Reply To: PT 59 Game 3

March 23, 2016 at 10:45 am #1618
LSAT Dan
Participant

When you translate conditional rules in a logic game, always add the contrapositive to your checklist.  The first rule is:

~R –> J

The second rule is:

M –> ~J

But if you take the contrapositive of the second rule, it’s:

J –> ~M

Now you have J in the same state (not-negated) as the necessary term in one rule (~R –> J) and the sufficient term in another (J –> ~M).  So the connection (~R –> J –> ~M) is direct.  The essence of combined rules is being able to use the same term as the sufficient term in one rule and the necessary in another.  Writing out the contrapositive of all of your rules maximizes the chances that you’ll be able to do that.  It basically provides more possible triggers.  Assuming that you correctly untangled the rules and diagrammed them correctly, that’s pretty much all it comes down to.

Personally, I don’t consider this a key inference.  I find that for most students, combining conditional rules (particularly in in-&-out games) adds more confusion and takes more time than it’s worth.  I think that a concise, accurate checklist of individual rules (and their contrapostives) is the better way to go.  However, I’m certainly in the minority among LSAT tutors/writers with that view.  On the other hand, I *do* believe that combining rules in sequencing games is very helpful, because of the additional visual cues (stuff on the left happened before stuff on the right) that it provides.  Just my 2 cents.