LSAT 109 | Section 3 | Logical Reasoning: Q22

LR Question 22 Explanation

QUESTION TEXT: If relativity theory is correct, no object can travel forward in…

QUESTION TYPE: Parallel Reasoning

CONCLUSION: If relativity theory is correct then either quantum mechanics’ prediction about tachyons is wrong or tachyons do not travel forward in time.

REASONING: Relativity theory says that nothing can travel forward in time faster than the speed of light. But quantum mechanics predicts that tachyons travel in time faster than the speed of light.

ANALYSIS: This is a good argument. If relativity is correct then tachyons cannot travel forward in time faster than the speed of light. So either they travel backwards or they don’t travel faster than the speed of light (i.e. the prediction was wrong, in one of two ways.)

The structure is: If A is true then either B is wrong or B is only true in a counterintuitive sense that doesn’t contradict A.

___________

1. This is just a description of a magazine article. It isn’t really a conclusive argument because it hasn’t examined whether there is other evidence in favor of the theory that English is descended from Proto-Indo-European. 
2. This is a bad argument. It shows that the defendant had either of the two necessary conditions for being guilty. But they aren’t sufficient conditions for showing his guilt.
3. CORRECT. If A is true (modern medicine) then either B is wrong (the witness is mistaken) or B is only true in a counterintuitive sense that doesn’t contradict A (the shaman was underground but his brain had oxygen.) 
4. This isn’t a good argument, because it hasn’t examined the strength of the evidence that shows Alexander might have been buried in Alexandria instead.
5. This isn’t a good argument, because it hasn’t shown whether big bang theory is in fact correct.