Logical reasoning PrepTest 114 · Section 1 · Question 20

Incorrect. While drastic shifts in climate always lead to migrations, that doesn't mean that something else doesn't lead to more migration. There could be another sufficient condition for migration that is more frequent or affects larger groups at a time.

Incorrect. First, this answer talks about [a]ll shifts in climate, whereas the stimulus discusses only "[d]rastic shifts." Second, this answer relies on the last statement chaining into the other conditionals, but, as we discussed in our Anticipation, the intermingling of ideas is necessary for rapid advances, not sufficient for progress.

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
(1) Climate and geology determine industry locations
(2) Drastic shift in climate → Migrations
(3) Migrations → Intermingling of ideas
(4) Rapid advances in civilization → Intermingling of ideas

Answer Anticipation:
This stimulus features a series of relationships, most of which are conditional. Let's dig into those, as well as the non-conditional statement.

It opens with that non-conditional statement, showing that the locations where human industry can be established are "determine[d]" by climate and geology. This is important because the word determine means that these are the deciding factors, not just relevant factors. Such a relationship could be used to justify an answer, so we should keep this in mind even though it's not a conditional that can chain into the rest of the statements.

After that, we get three conditionals ("always, bring about, necessary for"). But we need to be careful here! They don't all chain together. The first conditional is introduced with the phrase "always result in", which tells us that the concept preceding that phrase is the sufficient condition—if it always results in an outcome, then it's sufficient to guarantee that outcome. That chains right into the next conditional, which states that the migrations "bring about"—i.e., lead to—an intermingling of ideas.

However, the next statement—despite being in succession in the stimulus itself—doesn't chain together. Migrations are sufficient to lead to an intermingling of ideas, but those ideas are necessary for rapid advances in civilization. That intermingling of ideas is a necessary condition in each conditional.

This means that we can only chain statements 2 and 3 together:
Drastic shift in climate → Migrations → Intermingling of ideas
not Intermingling of ideas → not Migrations → not Drastic shift in climate

This chain may interact with the other two statements in some way to lead to a correct answer, but that's not something we can anticipate, so let's head to the answers with these statements outlined.

Answer Explanation:
This answer is the contrapositive of the second conditional: not Migrations → not Drastic shift in climate. If a population is settled, then it's not migrating; if the climate is fairly stable, then there aren't drastic shifts. Since this answer essentially restates a statement from the stimulus, it must be true and is thus correct.

Key Takeaway:
Be careful with your diagrams for Must Be True conditional statements! While most of the time the statements will chain together, the LSAT loves to throw curveballs at you in these later questions, which can mean that you'll get two statements that share a term but can't be chained together, as we saw here. Actively think through the conditional indicator word and what it means for the sentence.

Incorrect. There's no discussion of populations settling in every place where industry can be established—that's way too broad.

Incorrect. Every migration is accompanied by an intermingling of ideas which is necessary for rapid advances. The intermingling of ideas would need to be sufficient for rapid advances for this answer to be supported.