B.1.5.RS:10 - Architectural Rationale

Substitution is a relation to a receiving use. A constituent’s attractive property does not establish that relation. Recovering the whole’s dependence avoids both unrestricted replacement and unnecessary preservation of detail.

When the receiving uses are already understood, the practitioner can begin with their requirements and compare the replacement directly. The result is a directed substitution decision across one or several uses, including a candidate that changes the whole to accommodate the new constituent.