Condition

In logic, a condition is a fact that indicates the truth of another fact. There are two types of conditions: necessary conditions and sufficient conditions. A condition may be:

• Necessary but not sufficient: "Being alive is a necessary but not sufficient condition for breathing. It is necessary to be alive in order to breathe. However, being alive is not proof that one is breathing -- because one can hold one's breath."
• Sufficient but not necessary: "Taking a flight to Europe" is a sufficient condition for "Getting to Europe." If you took a flight to Europe, you got there. However, it is not a necessary condition -- because you might have taken a boat.
• Necessary and sufficient: "Having alleles for brown eyes on both chromosomes is a necessary and sufficient condition of having brown eyes. If you have two brown alleles, you definitely have brown eyes. If you have brown eyes, you definitely have two brown alleles."
• Neither necessary nor sufficient: "Having the flu is neither a necessary nor a sufficient condition for feeling nauseous. You can feel nauseous if you don't have the flu, and you can have the flu without being nauseous."