LSAT Logic | Sufficient vs Necessary Conditions

We deal with “if-then” statements all the time in everyday life. “If I have another drink or two, I won’t be able to drive safely.” “If I get a higher LSAT score, I’ll be competitive at better law schools.”

The LSAT Logical Reasoning section requires us to think about these statements a little more formally than we’re used to. (If we want to do well on the LSAT’s Logical Reasoning section, we’ll have to think about these statements more formally.)

This article will explain “sufficient” and “necessary” and describe them with a few examples.

The “sufficient” condition is often introduced by words such as “if,” “when,” and “whenever.”

Something that’s sufficient is enough to get the job done. However, without more info, we can’t assume that it’s a requirement (necessary).

It might help to think of the sufficient condition as “activating” the necessary condition.

The “necessary” condition is often introduced by words such as “then,” “must,” and “required.”

Something that’s necessary has to happen in order for the “sufficient condition” to occur.

However, without more info, we can’t assume that it’s the only thing that has to happen in order to know that the sufficient condition also happened (or will happen).

Here are a few examples of the sufficient and necessary conditions in action:

Limos

“If I take a limo, I’ll get where I want to go.”

A limo would be sufficient to get me wherever I want to go.

However, I don’t need fancy forms of transportation. There are other ways to get to where I need to go – I could walk, run, bike, or take the subway, bus, or a taxi.

(In fact, I’d prefer a helicopter or rocket ship over a limo if I had my pick.)

Un-friending on Facebook

“If we break up, I’ll un-friend him/her on Facebook.”

Breaking up might be sufficient to un-friend a significant other, but breaking up isn’t required (necessary) to un-friend him/her.

You might un-friend him/her in the middle of a fight without actually breaking up.

Becoming President

“If you have a reasonable chance of becoming President of the United States, then you must be affiliated with one of the two major political parties.”

However, being affiliated with the Democrats or Republicans is not enough to become President. You also need to win your party’s nomination and, eventually, the Electoral College.