Q3 - Unless the building permit

[ohthatpatrick]

What does the Question Stem tell us?
Sufficient Assumption

Break down the Stimulus:
Conclusion: New library won't be completed on schedule

Evidence: Permit can't be obtained by Feb 1
+
If permit not obtained by Feb 1 and there's no way to do some of the construction in less time than estimated, then the new library won't be completed on schedule

Any prephrase?
We have a rule that says "if X and Y don't happen, the library won't be finished on schedule". We have a fact that says "X won't happen". So we just need the other fact "Y won't happen". In this case, that means we need "no activities necessary for construction of the new library will be completed in less time than originally planned".

Answer choice analysis:
A) This does what we wanted.

B) This doesn't tell us whether other construction activities will be finished in less time than originally planned.

C) This doesn't tell us whether other construction activities will be finished in less time than originally planned.

D) This doesn't tell us whether other construction activities will be finished in less time than originally planned.

E) This doesn't tell us whether other construction activities will be finished in less time than originally planned.

The correct answer is A.

Takeaway/Pattern: Like almost all Sufficient Assumption questions, this is mathematically solveable before we look at the answer choices. The trickiest part is knowing how to conditionally symbolize "Unless X or Y happens, Z will happen." Unless = if not. So we're saying "If not true that (X or Y happens), then Z will happen". Saying that it's not true that "X or Y happened" is the same as saying they both didn't happen.

#officialexplanation

[aquyenl]

just had a quick question about the formal logic involved in this one. how do you diagram "Unless the building permit is obtained by Feb. 1 of this year or some of the other activities necessary for construction of the new library can be completed in less time than originally plan, the new library will not be completed on schedule"?

If no permit AND no activities finished early -> library not completed on time

why does that "or" switch to "and"?

[bbirdwell]

Quick answer for a quick question: "unless" = "if not"
And the "not" applies to everything in that part of the statement.

So if it says "unless A or B..."
We can say "not A (not or) not B," and the negation of "or' is "and."
So we have "not A and not B.

[nickwiggins]

I'm confused by this problem. We have this as the conditional statement:

Building completed on schedule --> Permit obtained by February 1 + Some other activities can be completed in less time than expected

And the contrapositive:

(Permit not obtained by February 1 or some of the other activities can't be completed in less time than expected --> Building won't be completed on schedule)

Doesn't the contrapositive fill the gap on its own. Because the permit isn't obtained by February 1, we know that the building won't be completed on schedule. Answer B seems to provide unnecessary affirmation of this.

[christine.defenbaugh]

Thanks for posting, nickwiggins!

So, that would be crazy weird, if the LSAT gave us a sufficient assumption question where the premise-conditional already guaranteed the conclusion, wouldn't it? That's our first clue that we've translated something incorrectly!

Let's take this conditional structure in a more fun example:

Unless I win the lottery or get a huge promotion, I won't be going to Fiji next year.

What does that mean? What if you see me in Fiji next year? What would you think? Probably something like 'hmmm....she must have either gotten that huge promotion, or she won the lottery - wonder which one it is?'

Unless statements can be thought of as a general promise with a safe harbor - outside the safe harbor, the promise applies. Within the safe harbor, we don't know what happens. So, "I'll walk the dog, unless it rains" has the promise that "I'll walk the dog", and the safe harbor "unless it rains". If we AREN'T in the safe harbor, I have to keep my promise: If it's not raining, then I will walk the dog. If I've failed my promise, I need to be in the safe harbor to get away with it: If I don't walk the dog, then it must be raining.

When an unless has an 'and' or 'or' statement, that changes the safe harbor. "Unless X or Y" gives me TWO potential safe harbors, either one of which could get me off the hook for my promise. But if NEITHER safe harbor is in play, then my promise still stands. Thus, "If no X AND no Y --> (promise)".

"Unless X and Y" would give me a single safe harbor - X and Y BOTH would have to be true together for the safe harbor to get me off the hook for my promise, so if we're missing even just one of them, that's enough to know that my promise is still in play. Thus, "If no X or no Y --> (promise)".

Okay, so the structure Unless A or B, C translates to:

If not A AND not B, then C
If not C, then A OR B.

Now that we understand that, we can diagram this argument correctly:

PREMISE:
(conditional): If NO (Feb1 permit) AND NO (activities = less time than planned) --> NO (completed on schedule)
(fact): no Feb1 permit
CONCLUSION: no completed on schedule

We're missing the second part of the 'and' trigger! For this conclusion to make sense, we'd need to know the activities can't be completed in less time than planned! That's precisely what (A) gives us.

Let's take a look at each wrong answer choice:

(B) Probably? That won't guarantee the conclusion!
(C) This suggests that we can't get the permit by Feb 1, but we already knew that!
(D) Again, this might make us think we're unlikely to get the permit by Feb 1, but we already knew that!
(E) While convincing the authorities to let us start construction early might help get things done on time, even without it, we might be able to get a bunch of things done in less time than originally planned!

Does that help clear things up a bit? Statements that include "unless" and "and/or" always take a bit of care!

[Mikey]

Ok so I see how A is correct, even though I eliminated it without question. But how is C not sufficient enough to make the conclusion be properly drawn? This question confused me when I saw that I got it wrong because I was confident about C.