LSAT Explanation PT 35, S1, Q22: No chordates are tracheophytes, and all

LSAT Question Stem

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

Logical Reasoning Question Type

This is a Sufficient Assumption question. 

Correct Answer

The correct answer to this question is B. 

LSAT Question Complete Explanation

Let's first analyze the argument in the passage and identify its structure. The passage states:

1. No chordates are tracheophytes (Premise)

2. All members of Pteropsida are tracheophytes (Premise)

3. So no members of Pteropsida belong to the family Hominidae (Conclusion)

In simpler terms, think of chordates as cats, tracheophytes as dogs, and Pteropsida as a specific breed of dogs. The passage is saying that no cats are dogs, and all members of this specific breed of dogs are dogs, so no members of this specific breed of dogs belong to the family of cats.

An "Evaluate" question for this argument could be: "Are all members of the family Hominidae chordates?"

Now, let's discuss the answer choices with respect to the Sufficient Assumption question type, which asks us to find an assumption that, if true, would guarantee the conclusion.

a) All members of the family Hominidae are tracheophytes.

- This choice links Hominidae (H) with tracheophytes (T), but it doesn't help us establish a connection between Pteropsida (P) and Hominidae (H). So, this choice is incorrect.

b) All members of the family Hominidae are chordates.

- This choice links Hominidae (H) with chordates (C). If all H are C, and no C are tracheophytes (T), then no H are T. Since all P are T, it follows that no P are H. This choice guarantees the conclusion, so it is correct.

c) All tracheophytes are members of Pteropsida.

- This choice doesn't help us establish a connection between Pteropsida (P) and Hominidae (H). So, this choice is incorrect.

d) No members of the family Hominidae are chordates.

- This choice would actually contradict the correct answer choice (B) and doesn't help us establish the necessary connection between Pteropsida (P) and Hominidae (H). So, this choice is incorrect.

e) No chordates are members of Pteropsida.

- This choice doesn't help us establish a connection between Pteropsida (P) and Hominidae (H). So, this choice is incorrect.

In conclusion, the correct answer choice is (B): All members of the family Hominidae are chordates. This assumption, when combined with the premises, guarantees the conclusion that no members of Pteropsida belong to the family Hominidae.