PrepTest 135

Incorrect. There's no indication that most people in early times lived in urban societies, so we can't support an answer about where "most" people lived.

Incorrect. This answer is about farming, not large-scale farming, and about societies, not urban societies, so it's out of scope.

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
not Nearby large-scale farming → not Early urban society
Other ways of getting food can't support dense urban populations
Large-scale farming → Irrigation → Nearby rivers and lakes

Answer Anticipation:
Two notes on the conditional logic here:
(1) We treated "without" as "if not" here—unless/until/without/except can all be diagrammed this way. If you ended up with the contrapositive of our statement, that's fine!
(2) We chained the last two conditional statements together instead of writing them out separately and then combining them—as you improve at conditional logic, try to make chains as you diagram instead of taking two steps to do so.

Now that we've got the statements written out, we can see a few things. First, there's no clear overlap in terms between the two conditionals, but there are strongly related terms, so we'll circle back to that. Second, the second clause explains the first, but it doesn't really add anything new. It explains why large-scale farming was necessary for early urban society (the contrapositive of our conditional as written), but it essentially reinforces it.

So let's circle back to the conditionals. Since they both talk about large-scale farming, but the opening conditional has that as a negated term, let's take the contrapositive to see if we can chain them together:
Early urban society → Nearby large-scale farming

While the necessary condition here is nearby large-scale farming, that does guarantee that there is large-scale farming. So these do chain together:
Early urban society → Nearby large-scale farming → Irrigation → Nearby rivers/lakes
not Nearby rivers/lakes → not Irrigation → not Nearby large-scale farming → not Early urban society

Let's find an answer that makes a connection supported by this chain.

Answer Explanation:
The contrapositive of the chain tells us that no nearby rivers/lakes guarantees no early urban societies, so this answer is supported and is thus correct.

Key Takeaway:
This takeaway is going to be a bit limited, but we wanted to highlight a trick that the LSAT has pulled several times. Note answer choice (E)—it talks about rural societies when the stimulus discussed urban ones. The LSAT loves to pull that term shift, as many people gloss over that word and don't note the term shift, so always be on the lookout for it when the stimulus uses either term!

Incorrect. This answer isn't about early times, so it's out of scope. Even if it were about early urban societies, those required irrigation (see the conditional chain), which means this answer is contradicted as it applies to those societies.

Incorrect. The stimulus never discusses rural societies, just urban ones, so this answer is out of scope.