Hi kingz,
There's a mixture of causal and conditional reasoning in this stimulus that is throwing you for a loop in your diagramming. The premises definitely state a line of conditional relationships, and those relationships can be diagrammed as you've correctly done (Flight
Stable
Balance
Ligament). The correct answer (and best conclusion) is indeed answer choice E, which states a
causal relationship. A "means" is something that activates, or allows for, a certain result. The ligament is the thing that allows for the stability the bird needs. So the relationship implied by answer choice E is not a conditional relationship, and it doesn't need to be harmonized with your diagramming chain. A very good question to ask is "how can we derive this causal relationship from what looks like a bunch of conditional statements?" Look at the last sentence of the premise chain, where it says "the only structure
capable of balancing them [the forces] is a ligament." So not only is the ligament
necessary (because it's the
only thing available for the stated purpose), but it also has some
causal power as well. In other words, the ligament is the thing that is
providing the balance (it has a
capacity, which is a
causal power). Thus, answer choice E is validated by the phrase "capable of balancing." We don't need to diagram the relationship, or harmonize it with the conditional diagram. We simply need to see that the causal relationship is validated by the (causal) phrasing of the last premise.
I hope this helps!
Jeremy Press
LSAT Instructor and law school admissions consultant
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