Necessary conditions help to unravel the complexity of social phenomena. When many factors contribute to social outcomes (“multicausality”), some factors are more important than others. Necessary conditions are extremely important: they must be present. If the necessary condition is not present, the outcome will not occur. Necessary conditions are essential, critical, crucial, vital, and cannot be replaced by other factors. Other factors cannot compensate for the absence of the necessary condition. Therefore the necessary condition operates in isolation from other factors. Necessary condition models can be parsimonious: simple, but also rigorous and relevant. 

Necessary conditions are necessary, but not sufficient. A necessary condition allows the outcome to exist, but does not (automatically) produce it. Examples include:

• A high GMAT score is necessary (but not sufficient) for admission to a PhD-program
• HIV is necessary (but not sufficient) for AIDS
• Intelligence is necessary (but not sufficient) for creativity
• Management commitment is necessary (but not sufficient) for successful organisational change
• Contracts and trust are both necessary (but not sufficient) for successful buyer-supplier relations