Q13 - Reptiles are air-breathing vertebrates

[b91302310]

I chose (A) and understood that why it is the correct answer. However, could anyone explain why answe (D) is incorrect?

Thanks

[ManhattanPrepLSAT1]

No problem, the issue with answer choice (D) is that it's a valid argument. The stimulus rests on an assumption, but answer choice (D) is a solid argument.

Diedre has seen every film by Fassbinder, and Ali: Fear Eats the Soul is a film by Fassbinder, then it follows that Diedre has seen Ali: Fear Eats the Soul.

Does that clear this up?

[soyeonjeon]

Would the logic of the stimulus be that
A ---> C
B ---> C (since we all know that B--> A)

For answer choice A, when it says Green plants .....
does that become a sufficient condition? Like "people who" is a sufficient condition, (without necessarily having "all"?)
What I'm saying is, for A, it doesn't say all green plants are..... and neither does the stimulus. But just saying "Reptiles are air-breathing vertebrates" or saying "green plants take in CO2 and..." Would those be conditional statements?

Thank you. Hope my question was understandable.

[sportsfan8491]

I personally refrained from diagramming this stimulus when I was doing it in timed practice, I just noticed that I was presented with a general claim about an entire group, and that claim was then extended to a "presumed" sub-group of the larger group. So I quickly jumped into the answers and saw (A) almost immediately. I obviously ruled out the remaining answers quickly before moving on.

To digress a bit, we're presented with a general claim about reptiles and then the passage extends this claim to a supposed sub-group (namely alligators), but makes a subtle assumption; it gets us to unknowingly make the common sense assumption that alligators actually belong to the larger reptile group and they exhibit the same characteristics as the larger group. The last time I checked, I'm pretty sure they were classified as reptiles in the real world. Nonetheless, I believe the argument is missing the "all alligators are reptiles and they exhibit all of the same characteristics as reptiles" conditional clause that would be needed in order to make this argument 100 percent valid from a symbolic logic perspective. Experts, please feel free to correct me, if what I've said is incorrect.

A) is correct because it presents us with a general claim about a particular group, green plants (which matches to the reptiles group in the stimulus), and then concludes that a sub-group, namely grass, exhibits the same exact characteristics as the larger group (the grass matches to the alligators from the stimulus). This answer, like the passage, makes the subtle assumption that "all grasses are green plants".

B) is wrong because it's a different form of invalid reasoning that takes a "some" statement to apply to "all" members of a species; we aren't told that this specific red butterfly belongs to the "some" group. So, the conclusion doesn't follow from the premise. More importantly, it's not the same as the passage.

C) is wrong because it goes from a probabilistic statement of "can be gained" to concluding that a certain member absolutely exhibits this particular trait when it states "must provide knowledge". The first sentence merely presents us with a statement that denotes a possibility and the argument then concludes a statement that gives us an absolute clause about a member exhibiting that trait definitively. I believe it contains an invalid form of reasoning; however, this isn't the same as the passage.

D) as mentioned above, it is wrong because it presents us with a valid argument by giving us a general principle, then showing that the sufficient condition has been met (after the comma in the final portion of the sentence), and then concludes the necessary condition of the principle, (in the middle of this complex sentence after the semi-colon). Basically:

Premise: "if it's a film directed by R then Dierdre has seen it"
Premise: "film directed by R [Ali: Fear Eats the Soul]").
Conclusion: "Dierdre has seen it [Ali: Fear Eats the Soul]".

Sorry for the long-winded explanation, especially given the fact that this was already addressed sufficiently by one of the experts above, I just find it helpful to write these out in my own words.

E) is wrong because it jumps from a statement about the frequency of a general group of people (skiers) experiencing a high level of risk when it comes to bone fractures to concluding that a member of the group, Lindsey, has likely succumbed to said risk because of the frequency with which she skis ("avid" skier) and the length of time that she has been skiing for ("many" years). But it could be just as likely that she has always had a clean bill of health and has never experienced a bone fracture before from any type of activity, let alone skiing. What if this particular Lindsey, unlike the famous US downhill racer of today’s competitive skiing era, only skis on beginner or bunny-hills? Anyways, all weird coincidences aside, I believe that this argument is invalid. However, it's clearly not the same as the passage, so it's out of the running for that reason.

I hope this is helpful.

[chunsunb]

I picked (D), precisely because it is a valid argument.

The passage presents a valid argument, but (A) doesn't.

The passage is valid because alligators are reptiles; but grass need not be green plants......

[AndyC64]

I am also very confused why D is wrong.

Here is my break down of the logic structure of the stimulus:
==A (a category) has C (certain traits/properties)
==B (an individual) belongs to A (category)
===> Thus, B also has C (certain traits/properties)

Admittedly, answer A is the most correct one. My concern for answer A is that grass is not always green, there can be purple or brown live grass. But since the hidden consensus here does not consider these possibilities, I accept A as the correct answer. However, D is equally correct to me.

==Movies directed by Rainer (a category) is seen by Dierdre (A property);
==Ali:... is a movies directed by Rainer
===> Thus, Ali:... has the property of the movies directed by Rainer. In another word, Ali: ... must be seen by Dierdre.

Is there anything missing in my breakdown of the argument?

Thx in advance!