Necessary and Sufficient Conditions

Necessary Conditions:
If P is necessary for Q, then Q cannot be true unless P is true.

In other words:
Q is true only if P is true.
"P is necessary for Q because P being true is needed for Q to be true."

For example, what is necessary to get into a university.

1. You must be a human being (a bug can't get into a university)
2. You must submit an application (without an application, you can't get in)
3. Having decent grades (if you're a dummy then you won't get in)

Another example, what is necessary to win the Powerball

1. You must buy a ticket (without a ticket you can't win because you have no chance)

Necessary conditions represent things that must be in place for a certain outcome to occur but in and of itself does not guarantee that certain outcome. If that desired outcome occurs, however, the necessary condition was first met.


Sufficient Conditions:
If P is sufficient for Q, then P's being true is enough to make Q true.

In other words:
If P is true then Q is true.
"P is sufficient for Q because is P is all you need to get Q, P is enough to get Q."

For example, what is a sufficient condition to get into a university.

1. You are a super smart whiz kid who won the Nobel Peace Prize (the university wants you then)
2. You are the No. 1 athlete in the world (the university wants you then)

Another example, what is sufficient to have make the sidewalks get wet?

Rain - if it rains then it guarantees that the sidewalk will get wet. Of course there are other things that can cause the sidewalk to get wet (sprinkler system, water balloon, etc.) but just as long as there is rain that's enough to say that the sidewalk is going to get wet.


Something that is Necessary but not Sufficient: Steering a Car Well
1. Steering a car well is necessary for driving a car well. However, it is not sufficient for driving well. What if you steer like a boss but drive through a stop sign without obeying it?

Something that is Sufficient but not Necessary: Boiling a Potato
1. Boiling a potato is sufficient for cooking it. However, it is not necessary for cooking it as there are other ways in which you can cook a potato (microwave it, bake it in the oven, etc.)