Dependency Determination: Mandatory, Discretionary, External for PMP

Understanding How Activities Connect

Dependency determination is a critical aspect of the Sequence Activities process in schedule management. Every project schedule is built on dependencies — relationships between activities that determine the order of work. The PMP exam tests your ability to classify dependencies correctly and understand their implications for schedule flexibility and risk.

PMI categorizes dependencies along two dimensions: the nature of the dependency (mandatory vs. discretionary) and its source (internal vs. external). These dimensions combine to create four dependency types that every PMP candidate must master.

Mandatory Dependencies (Hard Logic)

Mandatory dependencies are inherent in the nature of the work. They cannot be changed without fundamentally altering the project approach. These are also called hard logic because they represent fixed, non-negotiable relationships.

Examples:

• The foundation must be poured before the walls can be built (physical constraint)
• Software must be coded before it can be tested (logical sequence)
• Regulatory approval must be obtained before the product can be marketed (legal requirement)

On the exam, mandatory dependencies are identified by language like "must," "required by nature of the work," "physically impossible otherwise," or "legally mandated."

Discretionary Dependencies (Soft Logic)

Discretionary dependencies are established by the project team based on best practices, preferences, or lessons learned. They could be changed if needed, though doing so carries risk. These are also called soft logic, preferred logic, or preferential logic.

Examples:

• Completing the design document before starting development (best practice, but some overlap is possible)
• Finishing module A before starting module B (preferred sequence, but parallel development is feasible)
• Conducting user acceptance testing after system testing (common practice, but could be adjusted)

Discretionary dependencies are important for the exam because they represent schedule flexibility. When a project needs to compress its schedule through fast-tracking, discretionary dependencies are the candidates for modification — mandatory dependencies cannot be changed.

External Dependencies

External dependencies involve relationships between project activities and activities outside the project's control. They represent factors that the project team cannot influence.

Examples:

• Government permit approval before construction can begin
• Vendor delivery of hardware before installation can start
• Another project completing a shared platform before this project can integrate

External dependencies are significant risk sources because the project team has limited ability to expedite or control them. The PMP exam may test whether you recognize external dependencies and their risk implications.

Internal Dependencies

Internal dependencies involve relationships between activities within the project team's control. They represent sequences the project team manages directly.

Examples:

• The project team must complete requirements before beginning design
• Internal testing must finish before the team delivers to the client
• Training materials must be developed before trainer certification begins

Internal dependencies are generally more manageable than external ones because the project team can adjust resource allocation, work sequences, and priorities.

The Four Combinations

The two dimensions combine into four dependency types. Understanding each combination strengthens your exam performance:

1. Mandatory Internal — Inherent in the work, within the team's scope. (Foundation before walls on a team-built structure.)
2. Mandatory External — Inherent in the work, outside the team's control. (Regulatory approval before market launch.)
3. Discretionary Internal — Preferred by the team, within the team's scope. (Sequential testing phases that could overlap.)
4. Discretionary External — Based on industry practice, involving external parties. (Following a vendor's recommended implementation sequence.)

Dependencies and Schedule Compression

Understanding dependency types directly affects schedule compression strategies:

• Fast-tracking involves performing activities in parallel that were originally planned sequentially. Only activities with discretionary dependencies can be fast-tracked. Fast-tracking mandatory dependencies is either impossible or extremely risky.
• Crashing adds resources to shorten activity durations. It does not change dependencies but increases cost. Crashing is applied to critical path activities regardless of dependency type.

When the exam describes a schedule compression scenario, identify the dependency type before choosing your answer. Fast-tracking a mandatory dependency is a trap answer.

Exam Tips

1. Look for keywords: "must" and "required" signal mandatory; "preferred" and "best practice" signal discretionary
2. External dependencies = risk. If the scenario involves waiting for an external party, assess risk implications.
3. Discretionary dependencies = flexibility. If the project needs to compress the schedule, discretionary dependencies are the levers.
4. All four combinations are testable. Do not assume that all mandatory dependencies are external or that all discretionary dependencies are internal.

Practice identifying dependency types in scheduling scenarios on PMPprep. Our scheduling cheat sheets include a dependency classification quick-reference that helps build pattern recognition for exam day.