Logical reasoning (Assumption Family Questions)

[AbhistD667]

Hello everyone! I am preparing for LSAT from the Manhattan prep books and have recently finished assumption family chapters. Can someone tell me what should I do in these questions when I can't find the gap between the premise and the conclusion?

[Laura Damone]

Hi there!

First thing to do is look for the "new kid" in the conclusion and the "orphan" in the premises. By that I mean, a concept in the conclusion that wasn't addressed in the premises, and a concept from the premises that didn't carry through to the conclusion. Consider an argument with this structure:

Premise: Deforestation is reducing the number of species in the rain forest.
Conclusion: Industrial agriculture is having a negative impact on biodiversity.

Who's the new kid in the conclusion? "Industrial agriculture." The premise doesn't address this concept at all. Now, you might be thinking "the premise doesn't use the term 'biodiversity' either" and you'd be right, it doesn't use that term. But the premise does address the concept of biodiversity when it talks about the reduction of the number of species. Biodiversity is the number of species, so even though the terms are different, the concept is the same.

So, who's the orphan in the premises? "Deforestation." It's mentioned in the premises but it doesn't carry through to the conclusion.

The gap in reasoning, at the most basic level, can be articulated by saying "the premises talk about deforestation (the orphan) but the conclusion is about industrial agriculture (the new kid)."

Now, sometimes you won't be able to spot a new kid or an orphan. Occasionally, LSAT arguments in Assumption Family questions will appear to be valid. When this happens, it usually means that the assumption is really subtle. In these cases, the gap may be best articulated as an objection to the argument, so try to read like a debater and say "OK LSAT author, I accept your premises, but I don't think they guarantee your conclusion because .... " Fill in that blank with your objection.

If neither of these approaches reveal the gap, and that will happen sometimes, you'll have to use the answer choices to drive your understanding. Every so often I'll come out of an Assumption family stimulus, typically Necessary Assumption, Strengthen or Weaken, thinking "Huh...that seems like a solid argument" even after digging into the core and reading like a debater. No need to panic. I'll read each answer and carefully consider whether it addresses a gap I missed, and in most cases, it's a face-palm moment and I'll see that I was tricked by a subtle conceptual shift or failed to notice some totally reasonable objection.

Hope this helps!