Sufficient and necessary condition help. Forum

[Chowfun]

I am sort of panicking. I am going to take the June 2013 test. I am studying now for the LSAT. I am completely stumped on S&N Conditions. I understand the rules, I know how to apply them, but for some reason I get confused. Sometimes when abbreviating the S&N cond. I forget what the abbreviation I wrote stood for. Sometimes I get confused when working out the answer choices. Other times I give up because I have taken so much time on the problem and I'm frazzled. I do get the answer when I work at it and not give up, but S&N cond. sometimes get so confusing that it makes me angry. Is there a faster method to doing these sorts of problems, because I can never see me getting the answer in this 1:45 time frame.

Can anyone give me advice? I'm have decided I will do everything I can to beat this test, but I feel like I'm fighting a losing battle.

[Chowfun]

For example,"If the city council maintains spending at the same level as this year's, it can be expected to levy sales tax of 2 percent next year. Thus, if the council levies a higher tax, it will be because the council is increasing its expenditures."

So I set up the question and simplify the S&N conditions, but for some reason I am not understand the purpose or something isn't clicking that when I go to answer the question I'm frazzled. Ugh, I really am confused. I think so confused that I can feel a blockage of some sort.

[CardozoLaw09]

In response to your example; if X happens, then Y happens. And if Y happens then Z happens.

What comes after the "If" is your sufficient condition that guarantees the necessary condition - in this case, the council maintaining its spending level is sufficient, or guarantees, that they will levy a higher tax. If they levy a higher tax, then that guarantees that it will be because the council is increasing expenditures.

Conditional logic:

X ---> Y [conditional claim 1]

Y ---> Z [conditional claim 2] *the "Y" in claim 1 is equivalent to the "Y" in claim 2, although they are worded differently; levying a sales tax of 2 percent next year = council levying a higher tax

Now that you have your conditional framework set up, you can move onto the answer choices. Note that it's not too difficult to juggle these two conditional statements in your head if you are comfortable with conditional logic.

If you're looking for a necessary assumption then an answer choice that regurgitates one of the necessary conditions (Y or Z) would be correct. If you're looking for a sufficient assumption then the answer choice will be a restatement of the conclusion or a restatement of conditional claim 1. Both of these would be sufficient assumptions because they facilitate the conclusion of the argument. Also, the sufficient assumption could be the contrapositive of either of the two conditional claims or it could be a general principle that encompasses the conclusion of the argument ie) Anytime a higher tax is levied, it can be assured that it is because expenditures are increasing. In addition, anytime a new term is introduced in the conclusion of the argument, then always look for that new term in one of the answer choices if you are dealing with a sufficient assumption question.

Drilling and becoming comfortable with conditional logic are essential if you want to master these question types. Manhattan has a couple chapters that does a great job in concisely explaining both concepts.

[nugnoy]

I am sort of panicking. I am going to take the June 2013 test. I am studying now for the LSAT. I am completely stumped on S&N Conditions. I understand the rules, I know how to apply them, but for some reason I get confused. Sometimes when abbreviating the S&N cond. I forget what the abbreviation I wrote stood for. Sometimes I get confused when working out the answer choices. Other times I give up because I have taken so much time on the problem and I'm frazzled. I do get the answer when I work at it and not give up, but S&N cond. sometimes get so confusing that it makes me angry. Is there a faster method to doing these sorts of problems, because I can never see me getting the answer in this 1:45 time frame.

Can anyone give me advice? I'm have decided I will do everything I can to beat this test, but I feel like I'm fighting a losing battle.

It depends. If you are OK with getting by half the time you can just notice a missing link and connect it. For example, a lot of assumption questions have a structure where P talks about A, then C concludes in B. So with those you can just find the answer that says If A then B (or if not B then not A).

The problem with this is that it'll be ok for maybe 33% to half the time, but it'll be super frustrating on questions that have wrong answers that mention both A and B but just have them in a different order. And I think S&N is such a ubiquitous concept that it's better to understand it rather than leave it shaky.

The best way is to understand S&N and naturalize the concept. If you're getting confused, that means you're NOT understanding the rules well enough or you DON'T know how to apply them well enough. That's totally fine, just take it slow and don't let it get to you.

Here's roughly how I got comfortable with S and N
1. Learned the concept
2. Did a lot of drills
3. Started thinking about what the symbols mean, what one diagram allows/prohibits/does not say.
4. Started thinking many things in terms of S&N (for example if I'll see a sign that says "no parking any time on this street" I think, "if I know there's parking on a street, it's not this street. If I know that I'm talking about/I'm on this street, I know there's no parking here."

If you forget the abbreviations, then don't abbreviate for now. Write everything out. After you're more comfortable you can abbreviate it. I used to write everything out word for word. Now I just write the first letter of each important word - and it's no problem anymore. In fact you won't need to diagram it once you become familiar with S and N concept. But getting there requires a lot of grind.

And depending on how comfortable you are with the material and what score you have set as a goal I think it's totally fine to take it in October or November. I took it once not fully prepared and that was just wasted money and a number that I don't need but will appear on my record when I apply.

Maintain -> levy 2%
NOT(levy 2%) -> Not(maintain)

I can't say much more b/c I don't know its context. It seems a little off though - the premise is S&N-esque, but the wording is a little weak with "it can be expected" and not "it will levy 2%." Also, not maintaining a budget doesn't necessarily mean increasing expenditures, it could be suffering from decreased revenue.

Oh, BTW it goes from a S&N premise to causal conclusion. I don't think that's right, esp when the cause wasn't mentioned in the premise (maintaining budget vs increasing expenditure)

[Chowfun]

I am sort of panicking. I am going to take the June 2013 test. I am studying now for the LSAT. I am completely stumped on S&N Conditions. I understand the rules, I know how to apply them, but for some reason I get confused. Sometimes when abbreviating the S&N cond. I forget what the abbreviation I wrote stood for. Sometimes I get confused when working out the answer choices. Other times I give up because I have taken so much time on the problem and I'm frazzled. I do get the answer when I work at it and not give up, but S&N cond. sometimes get so confusing that it makes me angry. Is there a faster method to doing these sorts of problems, because I can never see me getting the answer in this 1:45 time frame.

Can anyone give me advice? I'm have decided I will do everything I can to beat this test, but I feel like I'm fighting a losing battle.

It depends. If you are OK with getting by half the time you can just notice a missing link and connect it. For example, a lot of assumption questions have a structure where P talks about A, then C concludes in B. So with those you can just find the answer that says If A then B (or if not B then not A).

The problem with this is that it'll be ok for maybe 33% to half the time, but it'll be super frustrating on questions that have wrong answers that mention both A and B but just have them in a different order. And I think S&N is such a ubiquitous concept that it's better to understand it rather than leave it shaky.

The best way is to understand S&N and naturalize the concept. If you're getting confused, that means you're NOT understanding the rules well enough or you DON'T know how to apply them well enough. That's totally fine, just take it slow and don't let it get to you.

Here's roughly how I got comfortable with S and N
1. Learned the concept
2. Did a lot of drills
3. Started thinking about what the symbols mean, what one diagram allows/prohibits/does not say.
4. Started thinking many things in terms of S&N (for example if I'll see a sign that says "no parking any time on this street" I think, "if I know there's parking on a street, it's not this street. If I know that I'm talking about/I'm on this street, I know there's no parking here."

If you forget the abbreviations, then don't abbreviate for now. Write everything out. After you're more comfortable you can abbreviate it. I used to write everything out word for word. Now I just write the first letter of each important word - and it's no problem anymore. In fact you won't need to diagram it once you become familiar with S and N concept. But getting there requires a lot of grind.

And depending on how comfortable you are with the material and what score you have set as a goal I think it's totally fine to take it in October or November. I took it once not fully prepared and that was just wasted money and a number that I don't need but will appear on my record when I apply.

Maintain -> levy 2%
NOT(levy 2%) -> Not(maintain)

I can't say much more b/c I don't know its context. It seems a little off though - the premise is S&N-esque, but the wording is a little weak with "it can be expected" and not "it will levy 2%." Also, not maintaining a budget doesn't necessarily mean increasing expenditures, it could be suffering from decreased revenue.

Oh, BTW it goes from a S&N premise to causal conclusion. I don't think that's right, esp when the cause wasn't mentioned in the premise (maintaining budget vs increasing expenditure)

Thank you for your advice. I think you are right maybe I don't understand the rules like I think I do. I only understand them when it comes time to diagram, but when it's time to move a step further I freeze.

The question isn't off - well, it might be, but I got it straight from a previous LSAT so I doubt it. The same problems you are having with understanding the question are mine as well and then some.

For instance, I can properly conclude MS--->2% and the contrapositive is (no)2%----> (no)MS. Conclusion: CHT (council Higher tax)----> CIE(council increase expenditures) Contrapositive---> (no) CIE---> (no)CHT). Although I do not understand what I am writing. I honestly do not understand the question. I don't understand the premise or conclusion. I think the LSAT asks questions that are above my intellect. lol I guess I'm not as smart as I thought I was.

I didn't know there was a November LSAT. I'll probably push back my test date to October if this is the case. I can then take it in November and I will have more time to study. Right now I put in over 5 hours a day. On top of work, class and ec's.

Ugh... now off to continue to work on this problem till I am blue in the face.

[Chowfun]

In response to your example; if X happens, then Y happens. And if Y happens then Z happens.

What comes after the "If" is your sufficient condition that guarantees the necessary condition - in this case, the council maintaining its spending level is sufficient, or guarantees, that they will levy a higher tax. If they levy a higher tax, then that guarantees that it will be because the council is increasing expenditures.

Conditional logic:

X ---> Y [conditional claim 1]

Y ---> Z [conditional claim 2] *the "Y" in claim 1 is equivalent to the "Y" in claim 2, although they are worded differently; levying a sales tax of 2 percent next year = council levying a higher tax

Now that you have your conditional framework set up, you can move onto the answer choices. Note that it's not too difficult to juggle these two conditional statements in your head if you are comfortable with conditional logic.

If you're looking for a necessary assumption then an answer choice that regurgitates one of the necessary conditions (Y or Z) would be correct. If you're looking for a sufficient assumption then the answer choice will be a restatement of the conclusion or a restatement of conditional claim 1. Both of these would be sufficient assumptions because they facilitate the conclusion of the argument. Also, the sufficient assumption could be the contrapositive of either of the two conditional claims or it could be a general principle that encompasses the conclusion of the argument ie) Anytime a higher tax is levied, it can be assured that it is because expenditures are increasing. In addition, anytime a new term is introduced in the conclusion of the argument, then always look for that new term in one of the answer choices if you are dealing with a sufficient assumption question.

Drilling and becoming comfortable with conditional logic are essential if you want to master these question types. Manhattan has a couple chapters that does a great job in concisely explaining both concepts.

Oh gosh you have cleared up the serious blockage I had in my head. I wasn't understanding the wording of the question, which in turn led to me not being able to draw the correct inference. Thank you so much. I do see where *the "Y" in claim 1 is equivalent to the "Y" in claim 2, although they are worded differently; levying a sales tax of 2 percent next year = council levying a higher tax, but I wouldn't not have come to that conclusion if you did not tell me. The reason why is because the question read, "it can be expected to levy a sales tax of 2 percent next year". How is that equivalent to levies higher tax? Ugh...I kind feel silly.

[Jeffort]

There is no November LSAT administration in addition to the October one.

The other poster probably listed November because a few years ago (forgot which year), the typically October administration was in the beginning of November that year instead of October.

Part of your confusion might have to do with trying to make sense of the topic the conditional relationships are disguised in and why one particular element would in the real world require the other. If that is the case and you were trying to understand why maintaining the same spending level would require them to increase taxes, you are over thinking what you need to worry about. Stuff of that sort doesn't matter on the LSAT. One element requires the other merely because a premise (which you must accept as factually true whether or not it is in the real world) says so.

Your job to solve the questions properly is simply to identify the conditional relationships that are established and then to analyze/reason within them properly according to the rules of valid conditional reasoning and/or to identify flawed reasoning that uses an established conditional relationship in a logically flawed way.

Try not to over think conditional reasoning, it is pretty straightforward and mechanical once you get used to it. Do not worry about questioning the truth of premises, just analyze the way they are mechanically linked up in order to attempt to prove that the conclusion is 100% guaranteed to be true. Pay attention to logical form over the subject matter/substance of the argument, the subject matter is just the veneer the pattern of reasoning is packaged in and is frequently chosen to distract you and make the problem seem harder than it really is.

The farthest you have to go when thinking about the subject matter is understanding what each described element is in a basic sense so that you can identify when it is referred to with different wording in a second or third part of the argument or in answer choices and also understanding what basic common sense stuff goes along with and is fair game to use in the analysis of any described element that is a common sense/pedestrian type of thing everyone in college or beyond is expected to know (such as water is a liquid and it gets things wet or people watch shows and movies on TVs, etc.). The LSAT writers love to paraphrase the same elements (use different words or phrases to say/refer to the same thing) in order to throw people off (especially people that try to solve problems simply with keyword matching). Simple example: "There is moisture on the road" means the same thing as "The street is wet".

Can you supply the reference (PT#, section # & Q#) for the argument you paraphrased so we can take a look at the exact question? Every single word and phrase exactly how they are phrased is critical for proper analysis since things that matter sometimes get left out or changed when people paraphrase and post question content.

[nugnoy]

Oh god I meant the December haha. Sorry for the confusion!

[gaud]

http://plato.stanford.edu/entries/necessary-sufficient/

[Chowfun]

There is no November LSAT administration in addition to the October one.

The other poster probably listed November because a few years ago (forgot which year), the typically October administration was in the beginning of November that year instead of October.

Part of your confusion might have to do with trying to make sense of the topic the conditional relationships are disguised in and why one particular element would in the real world require the other. If that is the case and you were trying to understand why maintaining the same spending level would require them to increase taxes, you are over thinking what you need to worry about. Stuff of that sort doesn't matter on the LSAT. One element requires the other merely because a premise (which you must accept as factually true whether or not it is in the real world) says so.

Your job to solve the questions properly is simply to identify the conditional relationships that are established and then to analyze/reason within them properly according to the rules of valid conditional reasoning and/or to identify flawed reasoning that uses an established conditional relationship in a logically flawed way.

Try not to over think conditional reasoning, it is pretty straightforward and mechanical once you get used to it. Do not worry about questioning the truth of premises, just analyze the way they are mechanically linked up in order to attempt to prove that the conclusion is 100% guaranteed to be true. Pay attention to logical form over the subject matter/substance of the argument, the subject matter is just the veneer the pattern of reasoning is packaged in and is frequently chosen to distract you and make the problem seem harder than it really is.

The farthest you have to go when thinking about the subject matter is understanding what each described element is in a basic sense so that you can identify when it is referred to with different wording in a second or third part of the argument or in answer choices. The LSAT writers love to paraphrase the same elements (use different words or phrases to say/refer to the same thing) in order to throw people off (especially people that try to solve problems simply with keyword matching). Simple example: "There is moisture on the road" means the same thing as "The street is wet".

Thank you so much. This helped. I do have a tendency to over think things and question everything. This helps me a lot. I will also be aware of different wording because I was trying to keyword match.

[Chowfun]

Oh god I meant the December haha. Sorry for the confusion!

haha it's okay. Do most colleges accept December LSAT? Is that the last one they will take?

[gaud]

Yes, they will accept your December LSAT. February is the last one most schools take.

[Chowfun]

Yes, they will accept your December LSAT. February is the last one most schools take.

Yea this is true, but my top school, which I am applying ED for won't take LSAT's later than October.

I took this from their Fall 2012 App. I don't know if they have changed this since.
"Early Decision Applicants must take the LSAT no later than October 2011.

[gaud]

Well, you didn't qualify your statement. Most schools have ED deadlines that December-takers will not be able to meet.

[Chowfun]

Well, you didn't qualify your statement. Most schools have ED deadlines that December-takers will not be able to meet.

lol. So June it is then! I wonder if 4 months will be enough? I feel as though I need a full year..the way this S&N is going. I'm pulling an all night until I understand this stuff. This is my third day studying and it's already going down hill.

[gaud]

4 months should be fine. Check out one of the guides posted in this forum (Pithypike's, NoodleyOne, etc.). They are all great.

Good luck!

[Chowfun]

Thanks a bunch for your help.

[Sourrudedude]

Everyone else did a great job explaining the reasoning on necessary and sufficient. I just have one (hopefully) helpful hint. One of my problems is that even when I diagram something as A-->B I still feel the need to read it as a sentence in my head when I am looking at it. In this case I would read it as "A means B." It's just a simpler way for me to think about it than "If A is present then B must also be present."

[Chowfun]

Everyone else did a great job explaining the reasoning on necessary and sufficient. I just have one (hopefully) helpful hint. One of my problems is that even when I diagram something as A-->B I still feel the need to read it as a sentence in my head when I am looking at it. In this case I would read it as "A means B." It's just a simpler way for me to think about it than "If A is present then B must also be present."

Thanks

[gobosox]

This may be terrible advice, but I do a lot better when I brush through the answers quickly and eliminate 3 of them (usually) right off the bat. Then I focus on 2 that "seem" right and break them down a lot more.

Also, necessary is usually verbatim in the prompt, sufficient usually isn't. (Unless it's both, in which case it is usually a word for word connection, especially on the newer exams.)

[Chowfun]

I have exciting news! Thanks you all your advice, a little more buckling down, and help from a friend I am now able to tackle S&N. I did 22 questions and was able to get all of them correct. I understood why the correct answer was best and why the others were wrong. Granted it does take me longer than 1:45, but at least I am understanding and getting them correct. I think I will work on timing once I get through understanding all of LR. Although does anyone have advice on how to speed up? I guess that comes with practice, although that 1:45 time constant is pretty tough, I can't even see myself solving the problem in that timeframe.