Self-study
Student: Support If a person has an immunity to infection by a microorganism, then that microorganism does not cause them to develop harmful symptoms. █████ ████ ██████ ███ ███████ ██ ██████████████ ███████ ██████████ ███ ███████ █████████ ██ ███████ ████ ████ ████ ██ ████████ ██ █████████ ██ ████ ██████████████
Method of Reasoning
The student states that anyone with an immunity to a microorganism will not develop harmful symptoms after being exposed to that microorganism. The student then concludes that some people are immune to staphylococcus because those people do not develop harmful symptoms after being exposed to that microorganism.
Identify and Describe Flaw
This student commits the flaw of sufficiency-necessity confusion. In his premises, he defines a person having an immunity to a microorganism as sufficient to know that they will not develop harmful symptoms from that microorganism. However, in his conclusion, he takes a person not developing harmful symptoms from an encounter with a microorganism to mean that the person has an immunity to that microorganism.
25.
The student's argument is most ███████ ██ ███ ██████ ███████ ██ █████████ ██ █████ ███ ██ ███ ██████████
a
Everything morally right ██ █████ ███ ████ ███████ ████ ████ █████ ███ █████████ ██ ████████ ███ ███ █████ █████ ████ ███████ █████ ███████ ██ ███ █████ ███ █████████ ██ █████████
Wrong flaw. This answer choice tried to contrapose a “some” relationship the way you would a normal conditional relationship; this cannot be properly inferred from the premises it provided. This answer choice is different from the flaw in the stimulus because it involves a “some” relationship, whereas the stimulus has none, and it does not use a confirmation of the necessary condition to try to prove the sufficient condition in the conclusion, as the stimulus did.
b
Advertisers try to ████████ ██████ ████ ███████ ██████ ███ █████ █████ ███████ ██ ███████ ███ ███ ████████████ ████ ████████ █████ ███ ██ ████████ ██████ ████ ███████ ██████ ███ █████
Wrong flaw. This answer choice confuses sufficiency and necessity by assuming that a negated sufficient condition leads to a negated necessary condition. This is different from the stimulus, where the author affirms their necessary condition in the premises in order to imply the sufficient condition in the conclusion.
c
Isabel said that ███ █████ ████ ███ ███████████ ██████████ ███████ ███ ███ ███ ██ ███ ███████ ██████████ ██████ █████ ███████ ██ ██████████ ███ █████████ ███ ██████ ██ █████ █████ ████
No flaw. This answer choice says that medication leads to either a disease being cured or the alleviation of its symptoms. If Isabel is ill, she has not had her disease cured nor its symptoms alleviated. If you negate both necessary conditions for an either/or statement, you can negate the sufficient condition, which the author did in their conclusion by saying that Isabel did not take the medication.
d
When business owners ███ █████████ ██ █████████ █████████ ████ ██████ ████ ███████ ██ ██████ █████ ███████████ ███ ██████ ███████ ██ ████████ ██████████ ████ █████ ████ █████ █████ ███ ███ █████
This answer choice commits the flaw of sufficiency-necessity confusion. It confirms its necessary condition, a decline in/lack of expansion, in order to imply the sufficient condition, excessive taxation, in the conclusion.
The author uses a decline in business expansion and lack of willingness among businesses to expand interchangeably as the necessary condition here, despite not telling us that these are equivalent. Even though the author does not perfectly satisfy his necessary condition, the mistake made here is still closest to the one in the stimulus. Finally, this argument does not use a subset, like the stimulus did in its narrowing down from all diseases to staphylococcus, but the conditional structure of sufficiency-necessity confusion makes this the right answer.
e
Studies show that ███████ ████ ██ ████ █████ █████ ████ █████ ████ ███ █████ ██████ ████ ██████████████ ████ █████ ████ ███ █████████ ██████ ██ ██ ████ █████ ██ ██████████ ████████
Wrong flaw. This argument’s conclusion is not supported by its premise at all. The prevalence of handwashing among a type of healthcare professional shows no sign that handwashing is or is not effective against the spread of disease. This differs from the stimulus because there is no conditionality, and therefore no sufficiency-necessity confusion that would match that of the stimulus.