Pronouns are classified as closed-class functional grammatical morphemes (or closed-class words) whose primary role is grammatical coordination and indexing rather than bearing descriptive lexical semantic content, making this statement a foundational linguistic definition.
The claim states a standard linguistic definition regarding the closed-class/functional nature of pronouns versus open-class lexical items. None of the retrieved papers specifically test or dispute this foundational classification; instead, they focus on clinical, computational, or neuro-cognitive processing aspects of language (e.g., connected speech, ERPs, event-related potentials in sentence processing). Because this is a matter of definitional terminology and standard grammatical categorization rather than an empirical discovery currently undergoing scientific debate, it falls under common knowledge/linguistic definition.