The flaw in the argument is that the conclusion is about all moments in time whereas the first premise was only about those moments in time when I insert a dollar bill into the machine. So sure, most of the time when I insert a dollar bill, the outlet is turned on (which would have been the valid conclusion). But that doesn't mean that most of the time the outlet is turned on. What, am I like just standing next to the machine 24/7 nonstop inserting dollar bills into it?

Before explaining this argument’s flaw, which requires a full breakdown of its structure, I want to emphasize a fundamental element of Parallel (and Parallel Flaw) questions: the correct answer’s claims must match the logical strength of the stimulus’ claims.

For this question, the spectrum of quantifiers – from some to most to all – is the relevant measure of logical strength: if a Parallel question’s stimulus features 2 some claims and a most conclusion, an answer choice that features 2 all claims and a some conclusion is wrong. Straight up.

In this stimulus, usually is a quantifier. It means “most of the time…” That makes the first sentence a most claim, the second sentence an all claim, and the third sentence a most claim.

This logic alone should narrow the field down to (D) and (E) during your shallow dip. Explanations for (A), (B), and (C) are below each answer – take a moment to identify their quantifier mismatches before revealing them.

Let’s talk about the argument’s actual structure. On a first read in English, the argument might seem completely fine:

Premise 1: When I insert a bill, most of the time there’s a squeak.
Premise 2: If there’s a squeak, the outlet must be on.*
________
Conclusion: The outlet is on most of the time.

*In Premise 2, “only when” acts like “only if.”

A completely fine argument is no good, though. This is a Parallel Flaw question. The flaw gets easier to see if you try to think in formal logic. Diagramming the conclusion is a bit ridiculous:

Premise 1: Insert Bill –most→ Squeak
Premise 2: Squeak → Outlet ON
________
Conclusion:   ???   –most→ Outlet ON

Perhaps you want to write “Outlet –most→ ON,” but you can’t just go around splitting up individual terms willy nilly. Like you can’t say “Insert –most→ Bill” and make formal logic moves around that.

Spoiler Alert: You don’t actually need to figure out what the conclusion’s deal is to distinguish between (D) and (E). You just need to pick the answer that makes you confused in the same way. You can diagram (E)’s conclusion like normal – it just links two terms from its premises. (D)’s is weirder.

Here’s what’s actually going on. There’s a subtle domain shift between Premise 1 and the Conclusion. Premise 1 applies to [moments in time when I am inserting a dollar bill]. The Conclusion applies to [all moments in time]:

Premise 1: If we consider all the moments in time when I am inserting a dollar bill, most of those moments involve some squeaking.

Conclusion: If we consider all the moments in time, most of those moments involve the outlet being on.

For another lens on the domain shift, the stimulus’ conclusion would be valid if it said:

Valid Conclusion: The electric outlet usually is turned on when I am inserting a dollar bill.

Here’s the argument again in formal logic emphasizing the domain shift:

Premise 1: [Moments in time when I am inserting a bill] –most→ Squeak
Premise 2: Squeak → Outlet ON
________
Conclusion: [Moments in time] –most→ Outlet ON

So yeah, that’s the template (D) will match. (B) matches the domain shift, too, by the way! It’s just wrong for other reasons.