Logical reasoning PrepTest 149 · Section 3 · Question 18

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Necessary Premise

Stimulus Summary:
Herbal medicines take a long time to work, but they're also toxic over a long time, so people taking them daily should skip a dose every once in a while.

Answer Anticipation:
This argument brings up the pros and cons of long-term herbal medicine usage—they work, but they are also toxic . . .

Don't worry, though, as the Herbalist has a solution! People who are on a daily herbal medicine regimen should skip a dose every once in a while to give the body time to recuperate.

There are two jumps here—one specific to this situation, and one that's more general. For the specific one, there's no indication that a single day of skipping the medication can counteract the toxic side effects. The argument is assuming that that's enough time to "flush" it out of the system and reset the issue.

The more general jump is in looking at the group in the conclusion and seeing if it matches the group from the premises. In the conclusion, the group in question is those who are taking herbal medicines daily. However, in the premises, the group it discusses is those who are taking herbal medicines daily for several months. The argument is therefore assuming that at least some of those daily herbal medicine takers are doing so for months at a time.

Answer Explanation:
This answer establishes that the group in the conclusion shares members with the group from the premises. If there are no people taking herbal medicine daily for long periods of time, then no one taking herbal medicine daily is at risk of the toxic side effects and there's no reason for anyone to skip a day.

Key Takeaway:
When the conclusion references a specific group, always make sure that the premises are dealing with the same group, or a group noted as representative of the group in the conclusion. Short of that, there's an assumption in the argument.

Incorrect. If anything, this answer cuts against the argument in stating that skipping doses would make these medicines work worse.

Incorrect. This answer, if anything, hurts the argument by establishing that skipping doses wouldn't be sufficient to avoid the toxic side effects.

Incorrect. This answer is too broad in stating that "[a]nyone" should take these medicines for several months. It's also a recommendation that's out of scope—the argument is about people taking these medicines skipping doses, not whether people should be taking them for long periods of time in the first place.

Incorrect. This answer establishes a necessary condition for skipping a dose. Since the conclusion is that a certain group of people should skip doses of their herbal medicines, it assumes there is a sufficient condition for that conclusion, not a necessary one.