#16 - If a belief is based on information from a reliable source, then it is reasonable

[Luke Haqq]

Complete Question Explanation

Must Be True. The correct answer choice is (E).

In this stimulus, we have two pieces of conditional reasoning. The first sentence, "If a belief is based on information from a reliable source, then it is reasonable to maintain that belief," can be diagrammed as:

Belief based on reliable source Reasonable

We're then told in the second sentence that "some beliefs are based on information from a reliable source and yet are neither self-evident nor grounded in observable evidence." This can be diagrammed as:

Belief based on reliable source Self-evident & Grounded in observable evidence

Since conditional reasoning using "some" is biconditional, we can connect these two statements together:

Self-evident & Grounded in observable evidence Belief based on reliable source Reasonable

Finally, when we have something in the generic form:

A some B C

We can infer from this that:

A some C

Using the chain we have, this means we can infer:

Self-evident & Grounded in observable evidence Reasonable

That is, some beliefs that are neither self evident nor grounded in observable evidence are reasonable.

Answer choice (A): We don't know this to be true. To the contrary, we know from the final diagram that there are some beliefs that aren't grounded in observable evidence but are nevertheless reasonable.

Answer choice (B): This is too strong but close. If the word "some" were inserted at the start of this option, that would make it correct. We know from the above conditional reasoning that some beliefs based on a reliable source are self-evident.

Answer choice (C): Mistaken Reversal. This is effectively saying, Reasonable Reliable, which is a reversal of the first diagrammed statement.

Answer choice (D): We don't know the connection between self-evident beliefs and beliefs not grounded in observable evidence. We have both of these on one side of the arrow, but not any conditional reasoning in which one implies something about the other.

Answer choice (E): This is the correct answer choice. The final diagram above tells us that there are some beliefs that are not self-evident and also not grounded in observable evidence but are still reasonable. That is equivalent to what (E) says: "Among reasonable beliefs that are not self-evident, there are some beliefs that are not grounded in observable evidence."

[gwlsathelp]

Question type: must be true, formal logic

Correct answer: E) "among reasonable beliefs that are not self-evident, there are some beliefs that are not grounded in observable evidence"

Breakdown (paraphrased the variables):
belief reliable source reasonable maintain belief
belief reliable source self-evident + observable evidence

I selected answer choice D) "if a belief is not grounded in observable evidence, then it is not self-evident either," which is incorrect because it is just the necessary condition of the last proposition and the stimulus doesn't discuss regular old beliefs. The correct answer is basically saying, "of the beliefs with reliable sources (which is some of the overall beliefs with reliable sources) that are NOT self-evident, there are some (some can include all) that are NOT grounded in observable evidence too."

Feel free to correct me if I'm wrong.

[Adam Tyson]

All correct, gwlsathelp! We know from the stimulus that there must be some reasonable beliefs (from reliable sources) that are neither self-evident nor based on observable evidence. That proves there is at least once reasonable belief that has both of those conditions. And yes, D was incorrect because those two conditions are neither sufficient nor necessary for each other. There could be some beliefs that are self-evident yet not grounded in observable evidence, as well as some that are not self-evident but are grounded in observable evidence.

[Katherinthesky]

Is (C) incorrect because it makes a conditional flaw (Mistaken Reversal)?

Thanks in advance.

[Robert Carroll]

Katherinthesky,

Yes, that's a Mistaken Reversal.

Robert Carroll

[DaishiMT]

Hi Adam,

Re: " We know from the stimulus that there must be some reasonable beliefs (from reliable sources) that are neither self-evident nor based on observable evidence. That proves there is at least once reasonable belief that has both of those conditions."

Can you kindly explain how is it the case that there is at least once reasonable belief that has both of the conditions? I'm confused on why there is an overlap of the two condition based on the neither nor condition. Thank you so much!

[Robert Carroll]

DaishiMT,

"Neither A nor B" means "notA and notB". Based on the second sentence, then, there are some beliefs with all three of these properties at the same time:

1. based on information from a reliable source

2. not self-evident

3. not grounded in observable evidence

But based on the first sentence, every belief with the first property (based on information from a reliable source) is reasonable to maintain. Therefore, the beliefs with the three properties above also have another property: they are reasonable to maintain.

Robert Carroll

[nivernova]

I drew two separate diagrams and combined them as below

~Grounded <-s-> Reasonable <-s-> ~ self-evident.

How can we make any inference from the two "some trains" like the one above?

[Robert Carroll]

nivernova,

That just demonstrates why it's not wise to break the "some" apart. Refer to Luke's diagram at the top of the page. The "some" statement in the last sentence is an entire statement, not the combination of several statements. Some beliefs with both the quality of being non-self-evident and the quality of being not grounded in observable evidence are based on information from a reliable source. Those beliefs have all of those qualities. Any belief with one of those qualities (based on information from a reliable source) also has another quality (reasonable to maintain). That's how we get the connection. There's no connection of "somes" here - there's only one "some" in the stimulus! We can infer separate "somes" from that, but that's not the original statement we started with, which already connects everything within it.

Robert Carroll

[Jefferson9921]

I'm having trouble understanding why C is incorrect. Is it because it's an improper reversal of the conditional chain? As in, it would be correct to say that *some* reasonable beliefs for which a person has no observable evidence are based on info from a reliable source, but you can't say that *all* are?

I don't usually diagram conditionals in LR, but maybe this was a question where it would've benefitted me.

Thanks!