LSAT 138 | Section 4 | Logical Reasoning: Q17

LR Question 17 Explanation

QUESTION TEXT: Humankind would not have survived, as it clearly has…

QUESTION TYPE: Parallel Reasoning

CONCLUSION: Humanity’s ancestors were at least somewhat altruistic.

REASONING: Humanity survived because early humans were ready to sacrifice themselves to protect their kids and relatives. This sacrifice can be viewed as altruism. And humanity has survived.

ANALYSIS: This is a good argument. It has the following structure.

• Humans survive ➞ ready to sacrifice ➞ form of altruism.
• Humanity did survive. So early humans had a form of altruism.

I’ll admit that I didn’t have this exact structure until after I looked at the argument. But I had a rough idea and the right answer stood out for me. I’m presenting the exact structure so you can learn from it – but know that you don’t need to have a precise understanding to see that the other answers are missing something.

One important element in the stimulus: “as it clearly has [survived]”. This isn’t a conditional statement. Instead, it’s a statement of fact showing that a condition occurred. It’s like saying “cats have tails. And this animal is a cat”. The second statement is a fact that lets us draw the conclusion “this animal must have a tail”.

It turns out that all of the wrong answers are bad arguments! That’s another way to eliminate them, apart from structure. If the stimulus presents a good argument, then the right answer must also be a good argument.

___________

1. CORRECT. This matches.
    
   Grades ➞ Studying ➞ Time management
   Some students raised grades. So some students study.
2. This is a flawed argument, it makes an incorrect negation.
    
   Reasoning: Consume ➞ manufacture
   Conclusion: Consume ➞ manufacture
3. This is a bad argument. There might be some other way to protect the ecosystems, other than government action.
4. This is a bad argument. The argument didn’t say how the power for the replacements will be supplied. Maybe it will be supplied from renewable sources such as solar.
5. This is a bad argument. Here’s the structure:
    
   Reasoning: Well designed ➞ harmonize
   Harmonize ➞ well designed ➞ expensive
    
   Conclusion: Harmonize xor expensive
    
   This answer says “or else”. That phrasing refers to the exclusive or: “one or the other, but not both”. The way to draw this logically is with the “xor” symbol.
    
   The reason the argument is bad is that you could have a building that is expensive and also doesn’t harmonize. You can have the necessary condition (“expensive”) while also lacking the sufficient condition (“harmonize”). So this isn’t a xor relationship (“one or the other or not both”): you could instead have neither!