Came across an interesting LG rule but not from a preptest Forum

[timmydoeslsat]

There is a logic game book I picked up just to look at and this rule made me think about whether this rule is biconditional. I initially saw this rule:

Slippers are always bought with the guide.

And went with:

S ---> G

However, I believe it is also true that:

G ---> S

I am guessing the reason I am stumped on this is the use of "always...with" in the rule.

Slippers are always bought with it.

So I know that if I have G, I must have S.

I also know that if I have S, I have G.

Is this rule biconditional or am I missing something?

[ggibelli]

There is a logic game book I picked up just to look at and this rule made me think about whether this rule is biconditional. I initially saw this rule:

Slippers are always bought with the guide.

And went with:

S ---> G

However, I believe it is also true that:

G ---> S

I am guessing the reason I am stumped on this is the use of "always...with" in the rule.

Slippers are always bought with it.

So I know that if I have G, I must have S.

I also know that if I have S, I have G.

Is this rule biconditional or am I missing something?

No this is not bi-conditional. All this is saying is that if you buy slippers it is absolutely certain you will have a guide. But just because you have a guide it doesn't require you to also have slippers. You could have a guide and a bike. Or a spoon. Or anything..

[KRog]

Here are the only things you can tell from this sort of conditional rule.
1. If you have G, then you have S.
2. If you don't have S, then you don't have G.

G ---> S

/S--->/G

To get the converse of the rule, flip it around AND negate BOTH sides. HTH

Edit: Corrected per convo below.

[marsdentromba]

I disagree with both posters above and believe the reason you haven't found this in an LSAT is because it's misleading and depends on your interpretation of the definition of 'with'.

You can easily interpret this, accurately, to mean "when you purchase G, you (must) also purchase S" Which is another way of saying that G is sufficient for S, G--> S.

The real issue is that the topic of the sentence is unclear, and could be taken to be either G or S. So it's not biconditional. It must be either G--> S or S--> G, but not both, and due to its construction it can be either.

To date, there are exactly 70 preptests with 280 logic games and well over 1000 rules to practice diagramming with. You neither need to nor should practice with unofficial games/rules.

Good luck!

[KRog]

Good call, marsdentromba.

Sorry OP, I originally skimmed the set up you provided and just saw that you needed help with negating the rule. But, as meardentromba has pointed out, it is very important to have the rule right in the first place! Sorry for any confusion. I have corrected my post above.