This approach, he argued, has failed to give us any real understanding of the necessary and sufficient conditions for knowledge.

The following sufficient (but not necessary) condition is often useful.

Continuity is, therefore, a sufficient condition, but not a necessary one.

Consistency is indeed a necessary but not a sufficient condition.

Love is not a sufficient condition for a happy marriage.

It is what philosophers would call a necessary but not sufficient condition.

"They do have a great machine, which is a necessary but not sufficient condition for success."

This is a necessary but not a sufficient condition for successful economic calculation.

In the first two cases, being open or closed is merely a sufficient condition for the result to follow.

But this is only a sufficient condition and leaves open the major question we pose in the next section.