## When to write out the contrapositive in LG questions?

Prepare for the LSAT or discuss it with others in this forum.
crazi4law

Posts: 71
Joined: Sat Jul 16, 2011 9:21 am

### When to write out the contrapositive in LG questions?

I'm using the LGB right now, and it often stresses the importance of contrapositives in conditional statements. But in the answers, they don't always write all of the contrapositives out when setting up the question. So I was wondering, for which statements should I write out the contrapositive for?

Thanks!

giantwhale3798

Posts: 19
Joined: Thu Jun 14, 2012 7:56 pm

### Re: When to write out the contrapositive in LG questions?

The question seems to me a bit vague. I think whenever if/ not.. until/ unless appears, you need to write it down or at least be very aware of the existence of such relationship. Contrapositive relations is key to some assumption and inference questions.

Noblesse_Oblige

Posts: 44
Joined: Mon Feb 06, 2012 7:41 pm

### Re: When to write out the contrapositive in LG questions?

Always.

You should always write out the contrapositive.

Take this example:

A -> B
~A -> C

with just these you could be good to go, but it may take you longer. If you write out just the contrapositive of A - > B (~B -> ~A) Then you get ANOTHER conditional. ~B -> ~A -> C AND ~c -> A -> B

See, with just one contrapositive you now have 3 extra rules to help you finish the games faster.

And most questions won't ask, If A then what? They will ask if Not C then what. And look, you have the answer!

I find that most mistakes on the games are made when one doesn't write out all of the rules (contrapositives too) AND Make connections BEFORE you start answering questions.

If you do that, you will be faster and less likely to fall for LSAC's tricks.

GOOD LUCK!

Jeffort

Posts: 1888
Joined: Wed Jun 18, 2008 4:43 pm

### Re: When to write out the contrapositive in LG questions?

Noblesse_Oblige wrote:Always.

You should always write out the contrapositive.

Take this example:

A -> B
~A -> C

with just these you could be good to go, but it may take you longer. If you write out just the contrapositive of A - > B (~B -> ~A) Then you get ANOTHER conditional. ~B -> ~A -> C AND ~c -> A -> B

See, with just one contrapositive you now have 3 extra rules to help you finish the games faster.

And most questions won't ask, If A then what? They will ask if Not C then what. And look, you have the answer!

I find that most mistakes on the games are made when one doesn't write out all of the rules (contrapositives too) AND Make connections BEFORE you start answering questions.

If you do that, you will be faster and less likely to fall for LSAC's tricks.

GOOD LUCK!

Always! It takes less than a second or two. Simply write the cp slightly indented to the right under the original rule and write a bracket '(' on the left side of them as a visual cue so you know they go together. Simple and fast.

With that on the page you don't have to remember as much/rely on short term memory or spend more time doing the analysis again while applying the rules to the questions and answer choices or to easily find transitive connections when writing out your set-up and making deductions. You can then just simply glance at your list of diagrammed rules to apply them and do the relevant analysis to answer the questions.

( A B
..... ~B ~A

bdeebs

Posts: 128
Joined: Thu Mar 31, 2011 3:54 pm

### Re: When to write out the contrapositive in LG questions?

For me, the contrapositive always seemed like a natural implication of the original conditional that didn't need to be written out. After coming on these forums and seeing the general consensus that it should be written out, I tried it. I personally wasn't a fan. 1) I found myself using the original conditional even when the question called for the using the contrapositive (because I'm derpy like that). 2) When I was writing it out I would just think about how redundant it was, and that 2 second interruption in the flow of the game was enough to (albeit slightly) affect my mental state and productivity. 3) It took up more room and appeared cluttered, which made it harder for me to hold the rule set in my mind. I tried writing out the contrapositive for 6 games, decided it wasn't for me, and switched back.

That being said, I highly respect Jeffort's advice, and writing out the contrapositive will probably be beneficial for a majority of test takers. Not writing the contrapositive was just what I adopted for my personal plan of attack.

In the end, I think a good LG strategy should be individually tailored for the way each person thinks. I would conform to the metagame initially, but if something doesn't jive with the way your brain works as well as something else might (and you can articulate why the other approach could be better), experiment with it a little.

cc.celina

Posts: 602
Joined: Fri May 25, 2012 1:17 pm

### Re: When to write out the contrapositive in LG questions?

Just to add to the voices, I always write contrapositive for in/out games that have a crapload of conditional rules. It just makes it easier to make inferences. Before starting the game I do a quick scan for any elements that are repeated and write out new rules if I can (i.e. if I have C->~A and somewhere else I have ~A->B, then I write C->B)

If its like an ordering game or something and it's the only conditional rule I don't write it. (ex: if A is seventh, B is first. I write A7->B1 but don't bother writing the contrapos because it just doesn't seem necessary)

For super complicated conditionals (If F is before G, then H is next to I) I don't write the contrapos because personally it seems like a waste of time.

What bdeebs said, basically. There's no rule. If always writing it works for ya, then always write it. As I improved I found that I needed to write them out less often. That may or may not be the way to go. If you find yourself missing q's/being really slow on games where you didn't write out all the contra's, probs better to write them. Good luck!