June 1998 LSAT Section 2 Question 20

Physicist: Determinism is the view that every event has a preceding cause sufficient for its occurrence. That is,...

Batman on November 16, 2014

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I have no idea why the answer is (d) and others are not answer. Isn't the answer of weakening question supposed to attack the premise or conclusion? Like your lessons, premise w/o conclusion, conclusions w/o premise, or alternative etc. Is (d) the answer because it proves premise without conclusion?? Thanks,

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Naz on November 25, 2014

This isn't a weaken question, it is an errors of reasoning question. Let's break down the argument.

The conclusion is that determinism is false.

Why? We know that determinism is the view that every event has a preceding cause sufficient for its occurrence. If determinism is true, then the events that are presently occurring could not have failed to occur given the state of the universe a moment ago, i.e. there is a complete state of the universe.

It is impossible to know the complete state of the universe at any given time since it is impossible to measure accurately both the position and velocity of any given subatomic particle at a particle time.

SO the reasoning follows:

P: determinism true ==> there is a complete state of the universe
there is not a complete state of the universe ==> determinism false

The issue with the argument is that the Physicist reasons because it is impossible to know the complete state of the universe at any given time, that means there is not a complete state of the universe. However, there is no information that states this in the passage; thus, we cannot infer it.

Just because we do not know what the complete state is, does not mean there is no complete state. Not knowing does not mean something does not exist, i.e. answer choice (D): "That it is impossible to know the complete state of the universe at any given time does not imply that there is no complete state of the universe at that time."

Hope that clears things up! Please let us know if you have any other questions.