If Iris is scheduled for the next day after Harry, which one of the following lists all those days any one of which c...

Alexandra May 8, 2020

Is it necesarry to check the contrapositives.

When you are going through checking the rules, specifically on question 8, you are checking the original rule and then just skipping over the contrapositive. So my question is: is it necessary to check every rule AND it's contrapositive? I was doing this during practice but if it means that the rule passes and the contrapositive automatically passes then it would definitely save time during the test to only check the 2 rules instead of the four, if that makes sense!

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BenMingov May 8, 2020

Hi Alexandra, thanks for the question.

I totally get what you mean in terms of saving time. And while writing the contrapositives out is definitely optional, it is strongly recommended.

What you are describing is when the original rule does not apply, then by virtue of this, the contrapositive would not either. However, what the contrapositive does help us do is realize when a rule does apply much faster. We don't need to remember to check for the negated necessary condition in each instance from memory, it will be laid out right in front of us.

Overall it just makes our deductions that much faster and more accurate. So again, up to you what you choose, but I do recommend it.

I hope this helps. Please let me know if you have any other questions or would like me to elaborate further.

Alexandra May 10, 2020

I would definitely write out all the contrapositives when doing the question set up but is it necessary to check the contrapositives with every answer as well as the original rule? Like when finding a must be true or a cannot be true.