LSAT 102 | Section 2 | Logical Reasoning: Q20

LR Question 20 Explanation

QUESTION TEXT: Physicist: Determinism is the view that every event…

QUESTION TYPE: Flawed Reasoning

CONCLUSION: Determinism isn’t true.

REASONING: We can’t know if determinism is true.

ANALYSIS: This is a bad argument, but the error is common. I don’t know whether determinism is true. But it might be – there’s just no way for us to measure it.

Determinism means that every past moment in your life lead you to this moment, where you’re reading these words.

Don’t let the scientific language confuse you. Subatomic particle just means: really small thing. They’re only important because we can’t measure them fully. That means we can’t measure the full state of the universe. Therefore we can’t know whether determinism is true.

This is a reference to Heisenberg’s uncertainty theory. We can measure either the position or velocity of a particle, but not both.

___________

1. The physicist never said this. He just said we can’t know both position and velocity of a single particle. He didn’t say anything about measuring position or velocity separately for all particles.
2. This gets the physicist’s claim backwards. The physicist said that because we can’t fully measure subatomic particles, we can’t fully know the state of the universe.
3. This is very similar to A. Subatomic particles aren’t that relevant. In any case, the physicist never said anything about measuring position and velocity separately.
4. CORRECT. The universe might have a complete state, even if we can’t measure it. The physicist judged that determinism was false, but he had no evidence.
5. Actually, if we can’t measure both position and velocity for any particular particle, then we can’t do that for all particles. It’s a valid logical deduction. It’s like saying: “if any particular human can’t fly, then therefore all humans can’t fly.”

Recap: The question begins with “Physicist: Determinism is the view that every event”. It is a Flawed Reasoning question. Learn more about LSAT Flaw questions in our guide to LSAT Logical Reasoning question types.