This dissertation is concerned with identifying fundamental conceptual properties of nouns and verbs. At issue is whether or not the noun and verb categories can be sufficiently captured by the syntactic primitives +N and +V within an autonomous syntactic module. Based on reading response times to verbs and derived nouns (e.g., explode/explosion) and on an analysis of aphasic patients' noun and verb production, I argue that event structure prototypes (e.g., eventive/stative), conceptual archetypes (e.g., figure/ground), metaphor, metonymy, and body-part active zones (e.g., body-parts crucial to or impacted by actions) contribute to the dynamic conceptualization of nouns and verbs. Furthermore, I argue that this evidence supports the hypothesis that prototypes posited for noun and verb categories may be at least partially dependent on the way in which we are "wired" to perceive the world (e.g., Damasio and Tranel's (1993) hypothesis that the ventral and dorsal visual pathways play an important role in the conceptualization of nouns and verbs). The dissertation begins with an intriguing dissociation between nouns and verbs experienced by some aphasic patients - access to words from either category can be selectively impaired as a result of cerebral damage. Chapter 1 provides a brief overview of attempts to characterize noun and verb categories and of research on aphasia. Chapter 2 discusses the noun/verb dissociation in aphasia. Chapter 3 correlates lexical and semantic-conceptual accounts of the dissociation with formal and cognitive linguistic theories of modularity, the lexicon, and grammatical class. Chapters 4 through 6 present evidence from 10 Broca's and 10 Wernicke's patients' responses to noun and verb targets which indicates that semantic-conceptual processing cannot be dissociated from grammatical class effects - the patients' noun and verb target substitutions were primarily motivated by the conceptualization of bodily action, pragmatic knowledge, and event structure archetypes. Chapter 7 extends the argument for the semantic-conceptual basis of noun and verb categories to English nominalizing morphemes. Evidence from a self-paced reading study which contrasts verbs and derived nouns in congruent and incongruent contexts shows that conceptual boundedness (e.g., count/mass, perfective/imperfective) significantly interacts with context and grammatical class. (Margaret Kellogg)