Lexicalist Hypothesis

The Lexicalist Hypothesis is a hypothesis which entails that syntactic transformations operate on syntactic constituents only, and can only insert or delete designated elements. This means that transformations cannot be used to insert, delete, permute, or substitute subparts of words. The lexicalist hypothesis comes in two versions: (a) a weak version which says that transformations cannot be used in derivational morphology (= Weak Lexicalist Hypothesis), and (b) a strong version which says that transformations can also not be used in the domain of inflection (= Strong Lexicalist Hypothesis). Recently, the lexicalist hypothesis has been challenged by Baker's (1988) syntactic incorporation hypothesis.

Link
Utrecht Lexicon of Linguistics

Other languages
German Lexikalistische Hypothese