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Lesson help relating to our Advanced Logical Reasoning Course.
 T.B.Justin
  • Posts: 194
  • Joined: Jun 01, 2018
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#62521
Hey,

I have a question regarding the missing links when removing a premise and what would suffice for validity:

P(1): A :arrow: B
P(2): B :arrow: C
P(3): C :arrow: D
C(1): A :arrow: D

If we remove premise (1), are these all the missing links:

A :arrow: B
Not B :arrow: Not A

Further, for a weaken question, would we need to find an answer choice that A or B could likely not occur, or perhaps that B is likely to occur only if A cannot occur.

Also, for a strengthen, under the same pre-tense, find an answer choice that A or B is likely to occur, or perhaps that A's occurrence is unlikely even when B's occurrence is unlikely.

Finally, for an assumption, to defend the argument, we need to find an answer choice that, I could use some help with this one.


Thanks, I must master this test, I appreciate your time.
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 Dave Killoran
PowerScore Staff
  • PowerScore Staff
  • Posts: 4036
  • Joined: Mar 25, 2011
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#62578
Hi T!

I've answered your questions below:
T.B.Justin wrote:Hey,

I have a question regarding the missing links when removing a premise and what would suffice for validity:

P(1): A :arrow: B
P(2): B :arrow: C
P(3): C :arrow: D
C(1): A :arrow: D

If we remove premise (1), are these all the missing links:

A :arrow: B
Not B :arrow: Not A
If you need/intend to connect all the elements, then yes. If skipping elements as possible (which happens too), then A :arrow: C and its contrapositive would also work :-D


T.B.Justin wrote:Further, for a weaken question, would we need to find an answer choice that A or B could likely not occur, or perhaps that B is likely to occur only if A cannot occur.
Assuming all the steps above (A through D) are present, then just killing any one of the statements would call the conclusion into question. For example, if I showed C wasn't necessary to B, that would hurt the argument. Think about it like a real chain—if any one of the links breaks, the whole thing falls apart.


T.B.Justin wrote:Also, for a strengthen, under the same pre-tense, find an answer choice that A or B is likely to occur, or perhaps that A's occurrence is unlikely even when B's occurrence is unlikely.
Again assuming all the steps above (A through D) are present, then just helping any one of the statements would help the conclusion.

T.B.Justin wrote:Finally, for an assumption, to defend the argument, we need to find an answer choice that, I could use some help with this one.
You'd want to find an answers that showed any necessary element was indeed necessary. In other words, protect the basic integrity of the chain. That could very well take the form of showing that none of the relationships are backwards or invalid (meaning they are correct as is, and the answer would show that no relationship is backwards or no relationship is invalid).

Thanks!

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