Rickooreo
KarishmaB egmat ReedArnoldMPREP MartyTargetTestPrep Is there any concept notes/ video I can refer to to improve accuracy on necessary and sufficient condition
Hi Rickooreo,
Here is a link to an LSAT video MPrep did on 'necessary' vs 'sufficient'
The basic gist is:
A sufficient condition *guarantees* a conclusion is true. But if it's false a conclusion could still be a true.
A necessary condition is *required* for a conclusion to be true. But if it's true the conclusion could still be false.
For instance, "My dog has plenty of food in his bowl, so he'll probably be able to live for the next month while I'm on vacation."
Well, hold on. Food is a *necessary* condition for survival, but not *sufficient.* True, if my dog does not have food, it won't survive, but, just giving it food doesn't guarantee the conclusion. Will my dog have access to *water?* That is also a necessary condition for survival. Will my dog have access to oxygen? That's also necessary for survival. None of these alone is sufficient, but each one is necessary.
"This animal is dog, so it must be mammal." Well, dogs are mammals, by definition. So knowing an animal is a dog is *sufficient* to know it is a mammal. If it's not a dog, does that mean the conclusion is *wrong?* No... The animal could be some other kind of mammal. But knowing it is a dog is sufficient to know it's a mammal.
And sometimes you have things that are necessary AND sufficient. "The door is not closed, so it must be open." Knowing a door is not closed is SUFFICIENT to show that the door is open, but it's also NECESSARY for the door to be open. If you know the door is not closed, you know it's open, and in order for a door to be open, it is required that it not be closed.
However, note that this isn't *hugely* important on the GMAT... Most of what you need to consider on the GMAT is *necessary* conditions. You'll need to wonder about what things need to be true for a conclusion to hold, not what things *prove* an argument.
So here's a quasi-realistic example: "The restaurant raised its prices on all its sandwiches, and sold more sandwiches, so it must have made more profit on its sandwich sales."
You might be aware that 'costs' are glaringly missing from this argument. Well, on the GMAT, it's almost always more useful to think about the NECESSARY assumption: "Costs didn't increase too much to cancel out their revenue increase" than to think about the SUFFICIENT assumption: "Costs didn't increase."
We know they have more revenue, because they raised price and sold more. If we KNOW costs didn't increase AT ALL, well, the argument is GUARANTEED. But if costs go up it doesn't RUIN the argument, they just can't go up TOO MUCH. It's NECESSARY that costs didn't increase more than the revenue did. If costs *did* increase that much, than the conclusion falls apart. The GMAT is almost always more interested in the necessary condition. If a question asked, "Which of the following is an assumption required by the argument?" A very tempting trap answer would be "The costs of the sandwiches for the store did not increase," because that isn't *actually* required.