Necessary versus Sufficient Conditions.

**Definition: **A necessary condition for some state of affairs S is a
condition that must be satisfied in order for S to obtain.

*For example, *a necessary condition for getting an A in 341 is that a student
hand in a term paper. This means that if a student does not hand in a term paper, then a
student will not get an A, or, equivalently, if a student gets an A, then a student hands
in a term paper.

**Definition: **A sufficient condition for some state of affairs S is
a condition that, if satisfied, guarantees that S obtains.

*For example, *a sufficient condition for getting an A in 341 is getting an A on
every piece of graded work in the course. This means that if a student gets an A on every
piece of graded work in the course, then the student gets an A.

Handing in a term paper is not a sufficient condition for getting an A in the course. It is possible to hand in a term paper and not to get an A in the course.

Getting an A on every piece of graded work is not a necessary condition for getting an A in the course. It is possible to get an A in the course even though one fails to get an A on some piece of graded work.

In her essay, Mary Anne Warren does not maintain that each of her five conditions is *individually
sufficient *for being a person, though she thinks that some of them may be, and she
thinks that the *conjunction* of the first three (consciousness, reasoning, and
self-motivated activity) is probably sufficient for personhood. This means that she thinks
it is probably true that if anything is conscious, able to reason, and engages in
self-motivated activity, then that thing is a person. She maintains that satisfying
all three of these conditions is sufficient for being a person.

Warren does not argue that any of her five conditions is *individually necessary*.
But she does maintain that the *disjunction* of the five conditions is necessary.
That is, she maintains that a necessary condition for personhood is that something satisfy
*at least one *of these five conditions. In other words, she maintains that if none
of these five conditions is true of something, then that thing is not a person.

Self-Test

T F 1. Being a mammal is a sufficient condition for being human.

T F 2. Being human is a sufficient condition for being a mammal.

T F 3. Being alive is a necessary condition for having a right to life.

T F 4. Being alive is a suffcient condition for having a right to life.

T F 5. If it is true that if P then Q, then P is a sufficient condition for Q.

T F 6. If it is true that if P then Q, then Q is a necessary condition for P.

T F 7. If it is true that if P is not the case, then Q is not the case, then P is a necessary condition for Q.

T F 8. If it is true that if P is not the case, then Q is not the case, then P is a sufficient condition for Q.

T F 9. Something is a brother if and only if it is a male sibling. This means that being a male sibling is both necessary and sufficient for something to be a brother.

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