PrepTest 143, Section 3, Question 16
Theorist: To be capable of planned locomotion, an(47 more words not shown)
The theorist's argument is flawed(3 more words not shown)
- Aconfuses a necessary(11 more words not shown)
- Btakes for granted(19 more words not shown)
- Cpresumes, without providing(20 more words not shown)
- Dtakes for granted(14 more words not shown)
- Epresumes, without providing(20 more words not shown)
Reading the argument
Having the equipment you need doesn't guarantee you can do the job.
First, let's translate the description. “Planned locomotion” means moving from place to place in a planned way. The organism must represent its surroundings internally and send messages that control its muscles. The theorist says doing those things requires a central nervous system.
That makes the nervous system a requirement. It doesn't make the nervous system enough. Imagine an organism that has one but can perform only one of those two tasks, or that faces some other obstacle to planned movement. It could have the system without being capable of the movement.
What we’re looking for
The conclusion rules out that possibility: no planned movement, therefore no central nervous system. To describe the flaw, keep the direction straight. We've been told the capacity requires the system, not that possessing the system guarantees the capacity.
Working the answers
- ACorrect
The necessary condition is having a central nervous system; the capacity is planned locomotion. The theorist treats the requirement as though it were enough to guarantee the capacity. That is why the theorist thinks the absence of the capacity rules out the system itself. But something else needed for planned movement could be missing even when a central nervous system is present.
- B
Sending muscle messages is only one ability discussed in the passage. The organism also needs an internal representation of its environment. B focuses on treating the muscle-message ability as enough for locomotion, whereas the conclusion makes the broader leap from lacking planned locomotion to lacking a central nervous system altogether. It doesn't identify the precise system-versus-capacity confusion that A does.
- C
An internal representation could have other useful purposes, such as helping an organism recognize a threat. The theorist doesn't deny that. The argument concerns what an organism needs for planned movement, not whether movement is the only benefit of understanding its surroundings.
- D
Nothing here explains how an adaptation originally developed. A feature could have arisen for one purpose and now serve another without resolving the argument's mistake. The question concerns what possessing a central nervous system establishes about a present ability.
- E
We aren't told that even a very simple nervous system can form the required representation. In fact, that would be one possible limitation to ask about. But the theorist's mistake doesn't depend on any particular level of complexity: it treats having the system as enough, without establishing everything else needed for the capacity.
More Flaw questions
Learn the LSAT our way
Our platform drills Flaw questions at your level and adjusts as you improve.