Q15 - The only plants in the garden

[sheffieldjordan]

I don't understand why the reasoning in this question stem is "faulty." Could someone please clarify it for me?

I thought, for example:

PIG --> T
(PIG: plants in the garden, T: tulips)

oh, but wait, all the tulips are tall tulips, therefore

PIG --> TT
(PIG: plants in the garden, TT: tall tulips)

What am I overlooking that makes this reasoning faulty?

Also, I read on PowerScore that only 49% of original test takers got this answer correct, choosing (c). And 29% chose (a).

I chose (c) after seeing it and quickly dismissed (a). Why would (a) be so appealing?

Thanks to any and all who can help me with this!

[elizabeth.r.casanova]

Hi Jordan! I could be incorrect, but I believe the argument is faulty because it utilizes circular reasoning. As you likely know, circular reasoning is when the supporting evidence's meaning is equivalent to the conclusion's meaning. In #15, the second sentence does not offer any additional information that we did not acquire after reading the first sentence.

Like you, I did not struggle choosing between (A) and (C). Yet, my guess for those that did choose (A) did not notice that the stimulus used "plants" twice and (C) used "primates" twice in their so-called 'conclusions.' If you add "dogs" behind the last word in choice (A), it too would have been a correct answer choice.

Hope this helps!

[bbirdwell]

Ah, close, Liz! However, it's not quite circular, as the conclusion differs from the premise in a subtle and important way. You are pointing right at that subtle difference with your last comment about the words "dogs" and "primate," though I'm not sure you totally latched onto the significance.

Here's the key question to ask when thinking about this problem:
is a tall tulip necessarily a tall plant?

Here's another example to illustrate:
The only animals in the cage were mice, but they were huge mice. So, the only animals in the cage were huge animals.

Subtle, huh? The assumption that a huge mouse is a huge animal is not a valid one, and that is the flaw that (C) repeats and (A) does not.

Why do people choose it? Who knows! I suspect people choose it because it's very, very close to being correct, and it's the first option, so perhaps it becomes people's favorite right away and they fail to see the other choices critically.

Hope that helps!

[elizabeth.r.casanova]

Brian,

My gosh, so subtle! Thank you much for responding rapidly, correcting my misunderstanding, and using an analogy for further explanation. I definitely understand the flaw now. Thanks again!

[tzyc]

I still do not see the flaw in the stimulus....
Doesn't it say the only plant=tulips?
So tulips are plants...
And it says they were all tall.
Thus, the only plant=tulips=tall, so there are only tall plants...
I'm confused

[griffin.811]

I was pleasantly surprised when I was able to pick up on the issue here.

Stim: The only plants in the garden are tall tulips, so the only plants in the garden were tall ones.

(notice subject shifts from tulips to plant )

Analogy: The only school buses in the lot were fast ones, so there were only fast vehicles in the lot.

Just because the school buses are fast for school buses doesn't mean they are fast when compared to the wider subject of all vehicles. The fastest school bus is not faster than a Ferrari etc...

Similarly, tulips, while maybe tall compared to other tulips, or even other flowers, are not tall when compared to the Redwoods, or any other tree, which are considered plants as well.

[Twitch]

Whoa... this is a tough one! This might be the toughest LR problem I've run across thus far!

I got the right answer by following the structure of the argument, but I really didn't see the flaw until I had read multiple explanations several times.

So essentially, the flaw is that the construction of the argument tempts us to read "tall plants" in the context of the argument itself, but in reality "tall plants" is supposed to be understood in the context of objective reality, where even a tall tulip is not an objectively tall plant.

The connection to answer choice C becames clear when I realized that, since even a small gorilla is not an objectively small primate.

[WaltGrace1983]

This was one is crazy! I didn't like it at all though the right answer seemed better than the wrong ones so I just had to go with my gut on this one.

P → T → TT ⊢ P → TP

I guess one could understand this most effectively by just seeing that it goes from talking about a tall tulip to a tall plant. Tricky!

(A) DS → P → B ⊢ DS → B
Perfectly logical.

(B) BB → (OB or RT) & T ⊢ BB → T
This one doesn't seem flawed at all either. It almost seems circular (but not quite) as it says that "all the buildings on the block were tall" so "all the office buildings on the block were tall." There isn't really too much to reason out here. According to the premises, if the building is on the block it MUST BE tall and, thus if an office building is on the block, it too must be tall. Not flawed.

(C) PZ → G → SG ⊢ PZ → SP
This has the same flaw. Just because something is a small gorilla doesn't mean that something is a small primate. In my uneducated opinion, I might say that a small gorilla is still a pretty freakin' big primate!

(D) FK → P → ~R ⊢ FK → ~R
Perfectly logical! Just like (A).

(E) GP → (L & H) ⊢ L → H
I might be wrong (someone correct me if so) but this seems to be a correlation/causation flaw. Just because there is a set of objects that are both large and heavy doesn't mean that being large causes being heavy, or that everything large is heavy. There also seems to a bit of a scope shift going on here. We are talking about grand pianos and yet we use that as evidence for everything.

[onguyen228]

Error of composition at its finest!

If you try to ignore the formal logic illusion, you might be able to see what I mean. The formal logic is there just to make the stimulus convoluted.

The characteristic of a subgroup (tulips) is applied to the group as a whole (plants).

Just because a subgroup has a relative characteristic does not prove that the group as a whole has the same relative characteristic.