Formal logic

[Johnclem]

Hi
I am having trouble with formal logic. I tried following the bible but still got lost.
Here's another one I seem to be having trouble with.
Chapter 13 :

1) M<-some->N<-------->O

Step one : start from M and follow the train leads me to inference M some O which is so far cool !
But here comes the trouble. Since some statements could be read in both directions.. ( M some O OR O some M ) doesn't the inference then violate the rule of not combining some statements ?

Super confusing and so far I ain't a big fan f conditional logic !

John

[Nikki Siclunov]

Hey John,

The prohibition against making an inference involving two "some" relationships only applies if there are, indeed, two different "some" relationships that you're crossing over. The mere fact that a "some" relationship can be read both ways does not mean that you're drawing an inference based on the combination of two different "some" relationships: if that were the case, you'd never be able to make any inference from a chain in which a "some" relationship is present.

Check out my answer to your other question about the Some Train, which is directly relevant to your question here.

One last thing to keep in mind: the vast majority of recent LSAT's have absolutely no Formal Logic questions in them; some may have 1, at most 2. It's only worth spending the time to master Formal Logic if you're crystal clear on all other concepts being tested, and your scores are solidly in the top-1%. If this is not the case, there are bigger fish to fry than Formal Logic

Thanks,

[Dave Killoran]

Hi John,

Let me add one point to Nikki's spot-on comments, and that is that once you build an inference bridge, it exists, and you can then cross it both ways (although, to be fair, when you go "backwards" across the bridge you may have a lesser relationship; that doesn't occur here because "some" is reversible). so, once we had M O, that was established as fact, and we are allowed to go "back" across that inference bridge, which allows us to infer O M.

The other thing about Formal Logic is that once it clicks, all this will look straightforward in retrospect. It's hard at first, but it gets easier once you absorb how this all works. I've seen it before many times

Thanks and good luck!