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

Here's the stimulus:

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

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

Conclusion P :dblline: H

In order to draw a conclusion that P :dblline: H, we need to find something that puts H in a category that would rule out P. Our inference above that P :dblline: 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 :arrow: T and H :arrow: 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 :arrow: A
All cats are animals. C :arrow: 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!

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