I compare and contrast the properties of uninflecting words such as almost, and uninflectable words such as the indeclinable Russian noun kenguru ‘kangaroo’ or the German adjective rosa ‘pink’, which behave like ordinary nouns/adjectives syntactically, but lack the expected inflectional forms. I relate such lexically uninflectable lexemes to the case of inflectable lexemes in constructions which do not permit inflected forms, such as the noun-head noun position in English N-N compounds, or the German predicative adjective (constructional uninflectability). Uninflecting words raise the question of what it is exactly that gets lexically inserted into syntactic representations. I provide a uniform solution to all these questions by appealing to Stump's distinction between content and form paradigms. Uninflecting lexemes have neither type of paradigm; uninflectable lexemes have a content but no form paradigm; construction uninflectability specifies that both content and form paradigms are bypassed. Lexical insertion of a lexeme lacking, or constructionally deprived of, a form paradigm is defined by a maximally general Default Exponence Principle: 'use the root form'. This approach solves all the descriptive and conceptual problems outlined above.