The Union of Thought and Being in Spinoza

I propose a new understanding of the relationship between thought and being in Spinoza, according to which each idea in God's intellect is united---but not identical---to its object. This interpretation resolves a longstanding tension in Spinoza scholarship concerning whether he is an idealist. On the one hand, it seems that Spinoza could not have endorsed idealism, since he straightforwardly affirms the reality of extended things. On the other hand, when explicating some of the most fundamental commitments of his ontology, he places mental relations front and center. To resolve this tension, I offer a complete reconceiving of three such appeals to mental relations, as they are found in his parallelism doctrine, theory of the mind-body relation, and theory of attributes. The result is not only a positive understanding of the relationship between thought and being in terms of a union, but also a new explanation of why Spinoza cannot be an idealist.;I begin with a reinterpretation of the so-called parallelism doctrine, where Spinoza tells us that the causal orders of thinking and extended things are "one and the same." It is in this context that we also learn that extended things and their ideas in God's intellect are "one and the same thing." Since, for Spinoza, the mind is the idea of the body, he is thus standardly thought to be a precursor of contemporary defenders of the mind-body identity thesis. But I argue that "one and the same" has been misinterpreted: it does not mean that the causal orders of thinking and extended things are in any sense "parallel," nor that ideas and their objects (e.g., mind and body) are identical.;Accordingly, I provide a new account of the nature and scope of the relation picked out by "one and the same." Regarding its nature, both Descartes and Spinoza sometimes use "one and the same" to indicate that two things are non-identical but united. Strikingly, Descartes says that mind and body are "one and the same" because they are united in the same human being. Spinoza seems to agree with Descartes on this much, given Spinoza's explicit endorsement of a "union" of mind and body. However, while Descartes regards mind and body as separable, Spinoza maintains that they are inseparable. Ultimately, I argue that, for Spinoza, the relation picked out by "one and the same" consists in the fact that two things (e.g., mind and body) are essential features of some further thing (e.g., the human being). With regard to the scope of this relation, most interpreters do not hold that all ideas are one and the same thing as their objects, the main exception being the idea of God. However, I argue that this exception is ad hoc, and ultimately motivated by the reading of "one and the same" in terms of numerical identity. With the help of this widening of scope, I argue that the entire causal orders of thinking and extended things are "one and the same" in the sense that they are united.;I then offer a new explanation of Spinoza's notorious definition of 'attribute' as "what the intellect perceives of a substance, as constituting its essence." Since the attributes (such as thought and extension) really do constitute the essence of substance, what role are the intellect and its perceptions serving in this definition? I propose that the answer to this puzzle lies not in any latent idealism in Spinoza, but rather in how Spinoza uses the term "attribute": it can refer to things which exist outside the intellect, such as thought and extension, or to things which exist in the intellect, such as the perceptions or ideas of thought and extension.;Finally, I argue that the foregoing interpretations of "one and the same" and the theory of attributes jointly provide a new, compelling explanation of why Spinoza cannot be an idealist, as well as why his metaphysics is not laced with intensionality. In this vein, I consider other sources of intensional and idealist readings of Spinoza, such as his mysterious "expression" relation, and argue that these further themes can now more easily be accounted for on alternative grounds. I conclude that Spinoza's positive theory of the relationship between thought and being is that they are united.