Sufficient & Necessary Questions - - Question 1

People who are red/green color-blind cannot distinguish between green and brown. Gerald cannot distinguish between gr...

MARIO October 25, 2013

Argument Completion Drill

I understand my post does not pertain to this specific question. However, there was not a place to post under the drills section. In the argument completion drills section there is a drill that contains a setup like the following: A-B B-C A does not exist I understand by implementing the contrapositive of the first principle we arrive at an impossible argument. However, by simply eliminating the sufficient condition of A, how does that guarantee that B does not exist? If being a lawyer requires one to go to law school, how does saying one is not a lawyer sufficient in concluding they have not attended law school?

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Naz October 27, 2013

In this drill we are given two principle rules:

(1) A ==> B
Contrapositive: not B ==> not A

(2) B==> C
Contrapositive: not C ==> not B

We are also presented with the premise: "A does not exist." The variable "not A" (a.k.a. A does not exist) is not the sufficient condition for any of the principle rules or their contrapositives.

Therefore, "not A" does not lead us to any other information, and so we cannot properly infer something from all the information given us. That is why the correct conclusion is: "No Valid Conclusion." This does not mean that "B does not exist." It merely means that we cannot conclude anything else with 100% certainty.

Hope that was helpful! Let me know if you have any other questions.

patpiff August 19, 2017

Also in re to the argument completion drill:

For some reason, when I click on the drill, I receive a prompt to download the s&n portion of the course. Even after downloading it again, it doesn't work. Please advise! Thanks!

vkaszu September 26, 2017

I also have this problem with the drills not downloading

Mehran September 26, 2017

@patpiff @vkaszu please delete the app and reinstall.

This will resolve this issue. Sorry for the inconvenience.