It is false that some serial killers are not deranged psychopaths. Therefore, all serial killers are deranged psychopaths.
A) Invalid, existential fallacy.
B) Invalid, illicit contrary.
C) Valid.
D) Invalid, illicit contradictory.
E) Invalid, illicit subalternation.

Question

Quizplus · Accepted Answer

This is a valid categorical syllogism. The premise "It is false that some serial killers are not deranged psychopaths" is an A-statement, meaning it is an affirmative statement about all of a particular group. The conclusion "all serial killers are deranged psychopaths" is also an A-statement. Since the premise and conclusion have the same quantity and quality and share the middle term "deranged psychopaths," the syllogism is valid.

It Is False That Some Serial Killers Are Not Deranged