Morphotactics
Morphotactics represent the ordering restrictions in place on the ordering of morphemes. Etymologically, it can be translated as "the set of rules that define how morphemes can touch each other".
Example of a morphotactic rule
Many English affixes may only be attached directly to morphemes with particular parts of speech:- do + -able + -ity = doability
- do + -ity + -able = *doityable