Task Predecessors is a term which is used in project planning, particularly in Critical Path Method (CPM). Conception of task predecessors is based upon the fact that usually there are some tasks in a project plan, which cannot be started or finished until certain previous tasks are completed: these tasks (allowing starting or completing the next tasks) are called predecessors, while their dependent tasks are called successors.
Start or finish dates of task predecessors determine the start or finish dates of their successor tasks. In other words: there are always some tasks on the project schedule, which have their start or finish dates being driven by these dates of their predecessors. Defining predecessors for every task on the project is an indispensable part of building a project’s WBS and Critical Path; it includes defining a task dependency – how the linked tasks relate in terms of their finish and start dates. There are four kinds of task dependencies: