QUESTION TEXT: Rhonda will see the movie tomorrow afternoon…
QUESTION TYPE: Parallel Reasoning
CONCLUSION: Rhonda won’t see the movie.
REASONING: Ted won’t go to the concert. That means that Paul won’t go to the concert. And Rhonda will only go to the movie if Paul goes to the concert.
ANALYSIS: This is a good argument. It joins two sufficient-necessary statements and reasons using the contrapositive:
Rhonda movie ➞ Ted concert ➞ Paul concert
Paul doesn’t go ➞ Ted doesn’t go ➞ Rhonda doesn’t go
___________
- This is a bad argument. Finding a babysitter was a necessary condition for Janice visiting but it wasn’t a sufficient condition.
- CORRECT. This is a good argument. Gary does laundry ➞ peter has to work ➞ Cathy ill. Since Cathy isn’t ill, we can use the contrapositive to show that Gary won’t do laundry.
- This is a bad argument. The market having trout was a sufficient condition for barbecuing fish, but not a necessary condition. Kelly might just decide to barbecue some other kind of fish.
- Bad argument. One of Lisa’s brothers attending was a necessary condition but not a sufficient condition.
- First, Mark postponing his appointments is a necessary condition, not a sufficient condition. Second, Mark postponed “some” of his appointments. That could mean “most”, but we don’t know.
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