A necessary precondition is something that must be true prior to something else. Thus, for apples to fall from trees, there must be some force that we call gravity pulling them down. Gravity is here a necessary precondition. But for a particular apple to fall from a particular tree at a particular time, there has to be a particular cause—say, the farmer shaking the tree or a bird pecking at the apple’s stalk. In these latter cases, we have sufficient preconditions. These explain the particularities of a specific incident of an apple falling.
