# No occupation should be subject to a licensing requirement unless incompetence in the performance of tasks normally c...

Parker on September 27, 2018

Hi, can someone tell me why answer choice D doesn't work?

Replies

Mehran on September 27, 2018

@Parker-Zopp let's diagram the principle first:

"No occupation should be subject to a licensing requirement unless incompetence in the performance of tasks normally carried out within that occupation poses a plausible threat to human health or safety."

Unless (1) introduces necessary and (2) the negation of the other part of the sentence is our sufficient condition, so we would diagram this principle as follows:

OSLR ==> IPTHHS
not IPTHSS ==> not OSLR

OSLP = occupation subject to a licensing requirement
IPTHSS = incompetence in the performance of tasks normally carried out within that occupation poses a plausible threat to human health or safety

This is Must Be True Principle question so we are looking for an answer choice that properly applies this principle.

Remember, there are only two ways to validly apply a general principle:

(1) invoke S to conclude N (positive argument structure)
(2) establish the nonexistence of N to conclude the nonexistence of S (contrapositive argument structure)

Notice that you can never conclude the sufficient condition.

We can conclude the nonexistence of the sufficient condition by invoking the contrapositive (i.e. not N ==> not S).

Just based on this we can eliminate (D) because (D)'s conclusion is "hair stylist should be subject to a licensing requirement" (i.e. OSLR), which is the sufficient condition.

Remember, don't just reverse! And that is what you are doing if you are concluding the sufficient condition in any scenario.

Hope that helps! Please let us know if you have any other questions.

Justin on June 16, 2020

I had thought that the combination of this "No" statement and the "unless" statement would lead to a different condition. Does someone mind explaining how the negation works with the No and the Unless?

Ravi on February 9, 2022

You can just focus on the "unless" here when diagramming. Unless means the same thing as "if not," so you can pick either idea, negate it, and make it the sufficient condition. If we negate the first idea, which is "no occupation should be subject to a licensing requirement," we have

Subject to a licensing requirement

Let's now put that in the sufficient condition:

Subject to a licensing requirement-->

Now, we just have to put the other idea in the necessary condition of the statement.

Doing so, we get

Subject to a licensing requirement-->incompetence poses threat