Sufficient and Necessary Diagramming Drill (2-37)

[tomoko]

Question 21: Buying scalped tckets is the only way for Jim to get into the concert.

I understand that in this sentence, "only" does not indicate a necessary condition (NC), it only modifies "way".

My question is how do you know which part of the sentence becomes a sufficient conditon (SC)? I put S (buying scalped tikets) -> JC (Jim gets into concert).

I am little confused which part of the sentence beome SC or NC without the indicators (2-7) in a sentence.

Is there any way for me to know which part of the sentence becomes SC or NC without indicators present in the sentence?

[Nikki Siclunov]

Thanks for your question. The word "only" always indicates a necessary condition, and the example you bring up is no exception. Yes, "only" refers to "way," which in turn refers to "buying scalped tickets" (buying scalped tickets is the only way).

Your representation of the conditional relationship implies that if Jim buys scalped tickets, he will get into the concert. This is clearly a false inference: just because there is only one way to accomplish a particular goal does not mean that this one way is guaranteed to accomplish it. However, since buying scalped tickets is the only way to get into the concert, we do know that if Jim does get in, he must have bought such tickets.

Sometimes, it is helpful to think about the inherent meaning of the statement and conceptualize the distinction between sufficient and necessary conditions in terms dependence. The sufficient condition depends on the necessary condition, but not the other way around. In the example you mentioned, getting into the concert depends on buying scalped tickets, which is why "buying scalped tickets" is a necessary condition, and the remainder - a sufficient condition.

Hope this helps!

[tomoko]

Thank you, Nikki, for your help.

In the future, I'll try to put "If.. then" sentence as you did for my example. That was very helpful explanation!

[hl205136]

I have been doing these drills and I constantly mix up sufficient and necessary.
The thinking I keep having is: If [blank] then [blank]. I do not believe this is correct.
In different words in the book, how do I identify what is sufficient and what is necessary?
Also in different words can you define a sufficient and necessary condition?

[Dave Killoran]

I have been doing these drills and I constantly mix up sufficient and necessary.
The thinking I keep having is: If [blank] then [blank]. I do not believe this is correct.
In different words in the book, how do I identify what is sufficient and what is necessary?
Also in different words can you define a sufficient and necessary condition?

Hi HL,

This is a topic that has come up hundreds of times before on this Forum, so fortunately we have had a chance to write about it frequently. So, I'm going to start by referring you to some prior discussions of conditional reasoning, including an analysis of intuition vs technical knowledge:

• Avoid Real World Interpretations and Follow the Language: http://forum.powerscore.com/lsat/viewto ... p=216#p216
  
  One More Look on what Sufficient and Necessary Means (this is key so that when indicators aren't present, we know what we're doing): http://forum.powerscore.com/lsat/viewto ... 6166#p6166
  
  LSAT Conditional Reasoning: When To Diagram: http://blog.powerscore.com/lsat/bid/333 ... To-Diagram
  
  The PowerScore LSAT Blog, Conditional Reasoning articles - http://blog.powerscore.com/lsat/topic/l ... -reasoning. We write often about this concept, and there are over 20 articles here discussions all sorts of interesting conditional language and arrow relationships.

This is just a small selection of the items we've published on this topic, so I encourage you to go beyond these and explore even more. I frequently write about conditional reasoning since it's so prevalent on the LSAT, so if you search my posts you can find me talking about it quite a bit.

Please let me know if that helps. Thanks!