This paper focuses on motivating affix subcategorization constraints in order to explain deviant stress patterns caused by affixes. The main idea is that affixes select their prosodic base for affixation. These subcategorization constraints, formulated in Alignment schema, consist of four different types: Align-to-σ', Align-in-σ', Align-to-Ft, and Align-in-Ft. Data from various languages are considered to motivate these constraints. It is shown that these constraints offer systematic explanation to the role of affixes in stress assignment and to apparently deviant stress patterns caused by affixes.