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Course: LSAT > Unit 1
Lesson 7: Logical Reasoning – Video lessons- Identify the conclusion | Video lesson
- Identify an entailment | Video lesson
- Strongly supported inferences | Video lesson
- Disputes | Video lesson
- Identify the technique | Video lesson
- Identify the role | Video lesson
- Identify the principle | Video lesson
- Match the structure | Video lesson
- Match principles | Video lesson
- Identify a flaw | Video lesson
- Match flaws | Video lesson
- Necessary assumptions | Video lesson
- Sufficient assumptions | Video lesson
- Strengthen | Video lesson
- Weaken | Video lesson
- Helpful to know | Video lesson
- Explain | Video lesson
- Resolve a conflict | Video lesson
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Necessary assumptions | Video lesson
Learn how to approach a question that asks you to identify a necessary assumption of an argument on the logical reasoning section of the LSAT.
Want to join the conversation?
- When a question stem asks "The argument assumes which one of the following"/ How should I attack it?(3 votes)
- Does necessary assumption mean that we will have to assume something that would weaken the author's argument?(1 vote)
- necessary assumption should strengthen the author's arguments and help the argument(3 votes)
- is it good to negate all the answers to find the correct one(1 vote)
- And when negating the answer choice to check and see if it weakens the argument, why don't we take out the not in the sufficient condition ?(1 vote)
- I'm confused as to why answer choice C is wrong. If income tax are not lowered then income will decrease even further that means people will be reluctant to spend. This is what the argument is stating(1 vote)
Video transcript
- [Instructor] To determine
what kind of question this is let's jump below the passage
to the question itself. Which one of the following
is an assumption required by the economist's argument? This idea of an assumption
being required is our signal that we're dealing with a
necessary assumption question. So, the answer is gonna be
a claim that has to be true in order for the argument
to have a chance to work. The other four choices will be claims that just aren't necessary
to the arguments survival. Either because they're not
relevant, or they're too strong to be necessary or some reason like that. So, pause your video now if you'd like to try this question on your own. Otherwise, let's move
on to the explanation. Okay, let's read the stimulus together. When reading for a necessary assumption, you'll want to rally
understand the main conclusion and evidence of the speakers argument. And, I want you to see if you
can detect any kind of gap between the conclusion and evidence. So the economist says,
"Our economy's weakness "is the direct result of
consumers' continued reluctance "to spend, which in turn
is caused by factors "such as high-price goods and services." "This reluctance is exacerbated
by the fact that the "average income is significantly lower "than it was five years go." "Thus, even though it is
not a perfect solution, "if the government were
to lower income taxes, "the economy would improve." Let's mark our conclusion first. We have a pretty nice
key word here with 'thus' and just to double check
that it's actually our main conclusion, we can confirm
that everything coming before it is meant to lead up to,
or support this conclusion. So, the economist makes a
sort of conditional prediction that if the government
lowered income taxes, the economy wold improve. Okay, why does the economist
believe that this would happen? Well the answer to that
question is our evidence. Now when we're identifying evidence, we don't want to just robotically
regurgitate everything that we see in the rest of the passage. We want to really simplify it and understand it for ourselves. So basically, one piece
of evidence is this sort of chain reaction that high
prices leads to people not wanting to spend and that
leads to our economic weakness. The second piece of evidence
is that, that reluctance to spend is made worse
by the lower incomes. So to find a gap in an argument,
it can be really helpful to look for an idea or concept that kind of comes out of no where. So look at our progression here. On the evidence side were
talking about lower incomes, higher prices, reluctant to
spend, economic weakness. Okay, what's the star player
of the conclusion though? The spotlight of the conclusion is on this recommendation to lower income taxes. Well wait a minute. We never talked about lowering
income taxes in the evidence. But the economist doesn't
seem to notice that. That means that the economist is assuming, or taking for granted,
that lowering income taxes is somehow related to something
discussed in the evidence. So the economist here believes
that if the government lowered income taxes, something from the evidence would happen. What is that thing? Well, income in the evidence is connected to reluctant to spend. We see that in the second sentence. So the economist is assuming
that if the government lowered income taxes, consumers would
be more willing to spend. Because think about it, if
they weren't more willing to spend, this conclusion that
the economy would improve doesn't have a good leg to stand on. So it's necessary for
this relationship to exist in order for the argument to work. We have a super strong prediction here and that's a great goal to have, for necessary assumption questions. If you have a super strong
prediction you won't get lost in all the choices. So let's find our match. A, increasing consumer spending
will cause prices for goods and services to decrease. That's not a match for our prediction, so we can get rid of it. As an extra note this
relationship doesn't work because in the passage we
learned that high prices cause reluctance to spend,
but this choice is that willingness to spend causes lower prices. That relationship is backwards. B, if consumer spending increases, the average income will increase. This doesn't match our prediction either. And, it's actually backwards. The economist is assuming
that a higher income will cause higher higher
spending, but this choice has that relationship backwards, saying that higher spending
will cause higher income. C, if income taxes are
not lowered, consumers' wages will decline even further. This doesn't match our prediction either, so we can cross it off. Once again, the economist is
assuming that a higher income will cause higher spending. But this choice is basically
saying that income taxes don't get reduced, peoples
income will keep falling. That doesn't have to be true
for the argument to work. Let's actually negate this choice and see what happens to the argument. Let's say that if income
taxes are not lowered consumers wages won't
decline even further. So we didn't lower taxes, but the peoples' wages stopped dropping. That doesn't hurt the
argument because we still don't know hat would happen now that peoples' wages stopped dropping. Will they spend, will they not spend? Since this doesn't affect
the argument it can't be a necessary assumption of the argument. Just a quick note of
clarification on negation before we move to the next choice. If you negate a choice for a
necessary assumption question and negating that choice
weakens the argument, then you have the answer. What it means is you took away
something that was necessary to the original argument and that's why the argument was weakened. If you negate a choice
and it does nothing to the argument, or it strengthens the argument, then that's not the answer. Think about it this way, let's
say that I believe that water is necessary for a plants' survival. If I wanted to test
whether that's really true, what I would want to do is take water away and see what happens. If that plant is weakened, then yes, water must be necessary. If nothing happens to the plant, then I guess water wasn't
necessary after all because I took water away
and the plant was still okay. So that's the idea
behind testing necessary assumption choices by negating them. And then seeing what the impact is on the argument to do so. Okay, let's move on. D, consumers will be less
reluctant to spend money if income taxes are lowered. This is a match, this is almost
exactly what we predicted. And to test it, let's negate this choice. What if consumers
wouldn't be less reluctant to spend money if income
taxes are lowered. In other words, let's just
say they still don't want to spend money, even though their
income taxes were lowered. In that case, the economist
argument falls apart. Because the lowering of
income taxes wouldn't improve this economy that's weak
because people aren't spending. So choice D is a necessary assumption and we can select it on test day. For the record, E, is
irrelevant to the argument. Because, it focuses on
government spending. Which isn't something the
economist ever addressed. So an idea that's irrelevant
to the argument can't be a necessary assumption,
it can't be the claim that keeps the argument alive. So to recap, for necessary
assumption questions it's helpful if you can
phrase the conclusion and the evidence simply
and accurately on test day. Then you can look for the
gap between the evidence and the conclusion and make a prediction for what must be true but wasn't stated in order for the argument to work. If you wanna test a
choice, you can negate it and see what happens. If negating the choice does
nothing to the original argument or makes it better,
then that choice is wrong. If negating a choice makes
the original argument fall apart, then you've got your answer.