In logic, the words necessary and sufficient describe the relationship that two propositions or state of things hold, if one is conditioning of the other, cause / effect. Eight kinds of relationships are differentiated.

The first is the necessary condition, which is that the effect can only occur if this condition is one of its causes.

The second is the sufficient condition, which is that which, as soon as it arises, gives rise to the effect.

The third, a condition is said to be necessary and sufficient when both characteristics are given, that is, it is necessary, so that for the effect to occur, it must be one of its causes, and it is sufficient, because given that cause, the effect occurs.

The fourth, it is said that a condition is not necessary, if its concurrence is not essential.

The fifth, it is said that a condition is not enough, if giving does not have to produce the effect.

The sixth, it is said that a condition is necessary but not sufficient, if only arising the cause the effect can occur, but the concurrence of more conditions is necessary.

The seventh, it is said that a condition is sufficient but not necessary, when the effect takes place, although the effect can be given by other different conditions and without its help.

And the eighth, those conditions that are neither necessary nor sufficient, that is, do not relate to the effect.

Everything that exists is classified according to conditionality in two:

1. What is conditioned and we call it Samsara, and
2. what is not conditioned, and we call it Nibbāna.

Everything in Samsara is conditioned, both causes and effects and is what we call kamma.

And, therefore, everything in Samsara can be classified according to the eight previous categories.

Examples:

1. Being born is a necessary condition to get sick: if you are not born you can not get sick.
2. Crashing in an airplane is a sufficient condition to die,
3. Being born is a necessary and sufficient condition to die: if you are born, you die and you can not die if you have not been born.
4. Crashing in an airplane is not a necessary condition to die: you can die in many other ways that are not related to airplanes.
5. Buying a plane ticket is not a sufficient condition for a plane trip.
6. Buying a plane ticket is necessary to fly by plane, but it is not enough.
7. Crashing in an airplane is a sufficient condition to die, but it is not necessary because you can die in other ways.
8. Buying a plane ticket is not a necessary or sufficient condition for it to rain.

Only eight categories relate all of Samsara.