Logical Reasoning · Inference (Cannot Be True)

PrepTest 124 · Section 2 · Question 2

Phase 1 (your first ~400 questions): read the guidance, then answer. No clock.

Step 1 · Pre-Question Guidance · read this first

Question type

Inference (Cannot Be True)

The one idea it tests

When the question asks which choices are possible EXCEPT one, hunt for the one choice the facts make impossible.

The basic logic

One person has two likes at once. A rule says nobody in a certain crowd has both of those likes together. A second rule gives the whole group a shared like. Chain them: since nobody in the group has both of the person's likes, nobody in the group can match the person's full set. Four choices are merely possible; one crashes into the rules.

Tiny words that decide it

“both”
“none”
“all”
“EXCEPT”

Playground logic

Kevin loves both kickball and tag, but none of his friends loves both. So no friend can love every game Kevin loves, because that would mean loving both. Everything else (friends liking hopscotch, liking one of the two, liking new games) is still possible.

Step 2 · The kid story

Kevin's Game Club

Kevin wanted a club for kids who love the same games he does. 'I love kickball AND tag,' he announced. Nadia raised her hand. 'Bad news. Every friend of yours picks one or the other. Nobody loves both.' Owen added, 'But we all love hopscotch. Every single one of us.' Marcus puffed out his chest. 'Then I bet one of us loves every game Kevin loves. Easy.' Lulu checked her clipboard. 'Kevin's games include kickball and tag. To love all of Kevin's games, you would have to love both. And nobody does.' Marcus tried again. 'Okay, but could one of us love tag and hopscotch?' 'Sure,' said Lulu. 'That breaks no rule.' Priya sipped her juice box. 'So lots of things could be true. Just not that one.'

Step 3 · Try the model question

Kevin loves both kickball and tag. None of Kevin's friends loves both kickball and tag. All of Kevin's friends love hopscotch.

If these statements are true, any of these choices might also be true, with one exception. Which one cannot be true?

Step 4 · The courtroom tale

The Case of the Double Badge

In Judge Okafor's courtroom, the scout troop's rulebook was read aloud. 'The troop leader holds both the knot badge and the map badge. No scout in the troop holds both.' A witness swore, 'One scout holds every badge the leader holds.' Mr. Whitfield stood. 'Your Honor, the leader's badges include knots and maps. Every badge the leader holds means both of those. The rulebook says no scout has both. So this claim cannot be true.' The witness blinked. 'Well, a scout could have the map badge and the campfire badge?' 'Absolutely,' said Mr. Whitfield. 'That one is fine.' The judge ruled the first claim impossible and left the rest alone.

Step 5 · Work the real question

Open PrepTest 124, Section 2, Question 2 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Write the rules as short arrows and notice the person who has two things the group never has together. Ask what any choice would require. For each choice, test whether it forces a group member to hold both. If it does, it is impossible and it is your answer. Choices that are merely surprising, new, or extreme but still allowed by the rules are possible, so leave them.