The phrase early state date refers to the specific point on the critical path method which represents the earliest possible point at which the as yet to be completed segments of a specific schedule activity or the project in general can begin. The determination of this particular early state date is dependent on a number of variables. These variables include the determined data date, all factors relating to the schedule network logic, as well as any particular schedule restraints that have been determined to be a factor for consideration. It is important to keep in mind that these early start dates are not set in stone and can in fact change as the situation dictates. For example, during the progression if the project, the project could fall behind or move ahead of schedule, which could ultimately lead to a modification of the project management plan. This could result in modifying the early start date.
This term is defined in the 3rd and the 4th edition of the PMBOK.