Logical Reasoning

PT152 · S2 · Q19 Some species of tarantula

A free, expert breakdown of this official LSAT Logical Reasoning question.

  • Save & drill this skill — build targeted practice sets from questions like this one

  • Video walkthroughs — watch every question solved step by step

  • 81 official LSATs — as questions, timed sections & full-length tests

Start practicing free

Some species of tarantula make good pets.

Evidence

(Because there are quantifiers / conditional indicators / repeating ideas, it makes a lot of sense to turn this argument into Algebra)

Some tarantula's make good pets. Some A's are B.

No creature with poison No C's are B. fangs makes a good pet.

Conclusion

Not all tarantula's have poison fangs. Not all A's are C.

Evaluate

We don't really need to judge the validity of the logic here, but it is sound, for what it's worth.

Premise 2 says that "if poison fangs, then not good pet", which contraposes into "if good pet, then not poison fangs".

Thus, since Premise 1 says that "Some tarantulas make good pets", we can infer that "Some tarantulas do not have poison fangs".

Since this argument is using two negative quantifiers (no / not all), it's worth re-capping the negative to positive translations.

No A's are B = All A's are ~B Few A's are B = Most A's are ~B Not all A's are B = Some A's are ~B

At any point on LSAT they might trade one form for the other, and they're perfectly interchangeable.

We wrote our argument as

Premise 1: Some A's are B. Premise 2: No C's are B. Conclusion: Not all A's are C.

But we could have written it interchangeably as

Premise 1: Some A's are B. Premise 2: All C's are ~B. (All B's are ~C). Conclusion: Some A's are ~C.

Goal

We know we need two premises and one conclusion.

The two premises should be a mix: 1 some / not all claim 1 no / all claim

The conclusion is a some / not all claim.

Assuming an answer has those basic ingredients, we'll make sure that the Some / Not All premise gives us an idea that triggers the No / All premise.

19.

Which one of the following arguments is most similar in its pattern of reasoning to the argument above?

  1. Correct

    None of the poetry written

    Why this is right

    Our two premises are None and Some, and our conclusion is Some, so this is worth reading. Premise 1: Some A's are B. Some poems in this collection have a regular meter. Premise 2: No C's are B. No written by Strawn have regular meter. Conclusion: Not all A's are C. Some poems in this collection are ~written by Strawn. (Some A's are ~C) Everything matches up!

    Skill tested: Parallel · how this choice captures the argument's function is the move to repeat next time.

    55% picked this

  2. Some of the poems in

    Bad Premise Match

    Our two premises are Some and Some, so there's no need to read this one. We needed a Some/Not All premise and a No/All premise. Premise 1: Some A's are B. Premise 2: No C's are B. Conclusion: Not all A's are C. (Some A's are ~C)

    11% picked this

  3. Some of the poetry written

    Invalid Logic Bad Conclusion Match

    Our two premises are Some and No, and our conclusion is Not All, so this is worth reading. Premise 1: Some A's are B. Some WBS is RM. Premise 2: No C's are B. No PIC is WBS. Conclusion: Not all A's are C. Some PIC are ~RM. (Some A's are ~C) (PIC = poems in this collection) (RM = regular meter) (WBS = written by Strawn) The logic on this one doesn't work. The 2nd premise is a conditional that says, PIC → ~WBS WBS → ~PIC Does the 1st premise talk about PIC or WBS? Yes, it says, "Some RM is WBS", which allows us to conclude "Some RM is ~PIC". So the correct conclusion that should have been drawn is, "Some poetry with regular meter is not in this collection" also known as "Not all poetry with regular meter is in this collection". Instead, we got a conclusion saying "Not all poetry in this collection has regular meter" also known as "Some poetry in this collection does not have regular meter". Saying "some poetry with regular meter is not in this collection" is not the same thing as saying "some poetry in this collection does not have regular meter". "Some people at my party have not been to Mars" is a different claim from saying "Some people who have been to Mars were not at my party"

    28% picked this

  4. Some of the poems in

    Bad Conclusion Match

    Our two premises are Some and None, but our conclusion is only, which is the same strength as No/All (conditional). So there's no need to read this one. The conclusion also brings in a brand new idea, unpublished poetry by Strawn. Premise 1: Some A's are B. Premise 2: No C's are B. (this answer choice) Conclusion: Not all A's are C. vs. Only D is B (Some A's are ~C)

    4% picked this

  5. No poems with a regular

    Bad Premise Match

    Our two premises are No and None, so there's no need to read this one. We needed a Some/Not All premise and a No/All premise. Premise 1: Some A's are B. Premise 2: No C's are B. Conclusion: Not all A's are C. (Some A's are ~C)

    1% picked this

Continue the review in LSAT Lab

Save this question, watch the video walkthrough, and drill similar questions in your LSAT Lab account.

Save and practice this skill
LSAT Lab

Turn this review into a targeted study plan.

Save this question, drill more like it, watch the video walkthrough, and track your progress in your LSAT Lab account.

Start practicing free