LSAT 155 - Section 1 - Question 13

This is a Flaw/Descriptive Weakening question.

The stimulus starts with a claim from many prominent physicists. So that’s OPP. They claim that energy is merely a theoretical construct. Next, the author gives a premise, that the theory of relativity tells us that there is no essential distinction between energy and mass, and draws an intermediate conclusion, that mass must also be a theoretical construct.

First, note that the author uses OPP to further her own argument. This is uncommon. Usually, when OPP is present, the author challenges it.

Next, let’s examine the reasoning in this sub-argument before moving on to the main argument. How strong is the support? Well, the two premises both rely on authority to establish the truth of their claims. The first premise relies upon the authority of “many prominent physicists.” The second premise relies upon the authority of the theory of relativity. When it comes to appeals to authority, the key question to ask is if the appeal is to relevant authority. If it isn’t, then that’s a flaw. Here, the appeals are to relevant authority. First to “many prominent physicists” on what energy is and second to the “theory of relativity” on the relationship between mass and energy. Does that mean the sub-conclusion is validly drawn? No. Arguments that rely on appeals to relevant authority are never valid. But they can be reasonable. This sub-conclusion, mass is a theoretical construct, is reasonable. We can weaken the argument and we can strengthen the argument.

The main argument proceeds to use this sub-conclusion as a major premise. It also supplies another major premise, that all physical objects are composed purely of mass and energy. From those two premises, the conclusion is drawn that physical objects must also be theoretical constructs.

Now let’s examine the reasoning in this main argument. Do you recognize the pattern? It’s a part-to-whole argument. One premise states that mass (and energy) has a certain characteristic (being a theoretical construct). Another premise states that physical objects (whole) are composed purely of mass and energy (parts). The conclusion attributes the characteristic of the parts to the whole.

This is what Correct Answer Choice (B) points out. It says that the argument overlooks the possibility that something (a physical object, the “whole”) may lack a feature (being a theoretical construct) even if it (a physical object) is composed purely of things (mass and energy, the “parts”) that have that feature (being a theoretical construct). That’s exactly right.

Answer Choice (A) says the argument fails to consider whether anything other than physical objects may be composed purely of mass and energy. That’s true, the argument didn’t consider this. Do mass and energy together make up other, non-physical object things? But, wait, it doesn’t matter. Whether the answer is yes or no has no bearing on why the argument is vulnerable to criticism.

Answer Choice (C) says the argument presumes without justification that two things may have different features even if there’s no essential distinction between them. But that’s descriptively inaccurate. The argument actually presumes the opposite. It presumes that two things (mass and energy) cannot have different features if there’s no essential distinction between them. That’s how it drew the intermediate conclusion that mass is also a theoretical construct.

Answer Choice (D) says that the argument fails to adequately address the possibility that features of some theoretical construct need not be shared by every theoretical construct. The argument didn’t address this but it didn’t need to. (D) thinks “theoretical construct” has a “feature,” but in the argument, “theoretical construct” is itself the “feature.” In the argument, “theoretical construct” is the feature of energy and it’s also the feature of mass. We can map (D)’s “theoretical features” onto “mass” and “energy” in the argument, but then we’d have nothing to map (D)’s “features” onto.

Answer Choice (E) says the argument presumes, without providing justification, that the fact that a suggestion has been made by a physicist proves the truth of that suggestion. This is the most attractive wrong answer. (E) targets the reasoning in the sub-argument. Specifically, (E) recognizes that the reasoning there relied on an appeal to authority. This is good. But where (E) missteps is in failing to recognize that the appeal is to (many) relevant authorities. (E) thinks the argument “presumes, without providing justification” that just because “a physicist” made a suggestion, the suggestion is true. But in reality, the argument “presumes, with justification” that because “many prominent physicists” made a suggestion, the suggestion is true. The former would be a glaring vulnerability. The latter, while not ironclad, is much less of a vulnerability. The former is not equivalent to the latter, and therefore (E) is descriptively inaccurate.