Self-study
Jim's teacher asked him to determine whether a sample of a substance contained iron. ███ ████ ████ ███████ ███████ █████ ██ ██ ██████ █ ██████ ████ ███ ██████████ ███ █████████ ████ ███ █████████ ███ ███████ █████ ███████ ███ █████████ ██████ ████████ ██ ███ ███████
Summarize Argument: Phenomenon-Hypothesis
Jim concludes that a substance contains iron because it’s attracted to a magnet, and iron is a material that’s attracted to magnets.
Identify and Describe Flaw
This is a cookie-cutter example of an argument mistaking a sufficient condition for a necessary condition. Jim treats “containing iron” as though it were a necessary condition for being magnetic, even though it’s only sufficient. In other words, he ignores the possibility that the substance contains a magnetic material other than iron.
1.
Jim's reasoning is questionable in ████ ██ █████ ██ ████████ ███ ███████████ ████
a
iron sometimes fails ██ ██ █████████ ██ ███████
This possibility is irrelevant because the iron was attracted to the magnet in this case.
b
iron is attracted ██ █████ ███████ ███████ ███████
The argument is only concerned with whether being attracted to a magnet is enough to prove that a substance contains iron. Whether iron is also attracted to other objects has no bearing on that issue.
c
the magnet needed ██ ██ ████████ ██ █ ███████ ███
Even if this were a requirement, the magnet would have had to have been oriented correctly since it attracted the substance in this case.
d
magnets attract substances █████ ████ ████
This possibility undermines the conclusion because it means that the substance could be attracted to the magnet even if it contains some magnetic material other than iron.
e
some magnets attract ████ ████ ████████ ████ ██████
The argument is only concerned with whether the magnet attracts the substance or not; the degree to which it attracts the substance is irrelevant.