LR Question 24 Explanation
QUESTION TEXT: No mathematical proposition can be proven true by…
QUESTION TYPE: Sufficient Assumption
CONCLUSION: You can’t prove any mathematical theory true.
REASONING: You can’t prove any mathematical theory true by observation.
ANALYSIS: This argument is missing something. What if there are other ways to prove a mathematical theory true, apart from observation?
If we assume that there are no other ways to prove something true, then this is a good argument.
___________
- This doesn’t help. There still might be a way to prove mathematical theories true, apart from observation.
- This tells us that nothing can be proven true by observation. But it doesn’t tell us there are no other ways to prove a mathematical theory true.
- We need to know that if a proposition can’t be proven by observation then it can’t be proven true at all.
- This gives us a necessary condition. It says knowing is impossible “only if”. We need to know something is impossible “if:”.
It’s like if I say: “you can get there on time only if you drive”. That doesn’t mean you will get there on time if you drive, you might still be late. - CORRECT. Since we can’t prove math true by observation, this tells us we can never know if math is true.
Recap: The question begins with “No mathematical proposition can be proven true by”. It is a Sufficient Assumption question. Learn more about LSAT Sufficient questions in our guide to LSAT Logical Reasoning question types.
More Resources for Sufficient Assumption Questions
- Conditional Reasoning Article: Learn about conditional statements.
- LR Diagrams Guide: Learn how to draw LR diagrams.
- Intro to Conditional Reasoning: Learn conditional reasoning basics.
- Intro Course lesson: This intro course lesson covers Sufficient Assumption questions.
- Mastery Seminar lesson: This LR Mastery seminar lesson covers sufficient assumption questions.
We need: Not (Proven true by observation) –> Not (Known to be true).
Option a: Known to be true –> Proven true. This is because Proven true is the required condition. This is not what we need as ‘by observation’ is missing.
Option b: Mess.
Option c: Proven true by observation –> Known to be true. Not what we need.
Option d: Not (Known to be true) –> Not (Proven true by observation). Contrapositive of c.
Option e: Known to be true –> Proven true by observation. The contrapositive of this is what we need so this is the correct answer.