Self-study
One test to determine whether a person has been infected with tuberculosis consists of injecting the person with proteins extracted from the tuberculosis bacterium. ████ █ ██████ ███ ████ ████████ ██ █ ██████████ ███ ████████ ██████ ██████ ████████████ ██████████ ███████ ████████ ███████ ██ ████ █████████ ███ ███████ ███ ██████████ ████ ███████████ ████ █████ █████ ██ ███ ████ ███ ███████ ██ █ ████ ██████████ ██ ███ █████████ █████ █████ ███ ██████████ ███ ████████ ███ ████ ████████ ████ ██████ ███ ██████ ██ ████ ██████ ██ ██ █████████ ████ ███ ████████████ ████████ ███ ████ ████████ ████ █████████████
Summary
The physicians conclude that anyone whose skin becomes irritated when injected with tuberculosis proteins has had tuberculosis. This is because people’s immune systems recognize proteins from bacteria that previously infected them. Furthermore, this immune system reaction also occurs (and leads to skin irritation) when someone has had tuberculosis and is then injected with tuberculosis proteins.
Notable Assumptions
The premises establish tuberculosis infection as a sufficient condition for skin irritation from this test, but not a necessary condition. However, the conclusion treats infection as being necessary. This means the physicians are assuming that there is no other reason someone’s skin would become irritated when injected with tuberculosis proteins, other than having had tuberculosis.
6.
Which one of the following ██ ██ ██████████ ██ █████ ███ ███████████ █████████ ████████
a
All of the ████████ ███████ ██ ███████████████ ████████ ███ ██ ██████████ ██ ███ ██████ ██████ ███████
The argument is only concerned with the proteins in tuberculosis bacteria, so this kind of claim about all proteins in all disease-causing bacteria is too broad to be necessary.
b
Localized skin irritations ███ █ ██████████████ ███████ ██ ████████████ ██ ████ ███████
Whether or not skin irritation is usually a symptom of actual tuberculosis infection is irrelevant, because the argument is only concerned with reactions to the tuberculosis test.
c
The ability of ███ ████████ ███████ ██ ███ ████████████ █████████ ██ ███████ ███ ████ ██████████ ██ █████████ ██ ████ ██████████
In other words, there is no other bacterium which would lead to skin irritation when someone is injected with tuberculosis proteins. This is necessary because otherwise, we couldn’t conclude that a reaction meant tuberculosis and not some other bacterium.
d
Some people who ████ ████ ████████ ████ ████████ █████████ ████ ███ ████████████ █████████ ████ ████████ ████████████ ██ █ ██████ ██ ███ ██████████
Whether or not it’s possible to get tuberculosis from being injected with tuberculosis proteins is irrelevant to whether a skin reaction truly indicates tuberculosis.
e
The body's immune ██████ ██████ █████████ ██████████ ████████ ██████ █████ ███ ██████████ ██████████ ██ ███ ████████ ██ █████ █████ ████████ ██ ████████
What exactly it means to be “infected” by bacteria such that your immune system will recognize those bacteria isn’t relevant, because the argument doesn’t depend on that exact of a definition of “infected.”