# Law School Discussion

Nine Years of Discussion
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### AuthorTopic: Necessity vs. Sufficiency  (Read 6191 times)

#### freakoutgirl

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• Posts: 77
##### Necessity vs. Sufficiency
« on: November 20, 2006, 02:24:50 PM »
I am still confused on what Kaplan means by this whole "necessity vs. sufficiency" idea behind flaw questions.  Can someone explain this, using examples, in very simple terms?

Also, can someone give a run down of the wrong answer choices most frequently used by lsat?

Thanks, I love this FORUM! I finally have friends to "freak out"/obsess about the LSAT with...

P.S.S.- who's going to be spending their family Thanksgiving studying for the LSAT? Don't you just love it! not!
Major: Psychology & Political Science
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#### guyminuslife

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• Posts: 657
• Fascism -- @#!* Yeah!
##### Re: Necessity vs. Sufficiency
« Reply #1 on: November 20, 2006, 02:40:43 PM »
I don't know Kaplan, but it's pretty obvious that the plain difference between the two terms is:

sufficiency - if X, then Y is possible
necessity - only if X, then Y is possible

So for instance:

sufficiency--
If I have a Ferrari, I can drive around
(but I could do it with a Volksawagon, too)

necessity--
Only if I have a Ferrari, I can get from 0 to 60 in 8 seconds
(I couldn't do it with a Volkswagon or any other kind of car)

#### LSATnooblet

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• Posts: 91
##### Re: Necessity vs. Sufficiency
« Reply #2 on: November 20, 2006, 02:43:05 PM »
If you are a cat, you have hair. Sufficient = cat, Necessary = hair.

If then statements can be broken down in to suff. and necc. or in other words into formal logic. However, don't get such conditional statements confused with cause and effect statements. One way of putting it is that the sufficient is what results from the necessary and is not essential to the arguement. Someone could probably explain this better than I can but I took a shot anyways.

As for the most common wrong answers for LR questions at least, I would have to say those would be answer choices that have subjective or extreme wording that go beyond the logical scope of the stimulus. Focus on words like some, most, all etc when picking your answers. This alone will eliminate a truckload of answers.

#### theo

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• Posts: 1834
##### Re: Necessity vs. Sufficiency
« Reply #3 on: November 20, 2006, 02:59:20 PM »
I don't know Kaplan, but it's pretty obvious that the plain difference between the two terms is:

sufficiency - if X, then Y is possible
necessity - if and only if X, then Y is possible

So for instance:

sufficiency--
If I have a Ferrari, I can drive around
(but I could do it with a Volksawagon, too)

necessity--
If and only if I have a Ferrari, I can get from 0 to 60 in 8 seconds
(I couldn't do it with a Volkswagon or any other kind of car)

This is completely, abjectly WRONG.

It's like watching a hideous, lethal highway wreck.

quid leges sine moribus vanae proficiunt?

#### guyminuslife

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• Posts: 657
• Fascism -- @#!* Yeah!
##### Re: Necessity vs. Sufficiency
« Reply #4 on: November 20, 2006, 03:06:50 PM »
I don't know Kaplan, but it's pretty obvious that the plain difference between the two terms is:

sufficiency - if X, then Y is possible
necessity - if and only if X, then Y is possible

So for instance:

sufficiency--
If I have a Ferrari, I can drive around
(but I could do it with a Volksawagon, too)

necessity--
If and only if I have a Ferrari, I can get from 0 to 60 in 8 seconds
(I couldn't do it with a Volkswagon or any other kind of car)

This is completely, abjectly WRONG.

It's like watching a hideous, lethal highway wreck.

How so? Again, I am not familiar with Kaplan's specific use of the terms.

If a particular condition is sufficient for another condition to occur, then the implication is that it's not necessarily the only condition under which the second condition can occur. But it works.

If it is necessary, then it is an absolute prerequisite. Granted, there may be other prerequisites. Perhaps it should be changed to "only if X, then Y is possible." This edit has been made. I would not, however, characterize the description as "abjectly" wrong, as it has been corrected by a minor edit.

Perhaps you are thinking that sufficiency = meeting all necessary conditions. Which is true. But the example still stands.

It may be possible that Kaplan refers to this type of question as the difference between

If X, then Y, and
If X, then Y is possible

Which admittedly does correlate with the kind of questions asked on the LSAT. But like I said, I'm not familiar with the particular Kaplan definition, and their LSAT prep sucks anyway, so I merely used the plainspoken definition.

#### imwithhappy

• Sr. Citizen
• Posts: 182
##### Re: Necessity vs. Sufficiency
« Reply #5 on: November 20, 2006, 03:42:59 PM »
This is how I figured it out and it works for me.

Sufficient: What you get (result)
Necessary: What you did/do  (action)

This doesn't work in every case, but it helped me.
University of Oklahoma '11

#### theo

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• Posts: 1834
##### Re: Necessity vs. Sufficiency
« Reply #6 on: November 20, 2006, 03:53:59 PM »
This is how I figured it out and it works for me.

Sufficient: What you get (result)
Necessary: What you did/do  (action)

This doesn't work in every case, but it helped me.

This one is even worse.
quid leges sine moribus vanae proficiunt?

#### rosey

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• Posts: 65
##### Re: Necessity vs. Sufficiency
« Reply #7 on: November 20, 2006, 04:00:40 PM »
If something is sufficient, then it alone will get the job done. It doesn't have to be the ONLY thing that is able to get the job done, but it alone works. For example, If X then Y. X is the sufficient term. If you have X, then that alone is enough to bring about Y. Other things, maybe Z, might bring about Y, but you know, for sure, that X is enough (is SUFFICIENT) to bring about Y.

If something is necessary, then it is needed to bring about the other, but not enough, it is not the ONLY thing required. Using the same simple example, in If X then Y, the Y term in the necessary term. It is necessary to have Y to have X, but having Y alone is not enough to ensure that you have X.

Make sense?

As for the Kaplan classic wrong answer types: 180; distortion; 1/2 right,1/2 wrong; out of scope; ... hm, can't think of any others...

Good luck!
Penn Law 2010!

#### JellyBelly

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• Posts: 92
• should I wear RED or PLAID??????????????????
##### Re: Necessity vs. Sufficiency
« Reply #8 on: November 20, 2006, 04:05:24 PM »
is this okay?

sufficient:
if i boil an egg, i can make egg salad.

neccesary:

if i made egg sald, then i boiled an egg?

#### theo

• Sr. Citizen
• Posts: 1834
##### Re: Necessity vs. Sufficiency
« Reply #9 on: November 20, 2006, 04:13:02 PM »
is this okay?

sufficient:
if i boil an egg, i can make egg salad.

neccesary:

if i made egg sald, then i boiled an egg?

NO
quid leges sine moribus vanae proficiunt?