Necessary and Sufficient Causes

    When social scientists speak of causation, as you've seen, they may mean something slightly different from what it meant in ordinary conversation.  In particular, social scientists are more specific and precise in their use of the term.

    Thus a necessary cause is a condition that use be present for the effect to occur.  For example, we might say that gender is a cause of necessary cause of pregnancy in that you must be female in order to become pregnant.  It is not a sufficient cause, however, since you can be female without being pregnant.

    A sufficient cause is a condition that always produces the effect in question.  For example, skipping the final exam in this course would be a sufficient cause of failing it, though it is not a necessary cause: you could fail in other ways.

    In practice most analysis uncover causal relationships that approximate one of the other of these types, but they seldom uncover an absolutely (100%) necessary or sufficient cause.

    The ideal, of course, would be to discover the necessary and sufficient cause of something (e.g., child abuse) but that seldom, if ever, occurs in the social (or other) sciences.