Conditional sequencing in LG- Accelerated Course book p. 37

[Stephanie Oswalt]

We received the following question from an Accelerated Course student. An instructor will respond below. Thanks!

I am reviewing page 37 of the Powerscore LSAT course book regarding conditional sequencing in logic games. While I can somewhat see how the either or, but not both diagrams were made, I'm not completely following the reason why. Could you please assist me in understanding the reasoning behind the example on page 37.

It says: Either R is taller than S, or else R is taller than T, but not both

the 2 correct diagrams are:

T-R-S or S-R-T

Is it like you are reversing each statement, then using the variable that is not used at the end? I'm pretty confused over here. Please help.

[Jonathan Evans]

Great question.

What's happening here is that we are extrapolating one step further from the initial symbolization.

Notice, given:

• Either R is taller than S, or else R is taller than T, but not both.

We can correctly infer the initial symbolization that "most students" do:

• R S
  OR
  R T

But we must add "but not both" to this symbolization because given that R S we know that R T.

Likewise, given that R T we know that R S.

What does this mean? What does R T mean? What does R S mean?

Consider each separately.

• R T means that R is not taller than T. What does this mean? It means T is taller than R. This can be symbolized as T R.
• R S means that R is not taller than S. What does this mean? It means S is taller than R. This can be symbolized as S R.

Now let's put it all together.

First scenario:

• R S and R T means R S and T R. Put the two together and we have T R S

Second scenario:

• R T and R S means R T and S R. Put the two together and we have S R T

Thus, this clue can be symbolized as:

• T R S
  OR
  S R T

I hope this helps!

[kashb]

Does this only apply to sequencing games?

[Luke Haqq]

Hi kashb!

In general, yes, the above discussion is focused specifically on an issue that arises in sequencing games, and a breakdown of the technique of how to approach diagramming it.

It's limited to sequencing games especially in the sense that language like "Either R is taller than S, or else R is taller than T, but not both" will almost certainly never be found in reading comprehension or logical reasoning. Rather, it's language you'd only find in the games section.

But remember that there can be hybrid games! For example, you might come across a grouping/sequencing game, one that involves both sequencing-type rules (such as R S T) and grouping-type conditional statements (such as A B C). In other words, on the question of whether this only applies to sequencing games, it's worth noting that you might encounter something like "Either R is taller than S, or else R is taller than T, but not both" on something that is primarily a grouping game. Since the statement is ultimately one about how to sequence variables, though, adding it to a grouping game would turn it into a hybrid game.