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Anatomical bilateral symmetry is a common trait. It follows, therefore, that it confers survival advantages on organisms. After all, if bilateral symmetry did not confer such advantages, it would not be common.
What is the flaw here?
The argument restates rather than proves. The conclusion is a premise too. We starting out by assuming that the conclusion is true and then saying that the conclusion is true.
If A (bilateral symmetry) were not B (confer survival advantages), A (bilateral symmetry) would not be C (common).
A (bilateral symmetry) is C (common) so A (bilateral symmetry) is B (confer survival advantages).
Note that we did not try to prove that “A is C implies A is B”. We did not explain the connect between C and B. For our reason, all we said is that if A were not B, it would not be C. So we are starting out by taking the conclusion to be true.
This is called circular reasoning. It is a kind of logical fallacy, a flaw in the logic. You begin with what you are trying to prove. Circular argument uses its own conclusion as one of its premises.
Why is it good to understand circular reasoning? Mimic the reasoning argument could require you to identify such a flawed reasoning and find the argument that mimics it.
Continuing with the previous example:
Anatomical bilateral symmetry is a common trait. It follows, therefore, that it confers survival advantages on organisms. After all, if bilateral symmetry did not confer such advantages, it would not be common.
The pattern of reasoning in which one of the following arguments is most similar to that in the argument above?
(A) Since it is Sawyer who is negotiating for the city government, it must be true that the city takes the matter seriously. After all, if Sawyer had not been available, the city would have insisted that the negotiations be deferred.
(B) Clearly, no candidate is better qualified for the job than Trumbull. In fact, even to suggest that there might be a more highly qualified candidate seems absurd to those who have seen Trumbull at work.
(C) If Powell lacked superior negotiating skills, she would not have been appointed arbitrator in this case. As everyone knows, she is the appointed arbitrator, so her negotiating skills are, detractors notwithstanding, bound to be superior.
(D) Since Varga was away on vacation at the time, it must have been Rivers who conducted the secret negotiations. Any other scenario makes little sense, for Rivers never does the negotiating unless Varga is unavailable.
(E) If Wong is appointed arbitrator, a decision will be reached promptly. Since it would be absurd to appoint anyone other than Wong as arbitrator, a prompt decision can reasonably be expected.
We established that the above pattern of reasoning has circular reasoning flaw. Let’s consider each option to find the one which has similarly flawed reasoning.
(A) Since it is Sawyer who is negotiating for the city government, it must be true that the city takes the matter seriously. After all, if Sawyer had not been available, the city would have insisted that the negotiations be deferred.
Here is the structure of this argument:
If A (Sawyer) were not B (available), C (city) would have D (insisted on deferring).
Since A (Sawyer) is B (available to the city), C (city) does E (takes matter seriously)
Obviously, the argument structure is not the same as in the original argument.
(B) Clearly, no candidate is better qualified for the job than Trumbull. In fact, even to suggest that there might be a more highly qualified candidate seems absurd to those who have seen Trumbull at work.
Here is the structure of this argument:
A (people who have seen Trumbull at work) find B (Trumbull is not the best) absurd.
B (Trumbull is not the best) is false.
This is not circular reasoning. We have not assumed that B is false in our premises. We are saying that people think B is absurd. This is flawed logic too but it is not circular reasoning.
(C) If Powell lacked superior negotiating skills, she would not have been appointed arbitrator in this case. As everyone knows, she is the appointed arbitrator, so her negotiating skills are, detractors notwithstanding, bound to be superior.
Here is the structure of this argument:
If A (Powell) were not B (had superior negotiating skills), A (Powell) would not have been C (appointed arbitrator).
A (Powell) is C (appointed arbitrator) so A (Powell) is B (had superior negotiating skills).
Note that the structure of the argument matches the structure of our original argument. This is circular reasoning too. We are saying that if A were not B, A would not be C and concluding that since A is C, A is B. The conclusion is already taken to be true in the argument.
Hence (C) is the correct answer. Nevertheless, let’s look at the other two options too.
(D) Since Varga was away on vacation at the time, it must have been Rivers who conducted the secret negotiations. Any other scenario makes little sense, for Rivers never does the negotiating unless Varga is unavailable.
Here is the structure of this argument:
If A (Varga) is B (available), C (Rivers) does not do D (negotiate).
A (Varga) was not B (available) so C (Rivers) did D (negotiate).
The logic is flawed – the premise tells us what happens when A is B. It does not tell us what happens when A is not B. So we cannot conclude anything about what happens when A is not B.
But this is not circular reasoning. Hence it is not the answer.
(E) If Wong is appointed arbitrator, a decision will be reached promptly. Since it would be absurd to appoint anyone other than Wong as arbitrator, a prompt decision can reasonably be expected.
Here is the structure of this argument:
If A (Wong) is B (appointed arbitrator), C (a decision) will be D (reached promptly).
A (Wong) not B (appointed arbitrator) would be absurd so C will be D.
Again, the argument is brute force but it is not circular reasoning. “A not B would be absurd” is not a convincing reason so the argument is not strong but in any case, we don’t have to worry about it since it doesn’t use circular reasoning.
Take a look at this question for practice:
Dr. A: The new influenza vaccine is useless at best and possibly dangerous. I would never use it on a patient.
Dr. B: But three studies published in the Journal of Medical Associates have rated that vaccine as unusually effective.
Dr. A: The studies must have been faulty because the vaccine is worthless.
In which of the following is the reasoning most similar to that of Dr. A?
(A) Three of my patients have been harmed by that vaccine during the past three weeks, so the vaccine is unsafe.
(B) Jerrold Jersey recommends this milk, and I don’t trust Jerrold Jersey, so I won’t buy this milk.
(C) Wingz tennis balls perform best because they are far more effective than any other tennis balls.
(D) I’m buying Vim Vitamins. Doctors recommend them more often than they recommend any other vitamins, so Vim Vitamins must be good.
(E) Since University of Muldoon graduates score about 20 percent higher than average on the GMAT, Sheila Lee, a University of Muldoon graduate, will score about 20 percent higher than average when she takes the GMAT.
