#11 - John works five days each week except when on vacation

[zkracz]

Rachel,

You are right, but unless i'm wrong that only demonstrated that it is possible for John to have the schedule he describes without assuming E, when the stimulus is asking for us to make it so that the argument MUST be true. It is equally possible for him to have the same schedule without assuming D either, but that doesn't mean we don't have to assume D. The issue is the stimulus asks which must be assumed - it needs an assumption which necessitates its conclusion, which I demonstrated both E and D are required for. If it is possible for John to have not worked at the insurance company Monday through Thursday, then the argument is false - it said that he must work those days. So I agree that your arrangement is possible, but it only shows that its possible that he worked those days, which isn't the strength of conclusion the stimulus asks for.

Am I missing something here? Must means that no alternative exists which meets all of the conditions, and unless we assume both D and E, no such alternative exists.

[Jeff Wren]

Hi zkracz,

You wrote "unless i'm wrong that only demonstrated that it is possible for John to have the schedule he describes without assuming E, when the stimulus is asking for us to make it so that the argument MUST be true."

Based on your comment, I think that you may be confusing Assumption questions (which are sometimes referred to as Necessary Assumption questions) with Justify questions (which are sometimes referred to as Sufficient Assumption questions). The question is not asking for an answer that proves the conclusion/makes the argument valid. Instead, it's asking for a statement that is necessary for the argument, as indicated by the word "depends" in the question stem.

If it is possible "for John to have the schedule he describes without assuming E," (which it is ), then Answer E does not need to be assumed and is therefore the wrong answer.

As discussed in earlier posts, Answer D does need to be assumed because if John worked on Saturday or Sunday (as well as Friday, which he always works), then there would be no way that he could work Monday-Thursday because that would be more than 5 days in one week, and we know he always works exactly 5 days a week (when not on vacation and not during holidays).

Understanding the distinction between Assumption and Justify questions is extremely important as people often confuse the two questions types and then approach the answers incorrectly. If you're at all unclear about this topic, I'd suggest reading up on this topic in "The Logical Reasoning Bible" or checking out the relevant lessons of the PowerScore course.

[zkracz]

Precisely - E is a necessary assumption, because unless we assume E, the possibility that I outlined is still in play. Let us negate E - does the argument in the stimulus still hold? No, no it doesn't, because the stimulus is saying that John's schedule must be as he described. I did not say that E will necessitate the situation that John described, just that unless we assume E in addition to D, it is impossible to conclude what he is saying because we have the possibility that John worked as a blacksmith some day from Monday to Thursday that John did not work at the insurance company.

I am saying that E is a necessary assumption, and think I was able to prove that it is.

[zkracz]

In this problem, a necessary assumption is any assumption for which its rejection would enable the schedule to be in any arrangement except how John describes it.

This is why D is a necessary assumption - while its possible that the schedule could be as John described, it isnt a "must". All I am doing is saying this same thing also applies to E, because if we negate E, we can produce a schedule that is not as John described and it is therefore not true that the schedule must be as john described.

[Dana D]

Hey Zkracz,

I would think of it this way - the question asks us which answer choice the argument depends on. That means that for the correct answer, you can add it into the stimulus and say "assuming xyz, the conclusion must be true." In this case, that would mean saying "assuming answer choice [X], John must have worked at the insurance company M/Tue/Wed/Thurs last week."

If we look at answer choice (E) with that in mind, we'd say "assuming there are no days John worked at both the insurance and the blacksmith's, he must have worked at the insurance company M/Tues/Wed/Thurs." But that statement still isn't true - even without working at both companies in the same day, John could potentially have worked on Saturday or Sunday. We can't say for sure that he worked M/Tues/Wed/Thurs when he could have actually worked Sat or Sun.

Compare that to the correct answer, choice (D) - "assuming John worked neither Saturday nor Sunday, he must have worked at the insurance company M/Tues/Wed/Thurs." Now that argument makes sense, because John has to work exactly 5 days a week and we are saying he didn't work Sat or Sunday - there are exactly 5 days left in the week and John must work each of them.

Does that make sense?