October 2011 LSAT Section 4 Question 19

It can be inferred that the author of passage B would regard which one of the following as a mistaken assumption unde...

NK848 on April 25, 2020

Diagramming question

As I understand, passage A is saying that interest in replicating the genes promotes altruistic behavior, thus IRG "explains" AB. IRG ==>AB B is criticizing that all sorts of interests would explain any given behavior, and "[w]hat is needed to make it decisive that a particular interest explains a particular behavior is that the behavior would be reasonable only if one had that interest". So B seems to be saying that it should be: AB ==> IRG My question is: can words/phrases like "A explains B," "A decisively explains B," and " B is caused by A" diagrammed?

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SamA on May 5, 2020

Hello @NK848,

I would refrain from using sufficient and necessary diagrams for passage A. Having said that, it is perfectly fine if you want to make a note to remind yourself of the relationship between replicating genes and altruistic behavior. I just want you to understand that this is not a sufficient/necessary relationship.

Your diagram, IRG ==> AB, states that interest in replicating genes guarantees altruistic behavior. Every time there is such an interest, altruistic behavior follows. This is too strong for what the passage says. Author A is simply proposing a theory to explain altruistic behavior.

Very rarely will I make sufficient and necessary diagrams on the reading comprehension section, but Passage B might be an exception. Your understanding of Author B's argument makes sense. She is saying we can only conclude that interest in replicating genes is the cause of altruism only if:

AB ---> IRG

However, the author argues that this is not the case. Therefore, we cannot conclude that interest in replicating genes causes altruism. Maybe altruism exists for its own sake.

In short, I would not use sufficient and necessary diagrams for "A explains B" or "B is caused by A." Look for your standard sufficient and necessary indicators like "only" or "always."

If your example said, "B is only caused by A," I would write B ---> A.
or
"A always causes B." A ---> B

NK848 on May 7, 2020

Thank you! I was trapped by the "only if" but your explanation makes sense.