Necessary Q's, I have a question? Forum

[Jimlaw123]

Hello to all,

Good luck on the LSAT those studying. The last time I took the LSAT the questions that killed me were "Necessary" and "Sufficient" questions.

I have a thought process about these now that i"m looking over them, but I need some advice, to know if my reasoning is off. Should I be looking at the Necessary questions as "Something before the argument to make it valid"? In a sense, should I just be looking for answer choices that make the outcome possible to "Must happen".

For instance, let's say, "Tom and Jesse drove to the store, Tom went and bought chips, Jesse bought beer, then they got drunk", and the answer should be something along the lines of, "Tom and Jessy needed the car keys to the store", in actuality they had to have the "car keys, to drive, then go to the store" is my reasoning. Should it be something that is "Before the argument" to make it valid?

Also on Sufficient, it's just what is "Enough needed to make the statements true", so in the answer choices only one will be "enough" to make the answer choices true? To all those who read this thanks. I really need some clarity on these as these are the ones that killed me the last time, trying to get a jump on it this time. Thanks again.

(And If I'm completely off, please just explain the best method you've come up with for "Necessary and Sufficient" questions, thanks.)

[mornincounselor]

Post removed.

[lymenheimer]

A necessary (or required) assumption is something that must absolutely 100% positively be true in order for the argument to ever possibly be true. It doesn't have to get us very far to proving our argument, but if it were not true the argument could never be true. If my argument was "I will be the greatest President of the United States ever" then a required assumption could be

(a) I will live longer than my 35th birthday.
(b) I was born in the United States.
(c) I am willing to work in the public sector.

Now even if all 3 of these things are true, it is still monumentally unlikely I will ever prove my argument, but if any one of these items are not true then it is IMPOSSIBLE for me to prove my argument.

A sufficient assumption is something that, on it's own, proves my argument. If we use the same argument as above, there can be no assumption sufficient to prove the argument. So practically speaking if the question is going to ask us for a sufficient assumption the test writers are pretty limited as to what they can ask. The argument has to be reasonable enough for a single assumption to prove the argument. Sufficient assumption questions often involve connecting two pieces of an argument together. Here's an example:

Premise:All dogs have four legs.
Premise:All animals with four feet have at least ten toes.
Conclusion: This dog has at least ten toes.

A sufficient assumption is that "If an animal has four legs then it has four feet."

FTFY

[CardozoLaw09]

A necessary (or required) assumption is something that must absolutely 100% positively be true in order for the argument to ever possibly be true. It doesn't have to get us very far to proving our argument, but if it were not true the argument could never be true. If my argument was "I will be the greatest President of the United States ever" then a required assumption could be

(a) I will live longer than my 35th birthday.
(b) I was born in the United States.
(c) I am willing to work in the public sector.

Now even if all 3 of these things are true, it is still monumentally unlikely I will ever prove my argument, but if any one of these items are not true then it is IMPOSSIBLE for me to prove my argument.

A sufficient assumption is something that, on it's own, proves my argument. If we use the same argument as above, there can be no assumption sufficient to prove the argument. So practically speaking if the question is going to ask us for a sufficient assumption the test writers are pretty limited as to what they can ask. The argument has to be reasonable enough for a single assumption to prove the argument. Sufficient assumption questions often involve connecting two pieces of an argument together. Here's an example:

Premise:All dogs have four legs.
Premise:All animals with four feet have at least ten toes.
Conclusion: This dog has at least ten toes.

A sufficient assumption is that "If an animal has four legs then it has four feet."

FTFY

i think his point was that he has to live past 21 to make it to 35

[lymenheimer]

i think his point was that he has to live past 21 to make it to 35

But that's also assuming he doesn't die in between 21 and 35. Also assuming that when he turns 35 it will be during an election season to where he can immediately be elected. Also assuming that the greatness achieved will be in the years during his tenure when he is alive. This is exactly something the LSAT would get you on. Gotta be prepared for ANYTHING!!!

[ihenry]

i think his point was that he has to live past 21 to make it to 35

But that's also assuming he doesn't die in between 21 and 35. Also assuming that when he turns 35 it will be during an election season to where he can immediately be elected. Also assuming that the greatness achieved will be in the years during his tenure when he is alive. This is exactly something the LSAT would get you on. Gotta be prepared for ANYTHING!!!

He was talking about necessary assumptions, and being older than 21 is a perfectly legitimate necessary assumption -- you may also say someone must be older than 3 to be the president, and that is NECESSARY. All conditions you came up may be false and the person may not be the president of America, but that does not affect the fact that being over 3 year old is NECESSARY for someone to be the president.

[CardozoLaw09]

i think his point was that he has to live past 21 to make it to 35

But that's also assuming he doesn't die in between 21 and 35. Also assuming that when he turns 35 it will be during an election season to where he can immediately be elected. Also assuming that the greatness achieved will be in the years during his tenure when he is alive. This is exactly something the LSAT would get you on. Gotta be prepared for ANYTHING!!!

He was talking about necessary assumptions, and being older than 21 is a perfectly legitimate necessary assumption -- you may also say someone must be older than 3 to be the president, and that is NECESSARY. All conditions you came up may be false and the person may not be the president of America, but that does not affect the fact that being over 3 year old is NECESSARY for someone to be the president.

exactly