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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