LRB Page 162, Conditional Reasoning Diagramming Drill 8 + 9

[Dave Killoran]

This post is in response to the following question:

Hello,
I recently purchased the LSAT Bible Trilogy (Logic Games Bible, Logical Reasoning Bible, and Reading Comprehension Bible). I am currently on Chapter 6 of the Logical Reasoning Bible and I am doing the Conditional Reasoning Diagramming Drill on page 162. I am getting the answer correct (I think), but in a different order, and wanted to verify with someone from powerscore that I was attacking the diagram correctly, specifically on number 8 and 9 on page 162.

8). A computer cannot operate without an operating system.
I chose operating system as the Necessary Condition and computer cannot operate as sufficient. I then diagrammed as below: X= None CO = Computer Operation OS = Operating System

XCO --> XOS

The computer cannot operate without an operating system

Contrapostive:

OS --> CO

If the computer has an operating system, then it can operate

However, the answers on page 166 diagram it as below:

CO --> OS
XOS --> XCO

So, I am wondering if during my analytical process I am mixing them up, or if my process is leading me to the correct answer, just in a different order.

I did the same thing on number 9. WH --> AC and XAC --> XWH

Making achieving success the necessary condition and working hard the sufficient condition.

Thanks so much for your help. And thank you for the amazing resources. Truly, I have only started on the Logical Reasoning Bible, but I cannot be more happy with my purchase and its usefulness.

Ok, thanks for the questions! Let’s take a look at both items you asked about.

Drill #8. There’s a problem with your diagram in this one, and I think you missed one of the conditional indicators. In the sentence in the drill, you might note the keyword “without.” Over on page 160 I discuss the Unless Equation, which applies to "without." So, what follows "without" is the necessary condition (operating system) and you negate the remaining term (which then becomes "computer operates"). That leads to the following diagram, which is the same as the diagram in the book:


CO OS


Please take a look at that, and let me know if it makes sense.


Drill #9. In some ways, this is the trickier question of the two. In the drill answer key I explain a bit about how "only way" works, and it' definitely is challenging. Let's look at this one in more detail.

The word "only" in this problem introduces a necessary condition. But, what does "only" actually modify (this is the key to understanding this diagram)? In this case, "only" modifies "way," and "way" refers to "work hard" Thus, work hard" is the necessary condition, and the remainder ("achieve success") is the sufficient condition. This leads to the diagram you see in the book:


AS WH


Consider this parallel example:


The only way to the top of the mountain is the switchback trail


"Way" modifies "trail," and thus the diagram is:


Top of mountain switchback trail


So, if you see someone on top of the mountain, then according to the author they took the switchback trail. On the other hand, if someone took the switchback trail, does that mean they got to the top of the mountain? No, so switchback trail is not a sufficient condition.

So, just because "only" is close to a condition doesn't mean it is actually attached to that condition; you need to make sure that it actually refers to that condition (and this is one example where it doesn't refer to the closest condition).

On pages 184-185 I talk in greater detail about "only way" and "the only," which are alternate ways to look at this sentence (the idea being that there is sometimes more than one way to interpret a sentence, but, like climbing a mountain, they all arrive at the same place). Please take a look at those pages and let me know if they help.

Thanks!