Affixes attach in fixed orders: English prefixes precede the root, and suffixes follow in a predictable sequence (e.g., derivational before inflectional). This order is not random but reflects the structure of word formation: position classes define which affixes can occupy which slots. Violations of canonical affix order are rare and often involve special morphological processes (infixation, circumfixation), suggesting ordering constraints are fundamental to morphological systems.
Collect words with multiple affixes and determine the position class of each. Identify deviations and explain them as special morphological phenomena or exceptions.
From your study of morphological structure, you know that words are built from meaningful units — roots, prefixes, and suffixes — assembled according to systematic rules. But one question morphological structure leaves open is: when a word takes multiple affixes, why do they appear in the order they do? You cannot say *un-kind-ness* and then freely rearrange it as *kind-un-ness* or *ness-un-kind*. The order is fixed, and the study of affix ordering constraints explains why.
The core concept is position class: a slot in the word-template that can be filled by a specific set of affixes. Think of it like a template with numbered positions: [PREFIX-2] [PREFIX-1] [ROOT] [SUFFIX-1] [SUFFIX-2] [SUFFIX-3]. Each position has a defined role, and affixes belong to exactly one position class. In English, derivational affixes (which change a word's category or meaning: *-ness*, *-ful*, *un-*, *re-*) generally appear closer to the root, while inflectional affixes (which mark grammatical relationships: *-s*, *-ed*, *-ing*) appear at the outer edges. So you get *un-kind-ness-es* (prefix + root + derivational suffix + plural), not *un-ness-kind-es*. This isn't a coincidence — it reflects the hierarchical structure of word formation.
Why does derivational morphology sit inside inflectional morphology? The answer connects to the syntax-morphology interface you may have encountered in distributed morphology. Derivational operations are part of building the lexical item itself — changing what the word *is*. Inflectional operations are added later, adjusting the word for its syntactic context (tense, number, agreement). Since syntax operates on fully-formed words, inflectional affixes must be added after the word's core meaning is established. The ordering is therefore not arbitrary: it reflects the sequence of operations in grammar, from lexical construction outward to syntactic deployment.
Violations of canonical affix order are rare but informative. Infixes — affixes inserted inside a root (the English expletive infix in *fan-f\*\*king-tastic*) — appear to break positional rules but in fact follow their own predictable prosodic constraints (they appear before the main-stressed syllable). Circumfixes bracket the root with simultaneous prefix and suffix (*ge-...-t* in German past participles). These exceptional cases confirm the rule by showing that deviations are systematic, not random — they follow alternative morphological processes with their own logic. Whenever affix ordering seems irregular, the linguist's task is to identify which alternative process is operating, not to treat the deviation as an unexplained exception.