic check. What proposed cause differs between groups?
3. Match sample amount
Control mass, number, seed type and developmental condition as appropriate.
More material can change heat capacity, gas volume and available organic matter.
Diagnostic check. Are the samples genuinely comparable?
4. Match environment
Keep container, air space, moisture, temperature, insulation, indicator and time the same.
Each unmatched condition offers another explanation for the outcome.
Diagnostic check. What differs besides living status?
5. Read the instrument
Know whether an indicator responds to carbon dioxide, oxygen, acidity or temperature.
A response is evidence for a measured condition, not the process itself.
Diagnostic check. What exactly does the instrument detect?
6. Control microorganisms
Use appropriate preparation and interpret changes in the boiled group cautiously.
Dead seeds can still carry or support microbes that respire.
Diagnostic check. Could another living organism produce the response?
7. Use repeated evidence
Compare repeats and the size and direction of change.
One irregular result may reflect measurement noise, leakage or preparation differences.
Diagnostic check. Is the pattern consistent across trials?
8. Limit the claim
Conclude that results support, rather than absolutely prove, respiration as the explanation under the tested conditions.
Causal language should match the strength of the control and measurement.
Diagnostic check. Which alternatives remain possible?
Worked examples: make the decision visible
Pause before each answer. State the controlling evidence in one line, then complete the operation. The explanations deliberately contrast a valid route with a plausible but invalid one, because transfer grows when the learner can say why a tempting route does not apply.
Worked example 1: Temperature rise
Task. Living germinating seeds warm by 3°C; matched boiled seeds warm by 0.2°C.
Reasoning. The larger repeatable rise in the living group is consistent with energy released during respiration.
Answer. The result supports respiration as a source of warming.
Independent check. Check starting temperatures, insulation, sample mass and repeats.
Contrast-and-transfer pass. Keep the governing principle from “Temperature rise”, but change one surface detail in the task: Living germinating seeds warm by 3°C; matched boiled seeds warm by 0.2°C. Before recalculating or rewriting, name which evidence remains controlling and which detail has changed. The original conclusion—The result supports respiration as a source of warming.—may remain valid only if the changed detail does not alter the trigger, relationship or scope. Use the independent check again rather than trusting visual similarity. This second pass trains selection: the learner must decide whether the same method still applies, adapt one step when a condition changes, and refuse the method when its trigger disappears.
Worked example 2: Indicator change
Task. Only the living-seed flask changes a carbon-dioxide indicator as predicted.
Reasoning. The indicator reports a carbon-dioxide-related condition, and living status is the intended difference.
Answer. The contrast supports carbon dioxide production by living seeds.
Independent check. Confirm equal indicator volume, airtightness and time.
Contrast-and-transfer pass. Keep the governing principle from “Indicator change”, but change one surface detail in the task: Only the living-seed flask changes a carbon-dioxide indicator as predicted. Before recalculating or rewriting, name which evidence remains controlling and which detail has changed. The original conclusion—The contrast supports carbon dioxide production by living seeds.—may remain valid only if the changed detail does not alter the trigger, relationship or scope. Use the independent check again rather than trusting visual similarity. This second pass trains selection: the learner must decide whether the same method still applies, adapt one step when a condition changes, and refuse the method when its trigger disappears.
Worked example 3: Both groups change
Task. Living and boiled groups both show indicator change.
Reasoning. The control has not remained quiet; contamination, indicator drift or trapped gases may be involved.
Answer. Do not claim a clean causal contrast.
Independent check. Repeat with improved preparation and an apparatus-only control.
Contrast-and-transfer pass. Keep the governing principle from “Both groups change”, but change one surface detail in the task: Living and boiled groups both show indicator change. Before recalculating or rewriting, name which evidence remains controlling and which detail has changed. The original conclusion—Do not claim a clean causal contrast.—may remain valid only if the changed detail does not alter the trigger, relationship or scope. Use the independent check again rather than trusting visual similarity. This second pass trains selection: the learner must decide whether the same method still applies, adapt one step when a condition changes, and refuse the method when its trigger disappears.
Worked example 4: Unequal mass
Task. Twenty grams of living seeds are compared with five grams of boiled seeds.
Reasoning. Sample amount differs as well as living status.
Answer. The comparison is confounded.
Independent check. Match mass before interpreting response size.
Contrast-and-transfer pass. Keep the governing principle from “Unequal mass”, but change one surface detail in the task: Twenty grams of living seeds are compared with five grams of boiled seeds. Before recalculating or rewriting, name which evidence remains controlling and which detail has changed. The original conclusion—The comparison is confounded.—may remain valid only if the changed detail does not alter the trigger, relationship or scope. Use the independent check again rather than trusting visual similarity. This second pass trains selection: the learner must decide whether the same method still applies, adapt one step when a condition changes, and refuse the method when its trigger disappears.
Worked example 5: Unequal temperature
Task. Living seeds begin warm after soaking while boiled seeds begin cool.
Reasoning. Starting temperature can explain part of the difference.
Answer. Equilibrate both groups before measurement.
Independent check. Record time-zero values.
Contrast-and-transfer pass. Keep the governing principle from “Unequal temperature”, but change one surface detail in the task: Living seeds begin warm after soaking while boiled seeds begin cool. Before recalculating or rewriting, name which evidence remains controlling and which detail has changed. The original conclusion—Equilibrate both groups before measurement.—may remain valid only if the changed detail does not alter the trigger, relationship or scope. Use the independent check again rather than trusting visual similarity. This second pass trains selection: the learner must decide whether the same method still applies, adapt one step when a condition changes, and refuse the method when its trigger disappears.
Worked example 6: Waterlogged group
Task. Boiled seeds are submerged while living seeds are damp.
Reasoning. Air availability and moisture differ.
Answer. The control is not matched.
Independent check. Use equivalent moisture conditions appropriate to the design.
Contrast-and-transfer pass. Keep the governing principle from “Waterlogged group”, but change one surface detail in the task: Boiled seeds are submerged while living seeds are damp. Before recalculating or rewriting, name which evidence remains controlling and which detail has changed. The original conclusion—The control is not matched.—may remain valid only if the changed detail does not alter the trigger, relationship or scope. Use the independent check again rather than trusting visual similarity. This second pass trains selection: the learner must decide whether the same method still applies, adapt one step when a condition changes, and refuse the method when its trigger disappears.
Worked example 7: No change
Task. Neither group changes during a short trial.
Reasoning. The process may be too slow, seeds may be inactive, apparatus may leak or measurement may lack sensitivity.
Answer. Absence of measured change is not automatic proof of no respiration.
Independent check. Check viability, duration and apparatus response.
Contrast-and-transfer pass. Keep the governing principle from “No change”, but change one surface detail in the task: Neither group changes during a short trial. Before recalculating or rewriting, name which evidence remains controlling and which detail has changed. The original conclusion—Absence of measured change is not automatic proof of no respiration.—may remain valid only if the changed detail does not alter the trigger, relationship or scope. Use the independent check again rather than trusting visual similarity. This second pass trains selection: the learner must decide whether the same method still applies, adapt one step when a condition changes, and refuse the method when its trigger disappears.
Worked example 8: Apparatus blank
Task. An empty flask with indicator also changes.
Reasoning. The measurement system changes without seeds.
Answer. The indicator or environment needs investigation.
Independent check. A blank control exposes apparatus-level drift.
Contrast-and-transfer pass. Keep the governing principle from “Apparatus blank”, but change one surface detail in the task: An empty flask with indicator also changes. Before recalculating or rewriting, name which evidence remains controlling and which detail has changed. The original conclusion—The indicator or environment needs investigation.—may remain valid only if the changed detail does not alter the trigger, relationship or scope. Use the independent check again rather than trusting visual similarity. This second pass trains selection: the learner must decide whether the same method still applies, adapt one step when a condition changes, and refuse the method when its trigger disappears.
Worked example 9: Unexpected warming
Task. Boiled seeds warm strongly after two days.
Reasoning. Microbial growth or another uncontrolled source may be acting.
Answer. Treat the boiled group as compromised until tested.
Independent check. Inspect hygiene, odour, moisture and repeats safely.
Contrast-and-transfer pass. Keep the governing principle from “Unexpected warming”, but change one surface detail in the task: Boiled seeds warm strongly after two days. Before recalculating or rewriting, name which evidence remains controlling and which detail has changed. The original conclusion—Treat the boiled group as compromised until tested.—may remain valid only if the changed detail does not alter the trigger, relationship or scope. Use the independent check again rather than trusting visual similarity. This second pass trains selection: the learner must decide whether the same method still applies, adapt one step when a condition changes, and refuse the method when its trigger disappears.
Worked example 10: Conclusion wording
Task. Write a conclusion from a matched, repeated temperature comparison.
Reasoning. Living seeds showed a greater temperature rise than boiled seeds under the same conditions, supporting the explanation that respiration released energy.
Answer. The wording links evidence, mechanism and boundary.
Independent check. It does not claim absolute proof or invent gas measurements.
Contrast-and-transfer pass. Keep the governing principle from “Conclusion wording”, but change one surface detail in the task: Write a conclusion from a matched, repeated temperature comparison. Before recalculating or rewriting, name which evidence remains controlling and which detail has changed. The original conclusion—The wording links evidence, mechanism and boundary.—may remain valid only if the changed detail does not alter the trigger, relationship or scope. Use the independent check again rather than trusting visual similarity. This second pass trains selection: the learner must decide whether the same method still applies, adapt one step when a condition changes, and refuse the method when its trigger disappears.
The method lab: change one condition at a time
Draw a variable table with changed variable, measured variable and controlled variables. Include seed status, temperature change and every matching condition.
Predict results for living seeds, boiled seeds and an apparatus-only blank. Explain what each comparison can and cannot rule out.
Audit three flawed designs: unequal mass, different indicator volumes and different starting temperatures. Repair only one variable at a time.
Interpret a data table containing one anomalous repeat. Calculate the pattern without deleting the anomaly silently, then propose a discriminating follow-up.
After a delay, write a conclusion using observation, comparison, mechanism and limitation in four separate clauses.
Common misconceptions and targeted repairs
Misconception 1: A control means nothing changes
What the learner may think. The learner expects a perfect zero response.
Why it fails. Controls can drift or reveal contamination and instrument effects.
Targeted repair. Interpret the actual control result.
Misconception 2: Boiled seeds are sterile forever
What the learner may think. The learner ignores microorganisms.
Why it fails. Dead material can carry or support living microbes.
Targeted repair. Consider preparation and a blank control.
Misconception 3: Equal number means equal sample
What the learner may think. The learner counts seeds despite size differences.
Why it fails. Mass and surface conditions may differ.
Targeted repair. Choose the comparison measure relevant to the mechanism.
Misconception 4: Indicator colour is respiration
What the learner may think. The learner confuses response with process.
Why it fails. The indicator detects a chemical condition associated with the setup.
Targeted repair. Name what is measured.
Misconception 5: Any difference proves causation
What the learner may think. The learner overlooks unmatched conditions.
Why it fails. A difference supports causation only when alternatives are controlled.
Targeted repair. Audit variables before concluding.
Misconception 6: No change means no respiration
What the learner may think. The learner treats instrument silence as biological absence.
Why it fails. Duration, sensitivity, leakage or inactivity may hide a process.
Targeted repair. Check the measurement chain.
Graded independent practice with explained answers
Attempt each item without looking ahead. Write the evidence or relationship before the final response. Early items check recognition; middle items require explanation; later items change the surface form so that copying a worked example is insufficient.
Practice 1: Purpose
Question. Why use boiled seeds?
Explained answer. To provide similar non-living seed material without living seed respiration.
Why this earns trust. The proposed biological process is removed.
Transfer variation. Close the answer, wait several minutes, and rebuild the reasoning with different names, values or wording while preserving the same decision. Start by stating the evidence that activates the method; then produce the response and a separate check. If the new surface detail changes the governing condition, explain why the earlier answer pattern must not be copied. The aim is not to repeat “To provide similar non-living seed material without living seed respiration.” from memory, but to recreate a justified answer from the new evidence.
Practice 2: Changed variable
Question. What intended variable differs?
Explained answer. Whether the seed material is living and respiring.
Why this earns trust. The comparison isolates living activity.
Transfer variation. Close the answer, wait several minutes, and rebuild the reasoning with different names, values or wording while preserving the same decision. Start by stating the evidence that activates the method; then produce the response and a separate check. If the new surface detail changes the governing condition, explain why the earlier answer pattern must not be copied. The aim is not to repeat “Whether the seed material is living and respiring.” from memory, but to recreate a justified answer from the new evidence.
Practice 3: Controls
Question. Name four matched conditions.
Explained answer. Sample mass, seed type, container, moisture, starting temperature, indicator amount and time are valid examples.
Why this earns trust. Each could affect the response.
Transfer variation. Close the answer, wait several minutes, and rebuild the reasoning with different names, values or wording while preserving the same decision. Start by stating the evidence that activates the method; then produce the response and a separate check. If the new surface detail changes the governing condition, explain why the earlier answer pattern must not be copied. The aim is not to repeat “Sample mass, seed type, container, moisture, starting temperature, indicator amount and time are valid examples.” from memory, but to recreate a justified answer from the new evidence.
Practice 4: Temperature
Question. Why might living seeds warm?
Explained answer. Respiration releases energy, some transferred as thermal energy.
Why this earns trust. Mechanism and observation are linked.
Transfer variation. Close the answer, wait several minutes, and rebuild the reasoning with different names, values or wording while preserving the same decision. Start by stating the evidence that activates the method; then produce the response and a separate check. If the new surface detail changes the governing condition, explain why the earlier answer pattern must not be copied. The aim is not to repeat “Respiration releases energy, some transferred as thermal energy.” from memory, but to recreate a justified answer from the new evidence.
Practice 5: Indicator
Question. What must an answer name?
Explained answer. The condition the indicator detects.
Why this earns trust. Colour is a measurement response, not the process.
Transfer variation. Close the answer, wait several minutes, and rebuild the reasoning with different names, values or wording while preserving the same decision. Start by stating the evidence that activates the method; then produce the response and a separate check. If the new surface detail changes the governing condition, explain why the earlier answer pattern must not be copied. The aim is not to repeat “The condition the indicator detects.” from memory, but to recreate a justified answer from the new evidence.
Practice 6: Contamination
Question. Why might boiled seeds still show change?
Explained answer. Microorganisms or apparatus drift may contribute.
Why this earns trust. The control result is interpreted, not ignored.
Transfer variation. Close the answer, wait several minutes, and rebuild the reasoning with different names, values or wording while preserving the same decision. Start by stating the evidence that activates the method; then produce the response and a separate check. If the new surface detail changes the governing condition, explain why the earlier answer pattern must not be copied. The aim is not to repeat “Microorganisms or apparatus drift may contribute.” from memory, but to recreate a justified answer from the new evidence.
Practice 7: Mass
Question. Why match mass?
Explained answer. Different amounts affect response size and physical properties.
Why this earns trust. Sample amount is a plausible alternative cause.
Transfer variation. Close the answer, wait several minutes, and rebuild the reasoning with different names, values or wording while preserving the same decision. Start by stating the evidence that activates the method; then produce the response and a separate check. If the new surface detail changes the governing condition, explain why the earlier answer pattern must not be copied. The aim is not to repeat “Different amounts affect response size and physical properties.” from memory, but to recreate a justified answer from the new evidence.
Practice 8: Blank
Question. What does an apparatus-only control test?
Explained answer. Change arising from the apparatus, indicator or environment without seeds.
Why this earns trust. It separates sample effects from system drift.
Transfer variation. Close the answer, wait several minutes, and rebuild the reasoning with different names, values or wording while preserving the same decision. Start by stating the evidence that activates the method; then produce the response and a separate check. If the new surface detail changes the governing condition, explain why the earlier answer pattern must not be copied. The aim is not to repeat “Change arising from the apparatus, indicator or environment without seeds.” from memory, but to recreate a justified answer from the new evidence.
Practice 9: No change
Question. Can one quiet trial prove no respiration?
Explained answer. No.
Why this earns trust. Sensitivity, duration and viability require checks.
Transfer variation. Close the answer, wait several minutes, and rebuild the reasoning with different names, values or wording while preserving the same decision. Start by stating the evidence that activates the method; then produce the response and a separate check. If the new surface detail changes the governing condition, explain why the earlier answer pattern must not be copied. The aim is not to repeat “No.” from memory, but to recreate a justified answer from the new evidence.
Practice 10: Repeat
Question. Why repeat trials?
Explained answer. To test consistency and identify irregular results.
Why this earns trust. Repeatability strengthens evidence.
Transfer variation. Close the answer, wait several minutes, and rebuild the reasoning with different names, values or wording while preserving the same decision. Start by stating the evidence that activates the method; then produce the response and a separate check. If the new surface detail changes the governing condition, explain why the earlier answer pattern must not be copied. The aim is not to repeat “To test consistency and identify irregular results.” from memory, but to recreate a justified answer from the new evidence.
Practice 11: Conclusion
Question. Use safe causal wording.
Explained answer. The contrast supports respiration as the explanation under the controlled conditions.
Why this earns trust. Claim strength matches evidence.
Transfer variation. Close the answer, wait several minutes, and rebuild the reasoning with different names, values or wording while preserving the same decision. Start by stating the evidence that activates the method; then produce the response and a separate check. If the new surface detail changes the governing condition, explain why the earlier answer pattern must not be copied. The aim is not to repeat “The contrast supports respiration as the explanation under the controlled conditions.” from memory, but to recreate a justified answer from the new evidence.
Practice 12: Routine
Question. State the sequence.
Explained answer. Mechanism, groups, matched conditions, measurement, prediction, alternatives, repeats and bounded conclusion.
Why this earns trust. The whole evidence chain is visible.
Transfer variation. Close the answer, wait several minutes, and rebuild the reasoning with different names, values or wording while preserving the same decision. Start by stating the evidence that activates the method; then produce the response and a separate check. If the new surface detail changes the governing condition, explain why the earlier answer pattern must not be copied. The aim is not to repeat “Mechanism, groups, matched conditions, measurement, prediction, alternatives, repeats and bounded conclusion.” from memory, but to recreate a justified answer from the new evidence.
A four-session mastery cycle
Session 1: construct. Read the mechanism once, cover it and write a three-line model containing the trigger, the operation and the check. Add one example and one near-miss. Compare only after the model is complete. If the operation is right but the trigger is missing, the knowledge is unsafe because it may be applied in the wrong place.
Session 2: discriminate. Mix six items: two that clearly require this method, two that tempt the method but violate a condition, and two that require another skill. For every item, write “use” or “do not use” before answering. Accuracy in method selection matters more than speed at this stage.
Session 3: explain. Give a complete answer to an imagined classmate. Include the smallest sufficient evidence, the mechanism and the independent check. Remove any sentence that merely repeats the question or adds an unsupported claim. A concise causal explanation is stronger than a longer collection of familiar words.
Session 4: perform. Attempt a timed mixed set without notes. Mark uncertain decisions, but continue. During review, classify each error as trigger, evidence, operation, scope, unit or check. Reattempt one changed version after a delay. Mastery is shown when the learner chooses and adapts the method without needing the original example beside it.
Delayed transfer: prove that the learning lasts
Transfer test 1: New instrument
Apply the design logic to a respirometer or gas indicator.
Success criterion. The measured variable is named accurately.
Transfer test 2: Flawed design
Repair one unmatched condition in an unfamiliar setup.
Success criterion. Only the confounding variable is changed.
Transfer test 3: Unexpected control
Explain a response in the boiled group.
Success criterion. At least two testable alternatives are proposed.
Transfer test 4: Delayed conclusion
Write a bounded conclusion from a new table after one week.
Success criterion. Evidence, mechanism and limitation remain separate.
Examination control
1. Name the target. State exactly what the question asks before selecting a rule or explanation.
2. Expose the relationship. Write the grammatical, numerical, causal or measurement relationship that controls the answer.
3. Use decisive evidence. Choose the smallest fact, calculation or observation that settles the decision.
4. Check the boundary. Reject the nearest tempting claim that the evidence does not support.
5. Present precisely. Keep conditions, units, certainty and scope visible in the final response.
Under time pressure, compress the method to mechanism → living/non-living groups → match conditions → read instrument → check microbes/repeats → bounded conclusion. The compressed routine is useful only after the full reasoning is understood. If it produces uncertainty, expand the step instead of guessing.
A compact error log
Use labels such as control purpose vague, sample unmatched, instrument misread, contamination ignored, no-change overclaimed or causation overstated.
Repeat the decision with a new apparatus diagram so the learner transfers experimental logic rather than memorising one seed setup.
Notes for parents and tutors
Focus discussion on fair comparison rather than recreating sealed biological experiments at home.
Ask what the indicator measures before asking what the result means.
Model safe uncertainty when a control behaves unexpectedly.
Follow school safety and hygiene procedures for seeds, boiling, containers and disposal.
Frequently asked questions
Why boil the seeds?
To kill seed tissues and remove living seed respiration from the comparison.
Are boiled seeds guaranteed sterile?
No. Microorganisms may still be present or enter.
What should be matched?
Sample amount, type, moisture, apparatus, temperature, indicator, air space and time.
Why can living seeds warm?
Respiration releases energy.
Does colour equal respiration?
No; it indicates a measured chemical condition.
Why use a blank?
To detect apparatus or indicator change without seeds.
Does no change prove no respiration?
No.
Best conclusion word?
“Supports” is usually safer than “proves”.
Next routes
Return to the complete volume directory to locate the series, use the original PSLE Learning Guide for the foundation route, and continue through PSLE Science for verified subject guidance. The next useful task is a mixed set in which this idea is sometimes relevant and sometimes irrelevant; that is where the learner must choose a method rather than imitate one.