Question about the structure behind necessary assumptions

echoplasm
Posts: 14
Joined: Wed Dec 04, 2013 12:41 pm

Question about the structure behind necessary assumptions

Postby echoplasm » Fri Feb 20, 2015 12:30 pm

In all the sources I've read, they diagram necessary assumptions as:

Conclusion --> Necessary assumption

But then I'm confused as to why necessary assumptions are referred to as "unstated premises," if premises are supposed to be sufficient conditions, not necessary conditions. For example, take this argument:

1. Socrates is a human.
2._____
Therefore, Socrates is mortal.

The unstated premise here is all humans are mortal. However, we would then diagram this on an necessary assumption question as:

If Socrates is mortal --> All humans are mortal.

How does this make sense? Or are you not supposed to view the original argument as this way?

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rnoodles
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Joined: Sat Feb 07, 2015 5:52 pm

Re: Question about the structure behind necessary assumptions

Postby rnoodles » Fri Feb 20, 2015 12:49 pm

echoplasm wrote:In all the sources I've read, they diagram necessary assumptions as:

Conclusion --> Necessary assumption

But then I'm confused as to why necessary assumptions are referred to as "unstated premises," if premises are supposed to be sufficient conditions, not necessary conditions. For example, take this argument:

1. Socrates is a human.
2._____
Therefore, Socrates is mortal.

The unstated premise here is all humans are mortal. However, we would then diagram this on an necessary assumption question as:

If Socrates is mortal --> All humans are mortal.

How does this make sense? Or are you not supposed to view the original argument as this way?


Try changing everything back into "if...then" statements, which could help if you don't recognize "all" (and other terms) function similarly to "if" and others ("only if," for example) function similarly to "then." That's why "All humans are mortal." would be diagrammed as follows: Humans --> Mortal.

If all humans are mortal, and Socrates is in fact a human, then the conclusion follows that Socrates is also mortal. Try checking out the Powerscore LR Bible. It really explains this concept quite well. The Trainer also helped clear up questions I had with Powerscore's methods.

echoplasm
Posts: 14
Joined: Wed Dec 04, 2013 12:41 pm

Re: Question about the structure behind necessary assumptions

Postby echoplasm » Fri Feb 20, 2015 1:10 pm

The LR Bible is one of the sources I'm using. What I don't understand is why we're allowed to diagram:

Conclusion --> Premise

Because aren't premises supposed to be sufficient conditions in general? So for necessary assumption questions, the assumption is still a premise. In that case, the argument shouldn't make sense if we diagram it as Conclusion --> Assumption, yet it does.

peke
Posts: 46
Joined: Sat May 25, 2013 6:01 pm

Re: Question about the structure behind necessary assumptions

Postby peke » Fri Feb 20, 2015 8:21 pm

The necessary premise by definition if missing, the conclusion falls apart. So probably a more intuitive way of diagramming is

!(necessary assumption) -> !(conclusion)

On the other hand a sufficient premise allows us to draw the conclusion, again by definition.

(sufficient assumption) -> conclusion




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