Logical reasoning PrepTest 101 · Section 2 · Question 21

Flawed

Strengthen with Sufficient Premise Questions / Sufficient & Necessary Questions

Gambling law → ~Enforceable

~Effective → ~Should be a law

Strengthen with Sufficient Premise questions frequently have conditional logic, so we should be on the lookout. And while this argument isn’t as clearly conditional as many such questions are, there are conditional indicator words (“all”, “when”).

Walking through the argument, we can simplify the first sentence to our first conditional - despite the extraneous information, the logic of that statement applies to all gambling laws (sufficient condition), stating that they are impossible to enforce (necessary condition).

The second sentence starts with an aside (“notwithstanding”) before getting to the conditional - “when” (if) a law isn’t effective, then it shouldn’t be a law. We now have our second conditional premise.

From that, we get to the conclusion - there shouldn’t be gambling laws. We wrote it out in a way that matched up with our premises in our Summary.

With that noted, we can see that the conclusion lines up with the terms in the premises - those premises talk about gambling laws and what shouldn’t be law. Since the key terms in the conclusion are established in the premises, the gap in the logic must be between the two premises.

Taking a look, we can see that the first ends with ~Enforceable and the second starts with ~Effective. However, those concepts are never connected - maybe an unenforceable law can be effective. For example, it might convey that a certain behavior is “bad” and thus get people to stop doing it even without the threat of enforcement.

Since the conditional chain in the premises is missing a link, we should find an answer that brings it (or the contrapositive) up:

~Enforceable → ~Effective

Effective → Enforceable