Logical reasoning PrepTest 158 · Section 3 · Question 16

This answer choice brings up beliefs that are not grounded on observable evidence. To support this answer choice, we would need to use the second sentence from the passage. That sentence is a "some" statement, but this answer choice discusses all beliefs not grounded on observable evidence. That means the conclusion drawn by this answer choice is logically stronger than its support. Therefore, it is incorrect.

The second premise establishes that some beliefs based on reliable sources are not self-evident. Therefore, this answer choice must be false. How could all beliefs based on reliable sources be self-evident if some of those beliefs are not self-evident?

An experienced and decisive test-taker might read three words of this answer choice before eliminating it. The first premise in the passage establishes "reasonable beliefs" as a necessary condition. That is the only mention of reasonable beliefs in this passage. This answer choice attempts to put "reasonable beliefs" as a sufficient condition, which means this answer choice is committing the reverses-without-negating flaw. And, as discussed in the Answer Anticipation section above, we cannot conclude anything about "all reasonable beliefs." We can only make a conclusion about "some" reasonable beliefs.

This answer choice asserts a conditional relationship between a self-evident belief and a belief grounded on observable evidence. From the passage, we can only conclude that some beliefs based on a reliable source and some reasonable beliefs lack both conditions. That doesn't mean that there's a conditional relationship between the two — there could be many self-evident beliefs that are not based on observable evidence.

Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
If a belief is based on a reliable source, then it's reasonable to have that belief. Some beliefs based on reliable sources are neither self-evident nor based on observable evidence.

Strategy Overview:

1. Argument or facts in passage?
   1. If argument, identify premises and conclusions
2. Sufficient/necessary conditions in the passage?
   1. If so, diagram statements and draw any deductions
3. Use anticipation to find the answer choice that is absolutely 100% true

Answer Anticipation:
This set of facts features a conditional keyword ("If ... then") and a quantifier keyword ("some"), which is a strong signal we should diagram to help us draw a conclusion that must be true. For the "some" statement, recall that "neither this nor that" means "not this and not that." Our diagram should be:

1. Belief Based on Reliable Source → Reasonable Beliefs
2. Belief Based on Reliable Source -some- NOT Self-Evident & NO Observable Evidence

Remember the rules of combining a "some" statement and a conditional statement: (1) the term shared by the two statements must be the sufficient condition in the conditional statement; and (2) the conclusion must be a "some" statement containing the two non-shared terms. Because the first rule is satisfied, we validly could conclude:

Conclusion: Reasonable Beliefs -some- NOT Self-Evident & NO Observable Evidence

In un-diagrammed form, this would be, "Some beliefs are reasonable to maintain even though they're neither self-evident nor grounded in observable evidence." Further, since this is an "and" statement, the correct answer could mention only one of those conditions. For example, it could say, "Some beliefs are reasonable to maintain even though they're not self-evident." Or, "Some beliefs are reasonable to maintain even though they're not grounded in observable evidence." We should look for something similar to that in the answer choices.

Answer Choice Explanation:
In its incredibly wordy, difficult-to-parse way, this answer choice expresses the deduction we drew. Let's break it down, piece by piece. This answer choice refers to "reasonable beliefs," which is synonymous with "beliefs that are reasonable to maintain." The first part of this answer choice says, "Among reasonable beliefs that are not self-evident." This tells us these beliefs have two conditions: they're reasonable and NOT self-evident. If we were diagramming out this statement, we could write:

Reasonable Beliefs & NOT Self-Evident

Next, the answer choice tells us that some of these beliefs "are not grounded in observable evidence." If we were to add this to the above diagram, we would get:

Reasonable Beliefs & NOT Self-Evident -some- NO Observable Evidence

This doesn't quite look like the deduction we drew in the Answer Anticipation section, as that deduction had "NOT Self-Evident" on the right side of the "some" divider. However, with "some" statements, we can transpose conditions to either side of the arrow. After all, "some" just means at least one. From the passage, we can validly conclude that there's at least one belief that is (1) reasonable, and (2) not self-evident, and (3) not grounded on observable evidence. Both our initial deduction and this answer choice express that idea. (It would be equally valid to say, "Among beliefs that are not self-evident, there are some that are reasonable and not grounded in observable evidence.") So this answer choice must be true and is correct.

Key Takeaway:
Shrewd LSATers pay close attention to the strength of language of answer choices on Must Be True, especially those that involve "some" statements. Many incorrect answer choices attempt to draw conclusions that are stronger than the support the passage provides. In this case, each wrong answer choice could be eliminated because it attempts to draw an "all" conclusion from a "some" premise.