Determining an argument’s necessary assumption, as we’ve just seen, is required to answer and Assumption question. But it also is required to answer another common type of question: Strengthen or Weaken the argument.
One way to weaken an argument is to break down a central piece of evidence. Another way is to attack the validity of any assumptions the author has made. The answer to many Weaken the Argument questions is the one that reveals an author’s assumption to be unreasonable; conversely, the answer to many Strengthen the Argument questions provides additional support by affirming the truth of an assumption or by presenting more persuasive evidence.
Let’s use the same stimulus as before but in the context of these other question types:
Allyson plays volleyball for Central High School
Therefore, Allyson must be over 6 feet tall.
Remember the assumption holding this argument together? It was that all volleyball players for Central High are over 6 feet tall. That’s the assumption that makes or breaks the argument. So, if you’re asked to weaken the argument, you’d want to attack that assumption:
Which one of the following, if true, would most weaken the argument?
Answer: Not all volleyball players at Central High School are over 6 feet tall.
We’ve called into doubt the author’s basic assumption, thus damaging the argument. But what about strengthening the argument? Again, the key is the necessary assumption:
Which one of the following, if true, would most strengthen the argument?
Answer: All volleyball players at Central High School are over 6 feet tall.
Here, by confirming the author’s assumption, we’ve in effect bolstered the argument.