Student: If a person has an immunity to infection by a microorganism, then that microorganism does not cause them to ...

Ryan on October 18, 2019

Why is D correct? Why is B incorrect?


1 Reply

Irina on October 18, 2019


The argument tells us that if A then B, thus if B is true, then A must be true.

If a person has immunity (A), then they develop no symptoms (B).
People exposed to staphylococcus develop no symptoms (B).
Therefore, they must have immunity (A).

This is a logical fallacy of affirming the consequent/ mistaken reversal. Let's compare it to options (B) and (D)

Advertisers (A) try to persuade people that certain claims are true (B).
Writers of fiction are not advertisers (~A).
Therefore, they never try to persuade people (~B).

If A then B
Therefore, ~B

This is also an invalid argument, but the type of logical fallacy is different from the stimulus.

When business owners are subjected to taxation (A), they become less willing to expand their business (B).
Business expansions are in decline (B)
Therefore, taxes are too high (A)

If A then B
Therefore, A

This flawed reasoning pattern is identical to the stimulus and is, therefore, the correct answer.