Contrapositives and Circular Reasoning?

[zainrizvi]

Can somebody explain when taking the contrapositive is valid reasoning, and when it incurs circular reasoning? I'm getting a bit confused by the two concepts.

[chike_eze]

Can somebody explain when taking the contrapositive is valid reasoning, and when it incurs circular reasoning? I'm getting a bit confused by the two concepts.

Contrapositive is implied when you are given a conditional relationship between concepts in a statement. You usually take contrapositives of conditional statements in an argument or fact-set. For example, If Shelly goes to the market, she will buy apples. This translates to:

Shelly goes to market --> Shelly buys apples
Shelly not buy apples --> Shelly not go to market (contrapositive)

Circular reasoning on the other hand, is flawed reasoning that applies to the whole argument, i.e., Premise -> Conclusion

For example, Shelly is a great golfer because she is an excellent golfer. Premise and conclusion are equivalent.

So I guess, the way I look at it is... contrapositives apply to conditional statements in arguments (or fact-sets), and circular reasoning applies to the whole argument (with/without conditional statements).

[noah]

great explanation

[zainrizvi]

Can anyone give an example of circular reasoning using conditional logic?

[chike_eze]

Can anyone give an example of circular reasoning using conditional logic?

You are a great golfer if you score 5 under par. We all know that I am a great golfer, therefore I am a great golfer!

5 under par --> Great Golfer
Great Golfer --> Great Golfer

Not sure how practical this example is...

Question: Are you a great golfer?
Answer: Yes I am
Question: How do you know you are a great golfer?
Answer: Because I am a great golfer
Question: Do you score 5 under par?
Answer: Huh? That doesn't matter, I am great!

[ManhattanPrepLSAT1]

Hey great discussion here. I just wanted to point out that sometimes it's difficult to spot the difference between a circular argument that uses conditional logic and an argument that mistakes a sufficient for necessary condition.

Suppose you're on a Match the Flaw question and you're given the following argument in the stimulus.

Good jobs are available in the field of academics only to those people with college degrees. Therefore, if one gets a college degree one is sure to be able to find a good job in the field of academics.

GJA ---> CD
---------------
CD ---> GJA

Notation: GJA = good job in academics, CD = college degree

Now suppose you go rummaging through the answer choices and come across the following answer choice.

Anyone who has been convicted of a felony, is not eligible to serve on the supervisory committee, since serving on the supervisory committee requires that one has never been convicted of a felony.

CF ---> ~SC
--------------
SC ---> ~CF

Notation: CF = convicted of a felony, SC = supervisory committee

The first argument is mistaking a sufficient for necessary condition, whereas the latter argument is circular reasoning in that the conclusion merely restates the evidence in a different way.

Sometimes these two can be difficult to spot and when you're on a Match the Flaw question that contains either circular reasoning or mistaking a sufficient for necessary condition, the test-writer is bound to ask you spot the difference.

Hope that helps!