Question about contrapositives and splitting compound conditionals.

JCDante
Posts: 43
Joined: Mon Dec 15, 2014 11:24 pm

Question about contrapositives and splitting compound conditionals.

Postby JCDante » Tue Jun 09, 2015 5:35 am

Going through the Trainer: just got a couple questions.

1.) Why does "or" turn into "and" when you reverse and negate during a contrapositive (and vice versa)? I understand that this is a method to take advantage of, but I do no understand the abstract reasoning behind it.

2.) If I understand correctly, when you have a trigger with "and", you cannot split it up, correct?

For example: If not H ----> J or L
If not J & not L ----> H

This cannot be split because if not J & not L are tied together. But say this was:

If not J or not L ----> H

then it could be split into

Not J ----> H
Not L ----> H

DrYamata
Posts: 6
Joined: Mon Jun 08, 2015 11:14 pm

Re: Question about contrapositives and splitting compound conditionals.

Postby DrYamata » Tue Jun 09, 2015 2:23 pm

JCDante wrote:Going through the Trainer: just got a couple questions.

1.) Why does "or" turn into "and" when you reverse and negate during a contrapositive (and vice versa)? I understand that this is a method to take advantage of, but I do no understand the abstract reasoning behind it.

2.) If I understand correctly, when you have a trigger with "and", you cannot split it up, correct?

For example: If not H ----> J or L
If not J & not L ----> H

This cannot be split because if not J & not L are tied together. But say this was:

If not J or not L ----> H

then it could be split into

Not J ----> H
Not L ----> H


Just think about it in concrete terms real quick.. it always helps to bring logic down to the real world to understand it.. just make sure to be able to take it back up into abstraction :-)

1. If I said "There are apples or oranges." It means there is either fruit, or both fruits (unless it's an exclusive or.) To say that it is not the case that there are apples, oranges, or both, you have to say "not apples AND not oranges" which is logically equivalent to "not (apples or oranges)" I suggest just drilling the hell out of demorgan's laws.. just memorize it. It's only a few logical operators and you need to be able to whip it out on test day.

2. Correct. "AND" sufficient conditions must occur together in order to trigger the necessary.

JCDante
Posts: 43
Joined: Mon Dec 15, 2014 11:24 pm

Re: Question about contrapositives and splitting compound conditionals.

Postby JCDante » Tue Jun 09, 2015 7:13 pm

Thank you so much! That example really cleared things up for me.




Return to “LSAT Prep and Discussion Forum”

Who is online

Users browsing this forum: connordalto, potatocowpower and 7 guests