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Logical Reasoning: Principles, Paradoxes and Explanations

Identifying and applying rules, plus LSAC's tenth ability: telling an explanation from an argument and resolving facts that only look like they collide.

8 topics · 34 questions

Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.

Principle: Identify

  1. How it worksHow does a principle sit above an argument as a broad rule the specific case slots into?
  2. Worked exampleWalk me through finding the principle behind 'Rita repaid the loan late, so she owes an apology'.
  3. Common mistakeWhy isn't the principle just the conclusion restated in slightly grander words?
  4. Going furtherWhat changes when a rule has to cover the case at hand without covering far too much else?
Your turneasy1 of 3
Rita borrowed 28 thousand from a neighbor and repaid it 40 days after the date she had undertaken to repay it. She therefore owes the neighbor an apology. The reasoning above conforms most closely to which one of the following principles?

Principle: Apply and Conform

  1. How it worksHow do you check a candidate case against every clause of a rule and not merely the first one?
  2. Worked exampleFind which case conforms to 'Keep a promise unless keeping it would cause serious harm'.
  3. Worked exampleWalk me through testing three candidate cases against 'Never criticize what you have not tried'.
  4. Common mistakeWhy doesn't a case that feels morally right conform to a rule whose terms never reach it?
Your turneasy1 of 3
Principle: A person should keep a promise unless keeping it would cause serious harm to someone. Several neighbors made promises 22 days ago, and each now has a reason to think again about the promise made. Which one of the following judgments most closely conforms to the principle above?

Principle: Strengthen and Justify

  1. How it worksHow must a justifying rule be wide enough to cover the case yet tight enough to force the verdict?
  2. Worked exampleFind the principle that most helps justify 'The museum should refund the ticket, since the exhibit was closed'.
  3. Common mistakeWhy isn't a rule that merely permits the conclusion as good as one that demands it?
  4. Going furtherWhat happens when the covering rule is so broad it sweeps in results nobody would accept?
Your turneasy1 of 3
Visitor: I paid 34 for a ticket to the museum's special exhibition, and when I arrived the exhibition was closed for repairs. The museum should refund my ticket. Which one of the following principles, if valid, most helps to justify the visitor's conclusion?

Principles versus Assumptions

  1. How it worksHow does a rule reach a whole class of cases where an assumption reaches only the case in front of you?
  2. Worked exampleWalk me through separating the rule from the assumption in 'Tom lied, so Tom should resign'.
  3. Common mistakeWhy doesn't every hole in an argument get plugged best by a broad rule?
Your turnmedium1 of 3
Tom told the committee that the 22 invoices had been paid, and they had not been. Tom should therefore resign his post. Which one of the following is an assumption about this case that the argument requires, rather than a general rule it relies on?

Paradox and the Apparent Discrepancy

  1. How it worksHow does a hidden third fact let both surprising facts stand with neither one being false?
  2. How it worksHow do you state the two colliding facts in one sentence before reading a single answer choice?
  3. Common mistakeWhy isn't the credited choice the one that denies one of the two given facts?
  4. Worked exampleWalk me through the puzzle in 'Speed limits fell yet the crash rate on that road went up'.
  5. Going furtherWhat changes when two facts really are contradictory and no resolution exists at all?
Your turneasy1 of 3
When the speed limit on the coast road was lowered from 104 to 63 kilometers an hour, the number of crashes on that road rose by 38 percent over the following year. Which one of the following, if true, most helps to explain the result described above?

What a Resolving Answer Must Do

  1. How it worksHow does the resolving fact draw as a bridge letting two colliding facts pass each other safely?
  2. Worked exampleFind what resolves 'Sales doubled while the store cut its advertising budget to zero'.
  3. Worked exampleWalk me through resolving 'The town hired lifeguards and drownings rose that same summer'.
  4. Common mistakeWhy doesn't a choice that explains only the surprising half resolve the discrepancy?
  5. Going furtherWhat happens when two choices both explain the puzzle and one of them explains more of it?
Your turneasy1 of 3
The Halcyon store cut its advertising budget to nothing in January, and over the following 8 months its sales ran 22 percent above the same months a year earlier. Which one of the following, if true, most helps to explain the store's sales figures?

Paradox EXCEPT

  1. How it worksHow does sorting choices into explains and fails-to-explain crack an EXCEPT paradox quickly?
  2. Worked exampleWalk me through a Paradox EXCEPT on 'Rain fell all week yet the reservoir level dropped'.
  3. Worked exampleFind the one choice that fails to explain 'The store raised prices and sold more units than ever'.
  4. Going furtherWhat changes when a choice explains the puzzle only under a fact the stimulus never granted?
  5. Common mistakeWhy doesn't a choice have to deepen the mystery in order to be credited on such a stem?
Your turnmedium1 of 3
Rain fell on the catchment every day for 6 weeks, yet the level of the reservoir it feeds dropped by 55 centimeters over that period. Each of the following, if true, helps to explain the drop EXCEPT:

Identifying Explanations

  1. How it worksHow does an explanation take a fact as settled where an argument is still trying to prove it?
  2. Worked exampleWalk me through deciding whether 'The engine stalled because the fuel line froze' argues or explains.
  3. Common mistakeWhy doesn't the word 'because' always mark evidence propping up a conclusion?
  4. Ties togetherHow does telling explanation from argument change which answers can weaken a stimulus at all?
Your turneasy1 of 3
Mechanic: The engine stalled on all 9 occasions because the fuel line froze. The line runs outside the housing, and every one of the stalls came on a morning colder than 18 degrees below zero. The mechanic's statements do which one of the following?

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