September 8, 2026 · 7 min read
TL;DR: Dependency options are keyed 6 times and offered as distractors 15 times in this bank, and the misses cluster on one habit: answering half the question. A dependency carries two independent attributes, the logical relationship (finish-to-start, start-to-start, finish-to-finish, start-to-finish) and its nature (mandatory, discretionary, external, internal). The exam asks about both, sometimes in the same item, and picking the right relationship with the wrong nature scores nothing.
Candidates memorise the four relationship types and stop there. The bank's distractors are built on the assumption that they stopped there.
First, which end of each activity is tied to which. Second, why the tie exists at all.
The bank has an item that asks both at once. A task is 90% complete but cannot finish until another task finishes first, and the question says choose 2. The keyed pair is finish-to-finish and mandatory dependency. The explanation separates the two answers cleanly: because the first task cannot finish until the second finishes, the logical relationship is finish-to-finish, and since the relationship is required rather than chosen for convenience, it is also a mandatory dependency. Finish-to-start and discretionary dependency are the two distractors, one from each axis.
That structure is worth internalising. When a stem describes a dependency, work out the relationship from the verbs (which activity's start or finish is being constrained) and the nature from the cause (is the sequence a fact about the work, a choice by the team, or something outside the project).
| Attribute | Options | What decides it |
|---|---|---|
| Logical relationship | FS, SS, FF, SF | Which end of the predecessor constrains which end of the successor |
| Nature | Mandatory, discretionary | Whether the sequence is inherent in the work or chosen |
| Source | Internal, external | Whether the project team controls the constrained activity |
Read for what is being constrained, not for what sounds familiar.
Finish-to-finish, disguised as parallel work. A product owner wants the next feature pulled forward to run in parallel with the current one, and the dependency means the new feature cannot finish until the current one finishes, but both can be worked at the same time. Keyed is changing the dependency to finish-to-finish. The explanation names why this is precisely a finish-to-finish relationship: the successor's finish is constrained by the predecessor's finish and nothing constrains its start, which is what allows parallel working while keeping the delivery order intact. Finish-to-start is called out as the closest miss and is also the default relationship, which is exactly why it is the tempting wrong answer.
Finish-to-start with a lag. Equipment installation can begin 15 days after the equipment foundation is completed. Keyed is finish-to-start with a 15-day lag. Three distractors sit around it, and each swaps one attribute: finish-to-start with a lead, start-to-finish with a lead, and finish-to-finish with a lag. The relationship is finish-to-start because installation can start only after the foundation is finished, and the 15 days is a lag because it is waiting time inserted before the successor may begin.
Start-to-finish, the rare one. A question asks which of the four relationships is used least often. Keyed is start-to-finish, and the explanation is the clearest statement of it in the bank: a successor activity cannot finish until its predecessor has started, turning up mainly in handover situations, where the incoming shift is the predecessor whose start is what finally releases the outgoing shift, the successor, to finish. If you have struggled to hold start-to-finish in your head, the shift-handover picture is the one to keep.
External, and therefore not yours. A pharmaceutical plant requires government hearings about the end product before site preparation can begin. Keyed is external dependency, because it ties a project activity to a non-project activity the team does not control. Mandatory and discretionary are both offered, and this is where the two axes get confused: the hearings genuinely are mandatory in the everyday sense, but the question is asking about source, and the defining feature is that the constraining activity sits outside the project.
Because it decides what you are allowed to change.
The bank puts this to work in a schedule-compression item. A project is three weeks behind and must be compressed, there is not enough budget to crash, and the project manager checks with each area lead about fast-tracking. The question asks which dependencies to fast-track. Keyed is the discretionary ones, and the explanation gives the rule in full: fast-tracking runs activities in parallel that were planned in sequence, so it is only available where the sequence was a choice rather than a fact. A discretionary dependency is preferred logic, adopted because it reflects best practice or the team's habitual way of working, which means the project that imposed it can also relax it, at the cost of the rework risk that makes fast-tracking a trade rather than a free gain. A mandatory dependency is inherent in the work itself, and the explanation reaches for the standard example: concrete cures before load is applied.
External dependencies and mandatory dependencies are both offered as distractors here, and both fail for the same reason. Neither is yours to relax.
Common trap: treating "mandatory" as a description of how important something is. In this bank, mandatory means the sequence is a property of the work, not that somebody insisted on it or that a regulation demands it. A regulator's hearing is an external dependency even though missing it would stop the project cold, and a team's habit of writing all the documentation before starting the next module is discretionary even if the team believes it is non-negotiable. The bank flags this distinction by name in its explanations rather than just marking the option wrong, and it is what makes the fast-tracking question answerable at all: importance would not narrow the field, but who owns the sequence does.
What are the four dependency relationship types? Finish-to-start, start-to-start, finish-to-finish, and start-to-finish. Finish-to-start is the default in most schedules. Start-to-start and finish-to-finish are common wherever activities are deliberately overlapped. Start-to-finish is the rare one and turns up mainly in handover situations.
What is the difference between a mandatory and a discretionary dependency? A mandatory dependency is inherent in the work itself, for example concrete must cure before load is applied. A discretionary dependency is preferred logic, adopted because it reflects best practice or the team's habitual way of working, which means the project that imposed it can also relax it.
Which dependencies can you fast-track? Discretionary ones. Fast-tracking runs activities in parallel that were planned in sequence, so it is only available where the sequence was a choice rather than a fact. Fast-tracking a mandatory dependency is not an option, because the sequence is a property of the work.
What is the difference between a lead and a lag? A lag is waiting time inserted between activities, so the successor starts later than the relationship alone would allow. A lead lets the successor start earlier, overlapping the predecessor. If a stem says work can begin a number of days after something finishes, that is a finish-to-start relationship with a lag.
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Related reading: Critical Path Method (CPM) & Float and Crashing and Fast-Tracking: 4 Keyed, 22 Distractors, and One Question Settles It. Schedule tasks are mapped on the Process domain study page.
What are the four dependency relationship types?
Finish-to-start, start-to-start, finish-to-finish, and start-to-finish. Finish-to-start is the default in most schedules. Start-to-start and finish-to-finish are common wherever activities are deliberately overlapped. Start-to-finish is the rare one and turns up mainly in handover situations.
What is the difference between a mandatory and a discretionary dependency?
A mandatory dependency is inherent in the work itself, for example concrete must cure before load is applied. A discretionary dependency is preferred logic, adopted because it reflects best practice or the team's habitual way of working, which means the project that imposed it can also relax it.
Which dependencies can you fast-track?
Discretionary ones. Fast-tracking runs activities in parallel that were planned in sequence, so it is only available where the sequence was a choice rather than a fact. Fast-tracking a mandatory dependency is not an option, because the sequence is a property of the work.
What is the difference between a lead and a lag?
A lag is waiting time inserted between activities, so the successor starts later than the relationship alone would allow. A lead lets the successor start earlier, overlapping the predecessor. If a stem says work can begin a number of days after something finishes, that is a finish-to-start relationship with a lag.