#22 - No chordates are tracheophytes, and all members of

[jailenea]

Hello, can someone please explain why A is incorrect? I'm not quite understanding the initial reasoning for ruling A out.

[Rachael Wilkenfeld]

Hi jailena,

Here's the stimulus:

C = chordates
T = tracheophytes
P = member of Pteropsida
H = member of family Hominidae

Premise: C T
Premise: P T
(Inference: P C)

Conclusion P H

In order to draw a conclusion that P H, we need to find something that puts H in a category that would rule out P. Our inference above that P C means that if all H are C, P's cannot be H.

Answer choice (A) is something we can't draw that conclusion from because we end up with two premises that don't connect. We'd have P T and H T, but you cannot connect P and H in that scenario. Structurally, you can't connect the two sufficient conditions even if they have the same necessary condition.

All dogs are animals. D A
All cats are animals. C A

We can't connect dogs and cats there. We don't know if all dogs are cats, some dogs are cats, or no dogs are cats. There isn't a way to connect that chain. It's the same structural chain in answer choice (A).

Hope that helps!

[Whatshisface]

Hi!

In the 2022 LR Book, the question I'm having issues with is about the chordates and tracheophytes.

My reasoning/mapping was wrong, and it led me to a confusing inference that made me flip a coin between B and D (I chose D).

Here's how I mapped it out:

C T P H

From there, I transformed the inner connection into a Some "formula" (I now realize this is unnecessary if going from P to C):

C T P H

which led to:

C P H

which brought me to:

C H

And when I got this, I didn't know how to interpret it. "Nothing that is a C is sometimes not an H??"

It's gibberish, so I clearly made at least one mistake in my diagramming. But before I knew it was mistake, it sounded most like Cs are not Hs. But I thought maybe the diagram fully realized would cancel out the negatives, making Cs sometimes/always Hs, thereby making B correct. So, as I said, I guessed.

Also, I know that the book suggests you "plug in" the answer choices into your base diagram, but I'd love to see a way to get to the right answer without working with the answer choice itself, if that makes sense.

[Stephanie Oswalt]

Hi!

In the 2022 LR Book, the question I'm having issues with is about the chordates and tracheophytes.

Hi!

Thanks for the post! I have moved your post to the thread discussing this topic. Please review the explanation on page 1 of this thread and the discussion that follows, and let us know if that helps or if you still have further questions! Thanks!