PT 36, Section 3, Problem 16 (assumption logic question) Forum

[bman41488]

Hello,

I am having a difficult time deciding between answers A and D (D is correct). There are a few differences between the two answers, but in general, both answers just seem to be opposites (sufficient and necessary conditions are switched).

This situation seems to occur very often. How should I attack each stimulus to make sure that I choose the right answer?

[bk1]

A just says that animals who are capable of complex reasoning have the possibility of making major changes and that animals who are not capable of complex reasoning do not have the possibility of making major changes. With A, it is possible for an animal to have complex reasoning and still not be able to make major changes. Thus, that the reptiles cannot make major alterations does not necessarily mean that they are not complex thinkers.

The conclusion of the argument is such that the assumption which is the answer will somehow make it so that complex reasoning reptiles sometimes make major changes (that they do "not never" do it). Which is D.

[LSAT Blog]

This is a necessary assumption question.

The argument says that because reptiles can't make major changes, they must be incapable of complex reasoning.

NOT Change -> NOT Complex Reasoning


The correct answer is the contrapositive:

if reptiles WERE capable of complex reasoning, they'd be able to make major changes.

Complex Reasoning -> Change


The contrapositive needs to be true in order for the argument to be valid, since they are logically equivalent.


As you noted, Choice A reverses necessary and sufficient conditions.

For a necessary assumption question, look for what must be true in order for the argument to be valid.

For a sufficient assumption question, look for what, if true, would allow the conclusion to logically follow.

You can generally tell the difference between these question-types based upon the verb in the question stem.

Hope this helps,
Steve

[bman41488]

Thank you so much! Your explanations were very helpful