Necessary and Sufficient Conditions

In the social sciences, precise causal relationships are almost never found. That is, we can rarely, if ever, say: If A(and only A) then B (e.g., If employment rises to 20 percent, then the Democratic party will defeat the Republican party). When such a situation exists, however, we can say that A is both a necessary and sufficient condition for B (which is the same as saying that we have, in effect, found the one and only cause of B).