Logical Reasoning · Weaken

PrepTest 142 · Section 2 · Question 14

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

Step 1 · Pre-Question Guidance · read this first

Question type

Weaken

The one idea it tests

When an argument picks the 'other' explanation by ruling one out, show that the other explanation is ruled out too.

The basic logic

The argument says: it looks like A did it, but A could not have been around then, so B probably did it. To weaken, show that B could not have done it either, which leaves A (or something like it) back in play.

Tiny words that decide it

“probably”
“rather than”
“earlier than”

Playground logic

Marcus says the crumbs came from crackers, not candy, because they showed up before Tommy got any candy. The burger depends on crackers being able to make those crumbs then. Show that the right crackers were not there yet, and his cracker theory pops.

Step 2 · The kid story

The Backpack Crumbs

Lulu found tiny, sparkly crumbs in Tommy's backpack on Tuesday. They looked exactly like candy crumbs. But Tommy's first candy of the week was not bought until Thursday. Marcus pulled out his magnifying glass. "So the crumbs are probably from Tommy's crackers, not candy. Elementary!" Priya sipped her juice box. "Which crackers? The only crackers in the house that crumble into sparkly bits are the new cheese ones." Lulu checked the shopping receipt on her clipboard. "Bought Friday." Owen whistled. "So crackers couldn't have made those crumbs on Tuesday either." Marcus slowly lowered his magnifying glass. "Then maybe Tommy had candy earlier than we knew." Tommy, behind the couch, stopped chewing.

Step 3 · Try the model question

The crumbs in Tommy's backpack look like candy crumbs. But they appeared on Tuesday, and Tommy's first known candy this week was bought Thursday. So the crumbs probably came from crackers, not candy.

Suppose each choice below were true. Which would hurt Marcus's cracker theory the most?

Step 4 · The courtroom tale

The Midnight Doorbell

A homeowner claimed a prankster rang her doorbell at midnight. The defense said, "No prankster lived on the street until June, and the ring was in May. So it was probably a short circuit, not a person." Mr. Whitfield called an electrician. "In this house, the only wiring fault that could ring the bell was installed in August," she said. "In May, the wiring simply could not do it." The judge raised an eyebrow. "So your short circuit had not been born yet." The defense lawyer shuffled papers. Mr. Whitfield adjusted his suspenders and said nothing. Sometimes the best argument is a quiet one.

Step 5 · Work the real question

Open PrepTest 142, Section 2, Question 14 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Identify the two candidate explanations and the timing fact used to rule one out. Note the argument is quietly assuming its chosen explanation was possible at that time and place. Hunt for a choice that removes that possibility. Cross off choices that support the chosen explanation, that only question the dating in general, or that talk about how hard it is to find evidence without touching the chosen cause.