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NSW SelectiveYear 7 entry

Deductive reasoning in Selective Thinking Skills

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Deductive reasoning means working out what must be true from the facts given. In Selective Thinking Skills, your child uses only the clues, reads each 'all' rule one way and rejects answers that only might be true.

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The full lesson is in the SelectiveReady app. A free account opens How and Why Authors Write; this lesson needs a paid plan.

Updated 16 October 2026 · Facts checked 12 October 2026

Thinking Like a Detective (lesson preview)

A short preview from the SelectiveReady lesson “Thinking Like a Detective”, on deductive reasoning for the NSW Selective test.

Published:

Read the video transcript

Let's start digging. So, our investigation is going to focus on our two persons of interest, Tom and Sarah. For each of them, we're going to apply our all rule and check every possible conclusion against that tough, must-be-true standard. Remember, no assumptions. Let's break down the deductions. Okay, first up, Tom. The clues say he is in the chess club, and the clues also say that all students in the chess club wear glasses. So does Tom have to wear glasses? Yes, it must be true. That's a solid, confirmed deduction. Now, what about Sarah? We know she wears glasses. Does that mean she must be in the chess club? Ah, hold on. This is that invalid reversal trap we talked about. Just because all chess club members wear glasses doesn't mean everyone who wears glasses is in the chess club. So could she be in the club? Maybe, but is it certain? Absolutely not. And case closed. See, by sticking to the code, we found the right answer.

Thinking Like a Detective is a full lesson in the SelectiveReady app. A free account opens one lesson, How and Why Authors Write; the other lessons need a paid plan1SelectiveReady · 13 October 2026 · Published. The preview plays here with captions in English and Chinese.

2

What will your child learn in this lesson?

Your child learns to think like a detective who solves the case from the evidence alone. They'll be able to follow the detective's code, use an all statement the right way round, and tell an answer that must be true from one that only might be.

The clip solves the case of Tom, Sarah and the chess club. The full lesson adds the code, the all rule, must versus might and three traps.

3

How does deduction show up in Selective Thinking Skills?

Your child reads a few short facts and is asked which conclusion must also be true. The facts are told as certain, even when they sound odd.

The Thinking Skills testWhat it means for deduction
critical thinking and problem solving, with no previous knowledge needed2NSW Education · 12 October 2026 · PublishedReal-life knowledge stays out; only the facts given count
42NSW Education · 12 October 2026 · Published options per questionTest each one with the question: must this be true?
23NSW Education · 12 October 2026 · Published sheets of working paperRoom to draw circles for all and some
The practice papers say there are no marks lost for incorrect answers4NSW Education · 13 October 2026 · PublishedChoose the option the facts force, then move on
4

What is deductive reasoning?

Deductive reasoning starts with facts you accept as true and works out what must follow. If all cats have tails and Tibby is a cat, Tibby must have a tail. The conclusion is certain because the facts are.

It's different from guessing a pattern from examples, which is called inductive reasoning.

Deductive reasoningInductive reasoning
Starts withRules or facts accepted as trueExamples you've seen
Ends withA conclusion that must be trueA pattern that's probably true
ExampleAll cats have tails. Tibby is a cat. So Tibby has a tail.Every swan I've seen is white, so swans are probably white.

Thinking Skills deduction questions ask for the first kind: what must be true.

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What is the method for deduction questions?

Follow the detective's code: use only the clues, no guessing, no outside knowledge. Then test every option against the strict standard of must.

Must or might? The chess club circle sits inside the wears-glasses circle. Tom: must wear glasses. Sarah: might be in the club.

  1. List the clues exactly

    Write each one down as given. If a clue says all dogs can fly, then in this puzzle dogs fly.

  2. Read all statements one way

    All A are B means every A is a B. It doesn't mean every B is an A.

  3. Combine the clues

    Put two clues together to find a new fact. Drawing a circle inside a circle helps.

  4. Ask must, not might

    For each option, ask whether there is any way it could be false. If there is, cross it out.

What do all, some and no mean in a clue?

These three words carry most deduction questions.

ClueWhat it tells youWhat it doesn't tell you
All A are BEvery A is also a BThat every B is an A
Some A are BAt least one A is a BWhether all of them are
No A are BA and B never overlap, so no B is an A eitherAnything about things that are neither
6

What does a worked deduction question look like?

We wrote this case to show the method.

Our practice case
All the players in the school orchestra can read music. Some Year 5 students play in the orchestra. Lina cannot read music.

Question: Which one of these must be true?

OptionStatement
ALina is not in the orchestra.
BAll Year 5 students can read music.
CEveryone who reads music is in the orchestra.
DLina is not in Year 5.
StepWhat your child does
List the cluesOrchestra players all read music. Some Year 5 students are players. Lina can't read music.
Use the all ruleEvery orchestra player reads music. Lina doesn't, so she can't be a player. A must be true.
Test BSome Year 5 students are players, not all of them. B might be true, but it isn't forced.
Test C and DC turns the all rule around. D might be true, but Lina could be in Year 5 and not play.
7

What mistake do children make with deduction?

The classic mistake is the reversal: reading all A are B as all B are A.

TrapWhat it looks likeThe fix
The reversalAll chess players wear glasses, so Sarah, who wears glasses, plays chessCheck which way the all rule runs
The might trapChoosing an answer that's possible, not certainAsk: could this be false?
The outside knowledge lureUsing real-world common sense the clues never gaveStick to the world the clues create
8

Can my child try one on their own?

Here is a question from our free Thinking Skills set. It combines an all clue with a some clue.

Practice question · SEL-TS-TST-07

Here are two facts about a school:

  • All the students in the art club are in Year 5 or Year 6.
  • Some students in the art club also play in the school band.

If these facts are true, which one of the following must also be true?

  1. A

    Some students in the school band are in Year 5 or Year 6.

  2. B

    All the students in the school band are in the art club.

  3. C

    No Year 4 students play in the school band.

  4. D

    Every Year 6 student at the school is in the art club.

Show answer and explanation

Answer: A

Answer: A (Some students in the school band are in Year 5 or Year 6.)

  1. Some art club students play in the band.
  2. Every art club student is in Year 5 or Year 6, so those band players are in Year 5 or Year 6.
  3. So at least some band members are in Year 5 or Year 6.

Why the other options are wrong

  • B: The facts say some art club students are in the band, not that every band member is in the art club.
  • C: The facts only describe art club students; band members outside the art club could be in any year.
  • D: The facts say every art club member is in Year 5 or 6, not that every Year 6 student joins the art club.

  1. List the clues

    Every art club student is in Year 5 or Year 6. Some art club students play in the band.

  2. Combine them

    Those band players are art club students, so they are in Year 5 or Year 6.

  3. Test the others

    B and D turn a clue around. C is about band players outside the art club, and the clues say nothing about them.

  4. Answer

    A. Some band members must be in Year 5 or Year 6.

9

How can my child practise deductive reasoning at home?

Deduction grows fastest through short talks, not pages of drills.

Must, might or can't?

Give two facts and a statement. Your child says whether it must be true, might be true or can't be true.

Silly-world clues

All dogs can fly. Rex is a dog. Practising with odd clues trains your child to leave real life out.

Draw the circles

For each all or some clue, draw circles inside or overlapping each other and read the answer off the picture.

10

Questions parents ask about deductive reasoning

What is an example of deductive reasoning for kids?

All birds have feathers. A robin is a bird. So a robin has feathers.

What is the difference between must be true and could be true?

Must be true is forced by the clues: it can't be false. Could be true fits the clues but isn't forced.

Does my child need general knowledge for deduction questions?

No. The Department says there's no new or special knowledge needed2NSW Education · 12 October 2026 · Published, and outside knowledge can lead your child astray.

Is the full lesson free?

A free account opens one lesson, How and Why Authors Write; the other lessons need a paid plan1SelectiveReady · 13 October 2026 · Published.

Next questions

Selective Thinking Skills →Lesson: If-Then Reasoning →Lesson: Solving Logic Puzzles →Lesson: Judging Arguments →Free Selective practice test →

Sources and checks

  1. SelectiveReady

    SelectiveReady · Checked 13 October 2026

  2. Selective high school practice tests

    NSW Department of Education · Checked 12 October 2026 · Practice materials: personal or non-commercial use only; CC BY 4.0 does not apply (page notice). Page text: CC BY 4.0.

  3. Placement test

    NSW Department of Education · Checked 12 October 2026 · CC BY 4.0 (NSW Department of Education copyright notice); quotes credited

  4. Selective High School Placement Test, Thinking Skills Question Paper, Practice Test 1 (2026 entry practice tests, PDF)

    NSW Department of Education · Checked 13 October 2026 · Practice materials: personal or non-commercial use only; CC BY 4.0 does not apply (page notice). Quoted briefly with credit. Saved text: the cover-page instructions only; the question pages are not stored (W§3.22).

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