'follows logically' questions

[sunj289]

Logical Reasoning Problem Set 4, # 337

Hi, I am having a difficult time correctly answering questions that asks "the conclusion above follows logically if which one of the following is assumed."

I forgot if this is the same type of question as assumption questions, or if it is more of a conditional questions (must be true).

If someone could please walk me through in how I should attack this question, I would really appreciate the help:
Question 337: No chordates are tracheophytes, and all members of Pteropsida are tracheophytes. So no members of Pteropsida belong to the family Hominidae.

The conclusion above follows logically if which one of the following is assumed?

Thanks!

[Luke Haqq]

Let's try to break this apart:

No chordates are tracheophytes, = C ~T

(Note If C ~T, then the contrapositive is T ~C. In other words, you can never have C and T together)

and all members of Pteropsida are tracheophytes. P T

(Contrapositive: ~T ~P)

So no members of Pteropsida belong to the family Hominidae. = P ~H

(Contrapositive: H ~P)


In trying to get to the right answer, note that a new element--Hominidae (H)--is added, so you'll need that in the right answer choice, which helps us eliminate (C) and (E).

Answer (A) is the opposite of the answer we want; if all Hominadae were trachephytes, then the conclusion couldn't follow. And answer (D) doesn't tell us anything.

(B), however, helps us get to the conclusion. If all Hominidae are chordates, and no chordates are tracheophytes, then members of Peteropsida can't belong to the family Hominidae.

This is like an assumption question, in that the correct answer choice fills in a possible gap within the argument. PowerScore classifies this type as a "justify the conclusion" question. It might not be necessary for the argument to be true, but if the answer choice is right, on a justify the conclusion question, it is sufficient to get to the argument's conclusion.

Hope that helps!

[sunj289]

thanks for the explanation! I'm going back through the Lesson Four (justify the conclusion section) to review the lesson.

Could I ask for your help in one more of the justify the conclusion problem? It's the same problem set, number 335.

" Columnist: Almost anyone can be an expert, for there are no official guidelines determining what an expert must know. Anybody who manages to convince some people of his or her qualifications in an area- whatever those may be- is an expert"

I'm having a difficult time diagramming the structure.

Thank you

[Emily Haney-Caron]

Hi sunj289,

expert almost anyone
manages to convince people expert

This leads to:
manages to convince people expert almost anyone

Good luck with studying!

[Mi Kal]

Hi,

This question on anyone being an expert (2017 LR Bible, Page 337 #3) has as part of the explanation that the Conclusion is "Almost anyone can be an expert." However, what makes that the Conclusion? To me, it seemed like a stated fact. Telling me that "Almost anyone can be an expert." And that the Conclusion was that someone who convinces others that they qualify as an expert. This led me to choose answer D.

I was wondering if you can clarify.

Thanks.

Michael

[Francis O'Rourke]

Hi Michael,

We have two options for what the conclusion can be, so let's rearrange the information using premise and indicator word to see which way makes more sense

1. Because anyone can be an expert, you can be an expert by convincing other people
2. Because you only need to convince someone else, almost anyone can be an expert

The first example makes much less sense than the second. If I told you anyone could become an expert, would you likely think that all an expert did was convince people? Probably not. The first conclusion is so specific and out of left field that there is no way I can prove that that is a way to become an expert simply by telling you that it is easy to be an expert.

Similarly, which of the following makes a better argument:

• Because you can ride this roller coaster, you only need to be 4 feet tall to ride it.
• Because you only need to be 4 feet tall, you can ride this roller coaster.

The second example makes some sense. If I know that there is only one requirement and that that was an easy requirement, I can determine whether I am allowed to ride the roller coaster. On the other hand, if I were told that I was allowed to ride the roller coaster, how would I ever determine which rules there were for height? How would I conclude that you only needed to be 4 feet tall?

Looking for a conclusion is a process of determining which statement best follows from the other statements. You should not worry about which statement sounds more like a "stated fact" (unless you see clear indicator words) since often times arguments are trying to conclude an objective fact.

[Mi Kal]

Hi Francis,

Thanks for the explanation.

This is really sound advice.

Looking for a conclusion is a process of determining which statement best follows from the other statements. You should not worry about which statement sounds more like a "stated fact" (unless you see clear indicator words) since often times arguments are trying to conclude an objective fact.

However, both examples seem to be saying the same thing to me. It's kind of like when you have a sentence and you rearrange it by taking the second half of the sentence and make it the first half of the sentence instead. For example,

"The football game was a real defensive battle with the final score being 7 to 3."

or

"With the final score being 7 to 3, the football game was a real defensive battle."

Thanks for trying.

Michael

[Eric Ockert]

Hi Michael!

The big difference between your example and Francis' examples is that in your example only the order changed. In Francis' examples, the "because" is modifying two different clauses (so it's more than just a change of order, it's changing the logic of what's being said). So Francis' example has a different premise in each case, one of which makes sense, the other one doesn't.

So let's take the second sentence in the second example:

Because you only need to be 4 feet tall, you can ride this roller coaster.

If we rearranged the order, we could make the statement:

You can ride this roller coaster because you only need to be 4 feet tall.

Now, that is the same statement in both cases, just with different order. But if we instead had said:

Because you can ride the roller coaster, you only need to be 4 feet tall.

That would be a different statement. The key is the "because." It indicates what statement is being used as support.

Hope that clarifies a bit!

[Mi Kal]

Thanks Eric