Detecting Reasoning Errors

When someone counts up two groups to get a total, always ask: could the same person or thing belong to both groups at once? If yes, the total might be too high — that is the Overlap Fallacy.

Prize/award overlap questions appear regularly across NSW Selective and OC papers — easy marks once you know to look for the hidden shared member.

The examiner checks whether you can spot that two prize categories are not necessarily filled by different people, meaning the speaker's arithmetic can collapse when there is overlap.

A rule awards prizes (or points, or titles) to members of Group A and separately to members of Group B. A speaker counts them as separate people to reach a total. One option identifies that the same person might qualify for both groups.

Ferdinand thinks knowing a city's name is enough to find its country — but his hidden assumption is that every city name is unique. Find the option that disproves exactly that assumption.

Unwarranted assumption questions appear across all difficulty levels of NSW Selective TS — they test whether you can identify the gap between what someone says and what they quietly assume to be true.

The examiner checks whether you can extract a speaker's hidden assumption and match it to the option that directly invalidates it — rather than choosing options that are merely related to the topic.

A speaker claims they can do something (look something up, identify something, predict something) without needing extra information. Their method secretly relies on an assumption (uniqueness, completeness, consistency). One option disproves that assumption; the others are off-topic.

The rule says taller adults 'tend to' have larger feet. Monaro uses this to claim his dad's shoe size 'must' be at least 10. Kevin says that's not right. Who spotted the flaw?

Questions testing whether students notice the difference between 'tends to/usually' and 'always/must' appear regularly in NSW Selective TS. Treating a probabilistic rule as a guarantee is one of the most common reasoning errors tested — it appears in health, science, sport, and everyday statistics contexts.

The examiner checks whether students can spot the key qualifying word ('tend to') in the rule and recognise that it prevents any 'must' conclusion. Monaro makes the error of converting a trend into a guarantee. Kevin correctly notes that an exception is possible, which directly challenges Monaro's 'must.'

A rule uses soft language ('tends to', 'usually', 'generally', 'often'). One speaker draws a 'must' or definite conclusion from it. Another speaker correctly says the conclusion doesn't follow because exceptions are possible. Students must identify that the first speaker's error is treating a trend as a guarantee.

A school survey found that heavy bedtime readers slept fewer hours. John concludes reading stops you sleeping. But what if the sleepless students are reading to pass the time — not the other way around?

Reverse causation is one of the most common flawed-argument patterns on NSW Selective TS. Students see a correlation between two things and are shown a conclusion that picks the wrong causal direction. The correct answer always identifies that the cause and effect could be swapped.

The examiner tests whether students can (a) recognise that a correlation does not prove one specific causal direction, (b) see that poor sleep could cause more reading rather than more reading causing poor sleep, and (c) eliminate options that are irrelevant to John's logical mistake.

A survey or observation shows two things happen together (correlation). A person concludes that one causes the other. The correct answer points out that the causation could run in the opposite direction — the assumed effect is actually the cause.

Jake is going to the party; Robert is not. Natalie concludes Robert didn't do his homework. Daniel concludes Jake did. One of them has made a classic logic error — can you spot who?

'Whose reasoning is correct?' with a conditional rule is one of the most frequent question types on NSW Selective TS. One person always applies the contrapositive correctly (valid); the other always falls into the inverse or converse trap (invalid). Practising these patterns makes you fast at spotting which is which.

The examiner tests whether students can (a) recognise that Daniel correctly applies the contrapositive (going to the party → must have done homework), and (b) recognise that Natalie commits the inverse fallacy (not going → must not have done homework). The rule only flows one way: not done → can't go. 'Not going' does not prove 'not done'.

A conditional rule is given. Two people draw conclusions from observed facts (one uses the valid forward/contrapositive move; the other uses the invalid inverse or converse). Students must identify which person reasoned correctly.

To join the basketball team you must be 140 cm tall. Lauren grew to 141 cm. Miriam says she'll definitely be chosen. What's the mistake? The height rule is a necessary condition — it gets you through the door, but it doesn't guarantee you'll be chosen.

'Treating a necessary condition as sufficient' is one of the most tested flawed-argument patterns on NSW Selective TS. The rule establishes a threshold you must meet, but the person concludes that meeting the threshold alone is enough to guarantee the outcome.

The examiner tests whether students can (a) identify that the height rule is a necessary condition (must be 140+ to qualify) not a sufficient one (140+ doesn't guarantee selection), and (b) see that Option C directly names this gap (other factors might also be used), while Options A, B, D are irrelevant to Miriam's specific logical error.

A rule states a minimum requirement (height, age, score). A person meets the requirement and is told they will definitely succeed. The correct answer points out that the requirement is only one condition — other factors might also be needed.

Matt won five chess games last week. The overall record says each player wins 'around half.' Mr Stead concludes they must have played about ten games. The word 'around' is the hidden trap — he silently upgraded an approximation to an exact 50/50 split.

'Treating an approximation as exact' is a frequent and accessible error-detection pattern in NSW Selective TS. It typically appears with words like 'around,' 'about,' 'roughly,' or 'on average.' Students who don't notice the qualifying word often pick a distractor about unusual performance (Option A) rather than the precision error.

The examiner tests whether students can spot that 'around half' is not 'exactly half.' Mr Stead's calculation (5 wins × 2 = 10 games) only works if the split is exactly 50/50. Option B explicitly names this gap, while the other options introduce irrelevant ideas.

Someone uses a known approximation ('usually,' 'roughly,' 'around,' 'on average') and then makes a precise calculation that would only be valid if the approximation were an exact value. The question asks which option names or shows this mistake.

A common reasoning error is jumping from “two things happen together” to “one must be causing the other.” Your job is to name that mistake.

Correlation-versus-causation flaws appear often on Selective TS — in science, health, and everyday claims when a hidden third factor could explain both trends.

The examiner wants you to spot when evidence only shows association, not direction of cause — and when another explanation could produce the same pattern.

Someone observes X and Y occurring together and concludes X causes Y. Options offer alternative causes, irrelevant facts, or restatements of the claim.

Harder error-detection items give you a strict if-then rule and two speakers — you judge who follows the logic and who makes an illegal leap.

Two-character conditional questions recur in the harder band of Selective mocks: one person often uses the contrapositive correctly; the other confuses necessary with sufficient.

You must read the rule as an arrow (A → B), check valid forward inference, valid contrapositive (not-B → not-A), and reject affirming the consequent or assuming what the rule never states.

A school or certificate rule is quoted. Two students draw conclusions. You decide who is sound, who errs, or whether both are correct.

A single "whoever did X must have Y and Z" rule looks simple — but it generates exactly one valid family of conclusions. The rest are traps dressed as logic.

"Which sentence must also be true?" questions from a single conditional rule appear in the early-to-mid band of official NSW papers — they are high-value marks once you know the contrapositive shortcut.

The examiner tests whether you can separate the valid contrapositive (not-B → not-A) from the invalid converse (B → A) and the invalid inverse (not-A → not-B). Only one option survives the test.

A statement like "whoever committed X must have had both Y and Z" is given. Four options explore different logical directions from that rule — only the contrapositive of one of the necessary conditions must be true.

Two speakers make "if writing differs then reading differs" and "if reading is the same then writing is the same" — both look plausible, but the golden test is whether you can set up a simple equation to verify each claim.

"Whose reasoning is correct?" questions backed by a numerical scoring rule appear in the mid-band of official NSW papers — they reward students who translate the word problem into an equation before judging.

The examiner tests whether you can rearrange a sum equation (total = part A + part B) to reveal a constraint, then check whether each conditional claim follows from that constraint — and notice when two claims are secretly the same statement.

Two students scored equal totals made up of two components. Two characters each make a conditional claim about those components. You must verify which claims are valid using the equation.

When a rule says "you NEED X to do Y," having X does not guarantee Y — it only rules you out if X is missing. Will and Evie show exactly the difference between getting this right and getting it wrong.

Necessary vs sufficient condition questions appear regularly in NSW Selective TS — spotting the difference between 'required' and 'enough on its own' is one of the most tested logical skills.

The examiner tests whether you can apply a rule containing necessary conditions correctly: drawing conclusions only when a condition is absent (valid) rather than when all conditions are present (invalid).

A rule lists two or more requirements. Two people each apply the rule to a different person. One person correctly uses the contrapositive (missing condition → ruled out). The other assumes the conditions are sufficient and over-concludes. The question asks whose reasoning is correct.

Jack restates the rule directly. Amelia flips it around and negates both sides — that's the contrapositive, and it's always just as valid as the original. Both are right, and understanding why is one of the most powerful tools in logical reasoning.

Contrapositive questions — asking whose reasoning about a rule is correct — appear regularly in NSW Selective TS and are worth easy marks once you know the pattern: contrapositive = always valid, converse = not always valid.

The examiner tests whether students can recognise that the contrapositive of a rule is logically equivalent to the rule, and that applying a rule directly AND applying its contrapositive are both valid moves.

A box states a rule using 'only' or 'always'. Two people each draw a conclusion from the rule. One applies it directly; the other applies the contrapositive. Both are valid — the answer is 'Both' — but students must verify this rather than assuming one must be wrong.

The teacher promises Autumn spots to students who missed Spring — but says nothing about Spring performers. Jarrah wrongly assumes the rule works in reverse. That silent gap is where his mistake hides.

Inverse/converse error questions appear regularly across all difficulty levels of NSW Selective TS — they test the precise difference between what a rule guarantees and what it leaves open.

The examiner checks whether students can identify that a rule covering one group (those who missed Spring) makes no claim about another group (those who performed in Spring) — and that treating the silence as an exclusion is a logical error.

A rule promises something for Group A (missed the first event). A person in Group B (performed in the first event) assumes the rule also excludes them from the promise. The correct option points out that the rule is silent about Group B — silence is not the same as exclusion.

Six county records broken, ten qualifiers — Lisa says more than half must be record-breakers. But does 6 records always mean 6 students? Not if one student broke three records. One person, many events: that's the counting trap.

Double-counting / events-vs-people errors appear regularly in NSW Selective TS detecting-errors questions — they are especially tricky because the argument sounds logical until you notice it conflates a count of events with a count of people.

The examiner tests whether students can identify that the number of occurrences of an event does not necessarily equal the number of different people involved — a subtle but important distinction in counting arguments.

A character counts how many times something happened and incorrectly treats that count as the number of people involved. The correct option points out that the same person could have caused multiple occurrences, making the true people-count potentially much smaller.

Ms Walker splits her class by birthday to test whether milk improves times tables. The milk group scores higher — so milk works, right? Wrong. Children born in January are older than children born in December and may already be better at maths. The experiment was flawed before it started.

Flawed-experiment questions with confounding variables appear regularly in NSW Selective TS detecting-errors sets — they test whether students understand that a good experiment requires equally-matched groups before any treatment is applied.

The examiner tests whether students can identify that splitting groups in a non-random, biased way (birthday month = age = academic maturity) means any difference in results may come from the pre-existing difference, not the thing being tested.

A teacher or researcher runs an experiment by splitting a group in a convenient but biased way (birthday month, seat location, etc.), applies a treatment to one group, and then concludes the treatment caused a difference. The correct option points out the groups may not have been equal to begin with.

Ivy saw the waterfall a month ago but can't remember where she was. Annie says her brother's painting of the lookout view proves he was there more than two months ago. One of them is right — but the other is making a sneaky hidden assumption.

'Whose reasoning is correct?' questions with two speakers appear frequently in NSW Selective TS. Questions where one speaker reasons correctly and the other makes an unstated assumption are among the most common variations.

The examiner tests whether students can (a) apply a two-option elimination rule correctly, and (b) spot an unstated assumption — specifically the assumption that a painting must be created while physically present at the depicted location.

A short passage establishes two key facts (often about access or timing). Two speakers draw conclusions from those facts. One conclusion is logically airtight; the other contains a hidden assumption that may or may not be true.

113 red sentinels were spotted. Only 15 speckled greenbacks. Melissa concludes red sentinels are much more common. But what if one species is simply harder to see? Counting sightings is not the same as counting frogs.

Detection bias questions — where observational data is confused with true population or frequency data — appear regularly in NSW Selective TS under 'identifying mistakes in reasoning'. They are closely related to confounding-variable questions.

The examiner checks whether students can identify that observation count ≠ actual quantity, specifically when ease of detection differs between groups. Students must reject distractors that raise irrelevant issues (other locations, undiscovered species, seasonal effects) and home in on the core methodological flaw.

Two researchers count observations of two groups over time. One draws a population-level conclusion from the observation counts. Students must identify which option best describes the flaw — usually that one group is more visible, audible, or detectable than the other.

Three weather rules. One forecast. Victor thinks the indoor market proves it rained. Aidan thinks the beach proves the forecast was right. The difference? The beach has only ONE possible cause — the indoor market has two.

'Whose reasoning is correct?' questions involving conditional weather/scheduling rules with multiple possible outcomes are common in NSW Selective TS. Victor's error — ignoring a second condition that leads to the same outcome — is one of the most frequently tested reasoning mistakes.

The examiner checks whether students can track when an outcome has only ONE possible cause (making reverse-inference valid) vs MULTIPLE possible causes (making reverse-inference invalid). Victor ignores the 'might still go to the indoor market' clause in the overcast rule.

A set of if→then rules maps multiple conditions to various outcomes. Two speakers make reverse-inference claims ('if I see outcome X, condition Y must have happened'). One speaker's outcome has a single cause (valid); the other's outcome has multiple causes (invalid).

50 excursion places go to the first 50 students to hand in slips by Friday. Megan has already handed hers in. Kate is handing in on Friday. Both think the outcome is certain. Both are wrong — and for different reasons.

'Whose reasoning is correct?' questions where BOTH speakers are wrong are common in NSW Selective TS. They test whether students accept a conclusion too quickly just because it sounds plausible — here both Megan and Kate ignore one of the two conditions needed.

The examiner tests two distinct reasoning errors in a single question: (1) treating a necessary condition as sufficient (Megan assumes handing in = definitely getting a place), and (2) misreading a deadline as exclusive of the final day (Kate assumes Friday = too late).

Two conditions are required for an outcome. Two speakers each satisfy (or believe they satisfy) one condition and incorrectly conclude the outcome is certain or impossible. Students must evaluate whether each speaker has correctly accounted for ALL conditions.

Six groups, 15-point threshold, Fair Play Award — Lucy adds 12 + 14 + 1 = 27 finalist teams. But she’s making a classic counting mistake. Some of those teams qualify under MORE than one condition, and she’s counting them twice.

The overlap/double-counting fallacy is one of the most frequently tested reasoning errors in NSW Selective TS. It appears whenever a character adds counts from overlapping groups and treats the total as the number of unique items.

The examiner checks whether students can recognise that 'at least one of N conditions' means qualifying teams form a UNION of groups — teams satisfying multiple conditions must be counted only once. Lucy treats the groups as completely separate, overstating the true total.

An 'at least one of several conditions' qualification rule is given. A character counts qualifying items from each condition separately and adds them. Students must identify that the addition overcounts due to teams qualifying under multiple conditions, and that the true total is FEWER (not more) than the sum.

Glen and Hayden need to qualify for the Port Sunday Canoe Race. They came third in their heat, won last year but a member has since left. Glen says getting her back is their 'only chance' — but has he missed a route?

'Missed option' errors are a staple of NSW Selective TS reasoning questions. A speaker lists two blocked routes and treats them as exhaustive, ignoring a third route that is still open. These typically appear in qualification, eligibility, or access-rule scenarios with multiple pathways.

The examiner checks whether students can (a) map all three qualification routes from the rules, (b) recognise that the wild card route is available to any team that failed routes 1 and 2 — including Glen and Hayden — regardless of whether the former member returns, and (c) confirm Hayden's conditional claim is precisely correct: if she returns, Route 2 opens and the heat result becomes irrelevant.

A set of rules gives multiple ways to satisfy a condition (qualify, enter, win, etc.). Two speakers each respond to the situation. One speaker lists two blocked paths and incorrectly concludes there are no remaining options, forgetting a third path. The other speaker makes a focused, correct conditional statement. Students must verify each claim against all the rules.

Ticket inspectors on the Northern Intercity Railway have not caught a single person in five years. Linda says they're a waste of money. But is 'never catching anyone' a sign of failure — or success?

The deterrence-effect flaw is a recurring category in NSW Selective TS Detecting Reasoning Errors. Students are shown evidence that a system 'never does anything visible' and must recognise that the system may be WORKING precisely because it prevents the problem from arising.

The examiner tests whether students can (a) identify Linda's implicit assumption that the only value of inspectors is in catching people, (b) recognise that the deterrent value of the inspectors' presence is being ignored, and (c) distinguish this correct criticism from three distractors that are irrelevant or that actually support Linda's argument.

A safety or enforcement system (inspectors, cameras, guards, fines) has produced no visible results (no catches, no incidents). A speaker concludes the system is useless. Students must identify that the speaker has ignored the deterrence effect — the system may be preventing the problem, not just responding to it.

In Bolivistan, the national team playing always means flags in shop windows. Rob sees no flags and concludes the team isn't playing. Paul sees flags and concludes the team must have been playing. One of them is making a valid logical move — the other is reversing the rule.

Contrapositive vs. converse errors are among the most frequently tested conditional logic patterns in NSW Selective TS. The rule goes one way (playing → flags); the contrapositive (no flags → not playing) is always valid; but the converse (flags → playing) is a common trap that appears in about 1–2 questions per NSW practice paper.

The examiner tests whether students can distinguish between (a) the contrapositive — Rob's valid move: no flags → not playing — and (b) the converse — Paul's error: flags → playing. The key insight is that flags might appear for reasons OTHER than the football team playing, so seeing flags is not sufficient proof the team was playing.

A rule establishes a guarantee in one direction (if P, always Q). Two speakers each use the rule. One speaker sees the ABSENCE of Q and correctly concludes not-P (contrapositive). The other speaker sees Q and wrongly concludes P (converse fallacy). The rule says nothing about whether Q can occur without P.

Four rules about roller-blading, roller-skating and ice-skating. Wei says Shane's years of ice-skating mean he can roller-skate. Talia says Hannah can't roller-blade so she can't roller-skate either. One of them chains the rules correctly — and Rule 3 is the key to catching the other's mistake.

Multi-rule 'whose reasoning is correct?' questions with four rules are among the trickiest versions on NSW Selective TS. They require chaining two rules forward (for the valid reasoner) AND using an explicit counter-example rule to expose the invalid reasoner's inverse fallacy.

The examiner tests whether students can (a) chain Rules 4 and 1 to validate Wei (ice-skate → roller-blade → roller-skate), (b) recognise that Talia's move (NOT roller-blade → NOT roller-skate) is the inverse of Rule 1, and (c) use Rule 3 as an explicit counter-example that confirms the inverse is invalid.

Four if-then rules about overlapping skills or categories are given. Two people draw conclusions — one chains two valid moves; the other uses an inverse or converse. One rule (like Rule 3 here) is placed specifically to confirm the invalid direction, helping students who know what to look for.

A school excursion is cancelled if fewer than 20 students sign up, OR if there aren't enough teachers (1 per 10 students). Rohan thinks 2 teachers guarantees the excursion goes ahead. Megan thinks cancellation always means too few students. Both are wrong — each forgot about the other reason.

'Two independent cancellation conditions' is a common structure in NSW Selective TS 'whose reasoning is correct?' questions. One person ignores the student condition; the other ignores the teacher condition. The key skill is finding a counter-example for each claim that exposes the overlooked condition.

The examiner tests whether students can (a) identify BOTH cancellation conditions (< 20 students OR insufficient teachers), (b) build a counter-example for Rohan (25 students + 2 teachers → cancelled despite 2 teachers available), and (c) build a counter-example for Megan (25 students + 2 teachers → cancelled due to teachers, not student numbers).

A policy has two separate conditions that must both be met. Two people each claim something about the outcome, but each person only considered one condition and ignored the other. Neither reasoning is correct. The correct answer is always 'neither'.

Birds often abandon disturbed nests. Lorenzo's dad disturbed a nest — so Lorenzo says there's a 'good chance it may be abandoned.' Katarina sees an abandoned nest and says it 'must have been disturbed.' One uses the rule correctly with a hedged claim; the other reverses the logic and uses 'must.'

'Often flows forward, not backward' is a classic NSW Selective TS pattern. Students frequently choose 'both' because both speakers seem to be using the same information. The key distinction is: (1) is the direction forward (cause → probable effect) or backward (effect → definite cause)? (2) is the word 'must' justified when the rule only says 'often'?

The examiner tests whether students can (a) identify that 'often' means probabilistic, not certain; (b) recognise Lorenzo's claim as a correctly hedged forward inference; (c) spot that Katarina reverses the conditional (abandoned → must have been disturbed) even though the stem says only 'disturbed → often abandoned'; and (d) note that nests can be abandoned for reasons other than disturbance.

A stem states a conditional with a qualifier ('often', 'sometimes', 'usually'). Two people reason about it: one applies it correctly in the forward direction with appropriate hedging; the other reverses it and uses a strong word ('must', 'definitely', 'can't have'). The correct answer is 'one person only.'

Tim beat Leon in Heat 1. Chloe says: if Leon qualifies, Tim will too. But every participant runs TWO heats. Leon's qualifying route might have nothing to do with Heat 1. Chloe ignores Leon's second heat entirely — and that's the mistake.

'Ignoring an alternative path to the same outcome' is a NSW Selective TS error-detection pattern that frequently appears in competition or tournament contexts. The key diagnostic is whether the stem gives each participant multiple independent chances to achieve the result.

The examiner tests whether students recognise that (a) each participant runs two heats and needs top 2 in only one; (b) Chloe's logic only holds if Leon qualifies through Heat 1; (c) Leon can qualify through his second heat, bypassing the Heat 1 comparison entirely; and (d) options A, B, D all miss this core structural flaw.

A system has multiple independent routes to a single outcome. Someone reasons that because person X performed better than person Y in route 1, X will also succeed if Y does. The mistake is ignoring that Y might succeed via route 2, making the comparison on route 1 irrelevant.

A flashing red light warns that the processor is starting to overheat. Yifan concludes no flashing means everything is fine. Ria concludes a continuous light means it has overheated. Both are wrong — the rule only defines what the flashing signal means, and nothing else.

Conditional-signal questions appear regularly in NSW Selective TS at medium and difficult levels — especially in the 'whose reasoning is correct?' format where both people misinterpret the same rule.

The examiner tests whether students can identify that a rule about one specific signal (flashing) says nothing about other states (not flashing, or on continuously). Both speakers draw conclusions the rule does not support.

A rule states what one specific signal means. Two people draw conclusions about different states — one about the absence of the signal, one about a completely different signal state. The correct answer is 'neither', because the rule covers only the one stated signal.

Two lizard species, one key difference: Indoras never eat ants. Keira says termites are useless as a test. Jun says ants are the only way you COULD know for certain. The word 'could' makes all the difference — and both turn out to be right.

'Whose reasoning is correct?' questions with two-speaker format appear regularly in NSW Selective TS — they often contain a subtle word ('could', 'might', 'always') that determines whether a statement is correct or overstated.

The examiner tests whether students can (a) build a comparison table from factual clues, (b) evaluate each speaker's claim against the table, and (c) pay careful attention to modal words like 'could' (possibility) vs 'will' (guarantee) that change the logical force of a claim.

Two species (or groups) are described with overlapping and exclusive dietary/behavioural traits. Two speakers make claims about what test would identify the species. Students must check which tests are conclusive and evaluate whether each claim is correct, paying attention to modal language.

Three ways to cross the Korra River, each with its own schedule and rules. Amanda thinks three consecutive ferry days means both bridges are broken. Declan thinks he can only ever cross on Sundays. Both are making absolute claims — and both can be shown wrong with one counterexample.

'Neither speaker is correct' answers are among the most challenging variants of 'whose reasoning is correct?' questions in NSW Selective TS. They appear when BOTH speakers make overly strong claims ('must', 'only ever') that each has a specific exception.

The examiner tests whether students can (a) build a full schedule table from the crossing rules, (b) find a specific counterexample to Amanda's claim (Sat-Sun-Mon requires only Archer damaged), and (c) notice that Declan's 'only ever on Sundays' fails because the ferry also runs on non-Sunday days when bridges are damaged.

A set of scheduling rules governs who can use which crossings on which days. An exception clause ('only if the bridge... is damaged') is deliberately placed to invalidate absolute claims. Two speakers each make an 'always/must/only ever' claim. Students must build a table and find counterexamples to both.

Three languages share some words, but animal words are always different between Kaiana and Sekludi. Patricia claims that a shared Mekani–Kaiana word can't be an animal. Yilin claims that a shared Mekani–Sekludi word can't be an animal. One of them is right — but which one, and why?

Language rule questions with 'whose reasoning is correct?' are a premium variant of conditional logic in NSW Selective TS. They require applying two-rule chains carefully, and the hardest type asks students to find why one speaker's chain doesn't reach the conclusion — often because the chain bypasses a key language.

The examiner tests whether students can (a) label the three languages and write rules as if-then statements, (b) trace Patricia's two-step chain (M+K → also S by Rule 1 → now K+S → not animal by Rule 2), (c) recognise that Yilin's M+S path bypasses Kaiana so Rule 2 never fires, and (d) construct a counterexample (animal word same in M and S but different in K) to disprove Yilin.

A set of language or membership rules describes shared words between groups. One rule says 'if in A and B, then also in C.' Another rule says 'A and C never share X-type items.' Two speakers each make a conditional claim. One speaker's chain correctly triggers both rules; the other's chain skips a group and never reaches the blocking rule.

Scrub jays move their buried nuts when watched — but only if they've stolen before. Logan says this means they can predict who'll steal. Kimberley says movers must have been stolen from. Both are wrong, but in completely different ways.

'Neither person is correct' is the hardest variant of the 'whose reasoning is correct?' question type on NSW Selective TS. Both errors are subtle and different: one upgrades reactive behaviour to predictive ability; the other swaps the direction of theft (thief vs victim).

The examiner tests whether students can (a) distinguish reactive behaviour (moving nuts when watched) from predictive ability (knowing which bird will steal), catching Logan's error; and (b) distinguish 'previously stolen from others' (thief) from 'had its own nuts stolen' (victim), catching Kimberley's error.

A scientific discovery gives two conditional facts. Two people each draw a conclusion that oversteps the given information — one by inferring additional cognitive ability, one by reversing the direction of a relationship. Neither conclusion actually follows from the stated facts.

Players are dropped 'usually' for poor play and 'sometimes' for poor attendance. Katya plays well but is being dropped. Kylie says she must be missing training. Fiona says perfect attendance + better play would definitely save her. The word 'usually' is the trap for both.

'Non-exhaustive list' errors are among the trickiest 'whose reasoning is correct?' questions on NSW Selective TS. Both people appear to reason correctly — but they both treat 'usually' and 'sometimes' as 'only,' which is the shared hidden flaw. The answer is always 'neither' in these cases.

The examiner tests whether students notice that 'usually' and 'sometimes' signal a non-exhaustive list of drop reasons. Kylie uses elimination (not reason 1 → must be reason 2) that only works if the list is complete. Fiona uses a sufficiency claim (neither reason → definitely safe) that also only works if the list is complete.

A stem gives two reasons for an outcome, using 'usually' and 'sometimes' (or 'often' and 'occasionally'). Two people draw opposite-type conclusions from a specific case. Both conclusions rely on the list being exhaustive, but the qualifying words prove it isn't.