When Would a Conditional Statement Be a Necessary Assumption

[donghai819]

Hi folks,

As many of us have figured, many correct answers of Necessary Assumption family questions are something like: "(at least) some of these folks/animals/stuffs/thoughts would/have/could/did do it/them. So far so good. But I wondered if there is a situation where a conditional statement is required as a necessary assumption rather than sufficient one; that is, it is different from the conditional statement in sufficient assumption questions. If so, could any body elaborate?

I'd like to share one example made up by myself to illustrate my point, in case it is not very clear.

Example: The students who got As in the mid-term are diligent, since every diligent students stayed in the Goodstudent Library during the entire weekend.
So we'd have:
P: diligent student --> stay in library.
C: got As --> diligent.
Sufficient Assumption: every student who got A stayed in the library during the weekend, aka, got A --> stay in library.
One of the Necessary assumptions: every student who got A must not visit their granny during the weekend.

Many thanks in advance!

[maryadkins]

Your example is great. And correct.

I don't think I understand your question, though. In case this is what you're getting at:

Conditional logic (If = Sufficient, Then = Necessary) is different from Necessary and Sufficient Assumption QUESTIONS.

It's confusing because we use the same terms for both, I know. But you want to think of them separately.

1. Conditional logic is a tool you can use on all kinds of LR question types, such as the example you gave in your post. The part that comes after the "if" we refer to as the "sufficient" part of the conditional statement; the part that comes after the "then" we refer to as the "necessary" part of the conditional statement. As you already know, when you have several of these statements with pieces that "match up," you can string them together to make inferences (again, like you did in your example).

2. Assumption questions in Logical Reasoning on the LSAT come in two types: Necessary Assumption questions, and Sufficient Assumption questions. Your task for the former is to find what must be true. Your task for the latter is to make the conclusion true.

Sometimes you'll use conditional logic to do this, like you did in your example. Other times, you won't use conditional logic at all. Think of conditional logic as a fork: it works for some foods but not others.

[MikaylaA752]

When do bridge ideas and defender ideas come into play? Are they a type of necessary assumptions, or a separate question type entirely?

[ohthatpatrick]

Bridge and Defender ideas are concepts that apply to varying degrees to several question types:

Necessary Assumption
Sufficient Assumption
Strengthen
Principle-Strengthen

All of these correct answers share a common quality: they strengthen the argument at least somewhat.

BRIDGE: strengthens an argument by better connecting two ideas that are meant to be connected / equated
DEFENDER: strengthens an argument by ruling out a potential objection

In a technical sense, every assumption Bridge assumption is also a Defender assumption (because if the Bridge idea weren't true, that would be an objection to the argument .... the Bridge idea, then, rules out that potential objection)

But that is unhelpful. The potential value of these terms to me would be this:
BRIDGE: these answer choices connect ideas that have already been mentioned
DEFENDER: these answer choices bring in new concepts that might be relevant to judging the argument

Example:
Maria applied to Notre Dame. Thus, she must want to go to a good school.

BRIDGE ASSUMPTIONS
Notre Dame is a good school
Applying somewhere indicates a desire to go there

DEFENDER ASSUMPTIONS
Maria's Dad did not pressure her into applying
Maria is not just applying to see whether she would be accepted
Maria is not applying to Notre Dame merely because it's the closest school to her house
Maria is not applying because she lost a bet with her friend Dave

Bridge assumptions are very finite, since they're limited by which terms in the argument still need to be connected.
Defender assumptions are potentially infinite, because you can create a Defender assumption by thinking of a possible objection to an argument and then just ruling that out.

Let me pull some percentages out of my gut:

Necessary Assumption - 70% bridge / 30% defender
Sufficient Assumption - 98% bridge / 2% defender
Strengthen - 20% bridge / 20% defender / 60% other ways to strengthen
Principle-Strengthen - 100% bridge