Logical reasoning PrepTest 144 · Section 4 · Question 12

Incorrect. The argument only relies on lavender doing this, not on other scents. Other scents are out of scope.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Necessary Premise

Stimulus Summary:
Lavender reduces stress, which strengthens the immune system, which fights illness. Therefore, those who regularly smell lavender have their incidence of illness reduced.

Answer Anticipation:
An interesting question in that conclusion is causal—which would usually mean a correlation/causation flaw—but the premises are also causal! As such, there's no correlation/causation flaw here, as a causal conclusion can be justified by causal premises.

When there are several causal statements that chain together to back up a causal conclusion, we should look to see if there are any term shifts between the causal chain in the premises and the causal relationship in the conclusion. However, here, the premise discusses lavender and illness, and the conclusion also discusses those ideas, so there's no term shift.

So what are we left with? Well, the last thing we can look at is that group in the conclusion—those who regularly inhale lavender. Why does the argument believe that their incidence of illness will be reduced by this? Because it'll reduce their stress levels. However, it's possible that this group doesn't have high enough stress levels to cause immune system issues. If they're all pretty low-stress to begin with, inhaling the lavender won't lower their incidence of illness, as they don't have that cause of illness to begin with.

Answer Explanation:
This answer highlights the assumption in the argument that those who regularly inhale lavender have the noted cause of a weakened immune system that lavender helps counteract—stress. If those who regularly smell lavender are generally unstressed, then the lavender won't lower their risk of disease as stress wasn't raising it to begin with.

Key Takeaway:
Causal premises can support causal conclusions. Causal chains that lead to causal conclusions will frequently be flawed because of a term shift between those premises and the causal relationship in the conclusion. And always track the groups being discussed, as they're relevant to analyzing the logic.

Incorrect. This answer is about a subset of people who smell lavender—those who do so to intentionally relieve stress, and it compares their risk of illness to the average. However, the argument doesn't state that those who regularly smell lavender have a lower incidence of disease than those who don't—it says they have a lower incidence of disease than they would if they didn't regularly smell lavender. Therefore, this answer comparing their incidence of illness to other people is out of scope.

Incorrect. While the stimulus establishes that destressing people is one mechanism by which lavender reduces susceptibility to illness, it doesn't state that it's the only one or even the primary one. It's possible that lavender has direct medicinal properties that counteract certain diseases.

Incorrect. If anything, this undermines the argument by bringing up the possibility that lavender doesn't always reduce the incidence of illness.