Any advice on Justify/2S questions

[e10]

For some reason, I really struggle with these questions. I know PS says that if new information is presented in the conclusion it will most likely be in the answer choice, information in the premises and conclusion will most likely not be in the correct answer, and info in a premise not in the conclusion can be in the right answer choice. However, with using these techniques I still cannot move away from these questions feeling that I got it right. Any advice would be appreciated.

[LSAT Blog]

These are one of the few question-types often worth diagramming.

The following 3 examples are the most common format for these types of questions, but not the only format. The correct answer to a Sufficient Assumption (Justify) question is often simply a restatement or the contrapositive.

I'm going over the most common format with formal logic, then with a few examples from real PT questions:

Evidence: A ---> B
Conclusion: C ---> B

Sufficient Assumption #1: C ---> A
Sufficient Assumption #2: NOT A ---> NOT C

Contrapositively...

Evidence: D ---> E
Conclusion: D ---> F

Sufficient Assumption #1: E ---> F
Sufficient Assumption #2: NOT F ---> NOT E



Examples:
PrepTest 31 (June 2000), Section 2, Question 10, p91 in Next 10

Evidence: JR ---> NOT D
Conclusion: FP ---> NOT D

Sufficient Assumption: FP ---> JR


PrepTest 35 (October 2001), Section 1, Question 22, p226 in Next 10

Evidence: P -> T -> NOT C OR C -> NOT T -> NOT P
Conclusion: P ---> NOT H OR H ---> C

Sufficient Assumption: NOT C ---> NOT H
Sufficient Assumption: H ---> C


PrepTest 35, Section 4, Question 14, p244 in Next 10

Evidence: Struggle Early -> Good Perspective = SE -> GP

Conclusion: Struggle Early -> NOT Success Granted = SE -> NOT SG


Sufficient Assumption: GP -> NOT SG (Choice B)



The most common formats for Justify the Conclusion (aka Sufficient Assumption) questions, are (in order of complexity):

1. broad principle / restatement of conclusion / arg
2. contrapositive of conclusion / arg
3. the format in the post I linked above

I've found the 3rd format to be the most common.


I think of Sufficient Assumption Qs as providing information that, if true, would be Sufficient to guarantee the argument's validity.

HTH