Critical Reasoning Question Types-Assumption questions

An assumption bridges the gap between an argument’s evidence and conclusion.  It’s a piece of support that isn’t explicitly stated, but that is required for the conclusion to remain valid.  When a question asks you to find an author’s assumption, it’s asking you to find the statement without which the argument falls apart

Denial Test

To test whether a statement is necessarily assumed by an author, we can employ the Denial Test.  Here’s how it works:  Simply deny or negate the statement and see if the argument falls apart.  If it does, that choice is a necessary assumption.  If, on the other hand, the argument is unaffected, the choice is wrong.  Consider this simple stimulus:

Allyson plays volleyball for Central High School.

Therefore, Allyson must be over 6 feet tall.

You should recognize the second sentence as the conclusion and the first sentence as the evidence for it.  But is the argument complete?  Obviously not.  The piece that’s missing-the unstated link between the evidence and conclusion-is the assumption, and you could probably prephrase this one pretty easily:

All volleyball players for Central High School are over 6 feet tall.

Is this an assumption really necessary to the argument?  Let’s negate it using the Denial Test.  What if it’s not true that all volleyball players for Central High are taller than 6 feet?  Can we still logically conclude that Allyson must be taller than 6 feet?  No, we can’t.  Sure, she might be, but she also might not be.  By denying the statement, then, the argument falls to pieces; it is no longer valid.  And that’s our conclusive proof that the statement above is a necessary assumption of this argument.

So, we can use the Denial Test to chick whether a statement is an assumption, but what if we haven’t a clue about what the assumption is?  Is there a way to track it down?  Sure enough, there is?

Compare the ideas in the evidence with those in the conclusion.  If the conclusion has an idea (an important word) but the evidence does not, then you’ve found an assumption.  A new idea cannot occur in the conclusion, so there must be an assumption about this idea.  Every idea in the conclusion need support-that is, evidence.  While it may not be quite clear what the assumption is, knowing something about it allows us to prephrase and eliminate choices.

As we’ve just seen, you can often prephrase the answer to an Assumption question.  By previewing the question stem, you’ll know what to look for.  And stimuli for Assumption questions just “feel” as if they’re missing something.  Often, the answer will jump out at you, as it did here.  But in more difficult Assumption questions, it might not be so obvious.  Either way, use the Denial Test to quickly check whichever choice seems correct.

Sample Question Stems

Assumption questions are worded in some of the following ways:

• Which one of the following is assumed by the author?
• Upon which one of the following assumptions does the author rely?
• The argument depends on the assumption that?
• Which of the following, if added to the passage, will make the conclusion logical?
• The validity of the argument depends on which one of the following?
• The argument presupposes which one of the following?