This book is comprised of two parts. The first four chapters concentrate on the metaphysics of substance, while the last two address Spinoza’s metaphysics of thought. These two parts are closely connected, and several crucial claims in the last two chapters rely on arguments advanced in the first four. I intentionally use the term ‘metaphysics of thought’ rather than ‘philosophy of mind’ for two main reasons. First, the domain of thought in Spinoza is far more extensive than anything associated with human minds, as will become clear by the end of the work. Second, my primary interest in the last two chapters will be in the ontology of thought in Spinoza, rather than in the kinds of questions we associate with the philosophy of mind. ...