Change Driver: Actor or Document?

Bob Martin’s Single Responsibility Principle, in its Clean Architecture formulation, takes the actor as its primitive: a reason to change is a person who requires changes. The Independent Variation Principle takes the document as its primitive: a change driver is an equivalence class of co-varying domain conditions anchored in a documentable artifact. Which is correct? An actor is a conduit — a person detects a domain change and articulates it. A document is the anchor — it records the domain condition itself. This paper proves that document-based partitioning costs no more than actor-based partitioning under any linear costmodel 𝛼 ⋅ edges + 𝛽 ⋅ contam that prices contaminated co-location at least at the inter-module coordination rate (𝛽 ≥ 𝛼). Contamination is measured relative to document-set equality. Strict superiority holds whenever a dependency edgejoins elements that share a document set but serve different actor sets. When contamination is priced strictly above coordination, it also holds whenever a dependency edge joins elements that share an actor set but are governed bydifferent document sets.