This dissertation reconstructs Spinoza's theory of language and explains how different facets-from physiological to semantic-work together to determine language's function.While the Ethics provides the underpinnings for Spinoza's account of the human mind, the TTP illustrates how language functions in a social context.In Chapter 1, I reconstruct Spinoza's theory of language based on his account of the human mind provided in the Ethics. Language has its root in the mind's power of imagination, which is based on a physical-physiological framework that I call the physical-physiological mechanism of language. In Chapter 2, I address how language shapes the way in which individuals interact with each other. This chapter focuses on the communicative function of language in Spinoza's political writings. Language shapes the social life of human beings. In such a way, language constitutes and sustains the ratio by which a State maintains itself as an individual. Chapter 3 stresses language's role in Spinoza's pedagogy. Language, with its communicative and cognitive functions, represents two types of educators: prophets and philosophers. Chapter 4 focuses on Spinoza's employment of the geometrical method as a philosophical language in the Ethics. The geometrical method is a pedagogical tool, a pedagogical tool that addresses language's cognitive function and aims to educate philosophers. Spinoza's use of the geometrical method establishes a semi-artificial language designated for reasoning. With regard to Spinoza's theory of language and pedagogical concerns, I engage in the scholarly debate on the "free man." I propose that the "free man" is a literary persona that aims at the readers' cognitive capacity and serves a pedagogical function.