Principles of categorization: the case of word classes

In the present paper, we present neurocognitive and linguistic data on word class distinction, from both typological and historical perspectives, and show that 1) a superordinate principle of categorization, above the cluster of features defining nouns, verbs and adjectives, functions as an organizing principle of word knowledge in the brain; 2) this principle critically operates in the actualization of grammar, where word class-specific information is crucial to produce and comprehend words in their appropriate context: evidence from neuropsychology and neuroimaging is consistent with results from historical and typological studies on word class distinction; 3) this principle is implemented prototypically: the neural underpinning of word classes reveals the multifactorial and graded nature of categories and, then, parallels typological observations; 4) the combination of neurocognitive evidence with typological and diachronic data makes specific contributions to the debate on the universality of grammatical categories.