Spinoza’s naturalism comprises a theory of causation and a theory of explanation: things are explained by their causes, and causation itself, ultimately, by the cause of causes, which acts according to a universal and homogenous lawfulness permeating the whole of reality. In Spinoza, the cause of causes, origin and ground of all reality is the substantia infinita, causa sui, natura naturans, which exists and acts from the necessity of its nature alone and compelled by no other thing, and is conceived through itself alone. From the substantia infinita all things follow with necessity, since everything besides substance, being in another and from another, depends for its being and conception on substance. Spinoza’s naturalism is thus of a specific kind.Grounded in a nature which differs with respect to its own cause or source utterly from the nature of individual things, this naturalism determines things to be and act with absolute necessity. Yet the absolutely infinite being, as that which exists and acts ex sola suae naturae necessitate, is the only thing that can be called “free” in a proper sense, whereas everything else, insofar as it is caused by another, is and exists in another, is conceived through another – is determined or compelled by another to exist and act in a particular way – and not by its nature alone. Spinoza’s descriptive and explanatory naturalism is nonetheless tied to a theory of human virtue and happiness which must in important repects be termed intellectualist. For it is the satisfaction of the mind, according to the Ethics, which leads to human freedom and happiness. The satisfaction of the mind, however, lies in the attainment of virtue: the power of the intellect with regard to the affects, a power comprised by adequate knowledge of things, in particular of the affects and their true causes, to which without such knowledge we live in bondage.Spinoza’s Ethics is thus from the outset defined by a fundamental paradox: the paradox of the unity and opposition of freedom and necessity, both of the absolute freedom and necessity of the substantia infinita and of the specific type of freedom and necessity which may be attributed to human beings, their behaviour and actions. This paradox.is rooted in a complex understanding of causality: the infinite, necessary and free, immediate or proximate, immanent and efficient causality of the substantia infinita with respect to the entirety of being in all its manifestations: attributes, infinite modes, particular things ; and the determined, but in some respect potentially free causality of individual human beings. The same paradox is at the root of Plato’s treatment of virtue, as formulated in the famed Socratic paradoxes, and their account of the relationship of knowledge and arete, nature and virtue. A comparison of the Socratic paradoxes can thus help us in sorting out the corresponding relationships in Spinoza’s Ethics and in understanding how Spinoza’s naturalism is related to his intellectualism with regard to his theory of freedom and happiness. Consideration of certain aspects of Aristotle’s formulation of these relationships as contained in psychology, especially his characterisation of the relationship of motivation and knowledge with respect to virtue, may also help to shed light on Spinoza’s apparent aim of synthesizing a naturalist theory of motivation with an intellectualist theory of virtue. The relationship of necessity and free will proves to be intimately connected to this aim. The foundation for the conjunction of naturalism and intellectualism centers meanwhile on certain hitherto unresolved and perhaps insoluble philosophical problems, above all the mind-body problem, i.e. the relationship and interaction of mind and body, the problem of mental and physical causation, and the processing of “external” and internal stimuli, which constitutes the basis of perception, imagination, memory, belief, knowledge, intention, choice, and action.