# Confuses sufficient and necessary conditions

• August 18, 2016 at 10:15 am #2438
cecily
Participant

I’m having a lot of trouble with answer choices that have some variation of this answer:

PT 66, section 2, number 11. confuses… “a condition necessary for a phenomenon and one that is sufficient to it.”

I often find it hard to figure out what this means when applied to the question. Is there an easier way to attack questions that have answers like this, and the reverse–which I guess would be confusing sufficient with necessary (or is that the same?).

I’ve read the chapters on it and the wording of this and its implications still really confuse me. If anyone has any insight on an easier way to approach this I would really appreciate any help! Thanks!

• August 18, 2016 at 10:24 am #2440
LSAT Dan
Participant

Hi, Cecily. You probably know that you can’t just switch the order of the terms in a conditional statement. For instance, you can’t go from “If Fluffy is a cat, then Fluffy is a mammal” to “If Fluffy is a mammal, then Fluffy is a cat.” That’s often called a “mistaken reversal.” The second statement is the converse of the first, and a conditional statement doesn’t imply that its converse is true.

Or, in symbolic terms:

P –> Q doesn’t mean that
Q –> P.

When you see this answer choice, what’s going on is basically that the premises gave you a conditional statement, but the conclusion is based on its converse (or inverse, the “mistaken negation,” which is logically equivalent to the converse).

For example, here’s a simple argument where an answer choice like this would be right:

“In order to become an attorney, one must pass the bar exam. Maria passed the bar exam; therefore, she is an attorney.”

The premise gave us this:

A –> PB (necessary condition on the right side of the arrow when neither term is negated)

The conclusion, as applied to Maria, is based on this:

PB –> A

The premise, which always has to be accepted as true, is that passing the bar is a NECESSARY condition for becoming an attorney. The conclusion treats is as a SUFFICIENT condition, i.e. a condition that guarantees that anyone who accomplishes it becomes an attorney. That’s not true. There’s also a background check. There are also bar dues that have to be paid. etc.

Hope this helps.

• August 19, 2016 at 6:08 pm #2447
cecily
Participant

Yes that helps so much! So just to clarify, the correct answer to that problem would be like the argument confuses sufficient for necessary?

• August 20, 2016 at 10:01 am #2450
LSAT Dan
Participant

Yes, or some variation of that. Sometimes it will say something like “takes a event which is required for a situation will arise (i.e. necessary) to be an event that guarantees that situation will arise (i.e, sufficient). You have to parse out the wording; it’s not always identical. But that’s the type of situation that leads to answer choices like that being correct.

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