The critical path, as defined by academia, is known as the longest and the shortest, i.e. the longest path through the network but the shortest amount of time in which the project can be completed as shown for Tasks 6-8 in the following illustration:

If, however, there is a need to review the critical nature of each individual network, an option can be selected to display multiple critical paths as shown in the following illustration:

Once Calculate multiple critical paths is selected, the critical nature of each independent network will be displayed as shown in the following illustration:

Now, what would happen if a Start No Earlier Than constraint is applied to Task 11 of October 1, 2020? The answer: within the independent network of Tasks 9-12, Tasks 9-10 will not be critical as each task will have 1 day of Total Slack, and Tasks 11-12 will remain critical as each task will continue to have 0 days of Total Slack within the independent network as shown in the following illustration:

And now, if the option to display multiple critical paths is deselected, only one critical path is displayed as shown in the following illustration:

Applies To: All Current Versions of Microsoft Project.