Sufficient and Necessary Diagramming help

[jpleu99]

So I'm going through my Lesson 2 HW and finding that I'm having a lot of issues with sufficient and necessary diagramming. I understood it during my online lecture, but then when I got to the homework, it turns out that I didn't understand it.

I always thought that the necessary condition is required in order for the sufficient condition to occur. For example, on pg 2-57, #10, why is "calling the president" a required condition? It's not "necessary" to call the president in order for the package to arrive and for the meeting to be arranged. I thought it was necessary for the package to arrive and the meeting to be arranged in order to call the president? I'm aware that the wording "When" indicates a sufficient condition, but I don't really understand why it is.

I get some questions right, and then on others, I find myself pretty confused as to why one is a sufficient instead of a necessary condition.

[Dave Killoran]

Hi JP,

Thanks for the question! The concerns you are voicing are very normal, so before we get into your question, I'm first going to refer you to some prior posts I've made about conditional reasoning, particularly regarding the use of indicator words and the perils of seeing things as they are in the "real world." I think looking over some of this will answer most (if not all) of your question, and give a better perspective from which to attack all conditional statements. But, if it doesn't solve the problem, we'll come back and parse this one out in detail for you.

• http://forum.powerscore.com/lsat/viewto ... p=216#p216
  
  http://forum.powerscore.com/lsat/viewto ... 6166#p6166

Also, have you checked out the concept discussion module that relates to the lesson? I talk about some of the above ideas in that module.

Please check those out and let me know if they help. Thanks!

[jpleu99]

Thank you so much for the references to other posts! I think I'm getting the hang of conditional reasoning as I'm doing more problems too.

[Dave Killoran]

Great, glad to hear that! If you run into any specific questions, please be sure to post those back here.

Thanks!

[easports]

I just stumbled upon this post & wanted to say thank you so much for additional links you provided & the concept discussion module relating to the lesson. Extremely helpful and provides additional support to the online lecture course and all the book materials I have.

Thank you again!

[Dave Killoran]

Anytime! It's good to know you are finding these useful, and we're always happy to help!

[cls]

Sorry to jump on the coattail of this conversation, but I was hoping to get this clarified. If a statement reads "The only operas that are repeatedly performed over many decades and centuries are those that skillfully explore the human experience." Am I correct and interpreting this as only a necessary statement and hence no full diagram can be drawn?

Thanks!

[Nikki Siclunov]

Hi cls,

Thanks for your question. No condition can be classified as "necessary" unless some other condition can be classified as "sufficient." So let's take a look at your example:

"The only operas that are repeatedly performed over many decades and centuries are those that skillfully explore the human experience."

"Only" is a necessary condition indicator, and in this case it is referring to those operas that skillfully explore the human experience: only those operas are repeatedly performed. So, we can diagram the statement as follows:

Repeatedly performed opera Skillfully explore the human experience

Perhaps not every opera that explores the human experience in this way will be repeatedly performed; however, if an opera is repeatedly performed, then it must skillfully explore the human experience.

Hope this helps!

[cls]

Hi Nikki,

Thanks for your response. That does make sense, but it does leave me with another question. Since "only" is a necessary indicator why is it that the text which follows only is diagrammed as a sufficient? You mention that only refers to operas that explore the human experience. Does that mean one shouldn't assume that an indicator is referring to the words directly following it? I think I'm having a hard time deciphering, which may be which ( S or N) in statements like the above.

Thanks

[Nikki Siclunov]

That's correct: in most cases, the S/N indicator is followed directly by the word or phrase it indicates. This, however, is not always the case. The phrase "the only" is a good example to this exception! It is immediately followed by a sufficient condition, because "only" refers to a clause that appears elsewhere in the sentence. Take the following example:

• The only movies worth watching are those that make me cry.

• Worth Watching Make Me Cry

The condition directly following the phrase "the only" is a sufficient condition, because "only" is referring to the movies that make me cry (necessary).

If this is confusing, keep in mind the following two uses of the word "only":

"only if" immediately precedes a necessary condition
"the only" immediately precedes a sufficient condition

A few more examples:

• The only way to improve is to study hard

=

• You will improve only if you study hard

• Improve Study Hard

Does this help? Let me know.