Spinoza can be seen as a pure philosopher, always seeking explanation, always refusing to be satisfied with primitive, inexplicable notions. This purity is most evident in his commitment to the principle that each fact has an explanation, that for each thing that exists there is an explanation that suffices for one to see why that thing exists. Although Spinoza does not himself use the term, this principle is known as the Principle of Sufficient Reason (PSR).

Nevertheless, when it is your lot to have to endure something that is (or seems to you) worse than the ordinary lot of mankind, Spinoza's principle of thinking about the whole, or at any rate about larger matters than your own grief, is a useful one. There are even times when it is comforting to reflect that human life, with all that is contains of evil and suffering, is an infinitesimal part of the life of the universe. Such reflections may not suffice to constitute a religion, but in a painful world they are a help towards sanity and an antidote to the paralysis of utter despair. - about Spinoza

Spinoza’s naturalism and rationalism are nowhere more evident and more relevant to contemporary philosophy than in his philosophy of mind. All there is to thought is the having of ideas, representations of certain things. Thus, in laying down requirements on what it is to have an idea or representation of an object, Spinoza is articulating the essence of the mental.

But orthodox religious scholasticism, in alliance with subjective idealist philosophy, has not ceased to flog Spinoza as a ‘dead dog’, treating him as a living and dangerous opponent. Elementary analysis reveals that the main principles of Spinoza’s thought directly contradict the conception of ‘thought’ developed by modern positivism all along the line. The most modern systems of the twentieth century still clash in sharp antagonism in Spinoza; and that obliges us to analyse the theoretical foundation of his conception very carefully, and to bring out the principles in it that, in rather different forms of expression perhaps, remain the most precious principles of any scientific thinking to this day, and as such are very heatedly disputed by our contemporary opponents of dialectical thought.

The purity of Spinoza’s commitment to explanation can best be articulated in terms of his commitments to the Principle of Sufficient Reason (hereafter, the “PSR”) and to his naturalism.

As regards the philosophy of Spinoza, it is very simple, and on the whole easy to comprehend; the difficulty which it presents is due partly to the limitations of the method in which Spinoza presents his thoughts, and partly to his narrow range of ideas, which causes him in an unsatisfactory way to pass over important points of view and cardinal questions. Spinoza's system is that of Descartes made objective in the form of absolute truth. The simple thought of Spinoza's idealism is this: The true is simply and solely the one substance, whose attributes are thought and extension or nature: and only this absolute unity is reality, it alone is God. It is, as with Descartes, the unity of thought and Being, or that which contains the Notion of its existence in itself. The Cartesian substance, as Idea, has certainly Being included in its Notion; but it is only Being as abstract, not as real Being or as extension (supra, p. 241). With Descartes corporeality and the thinking 'I' are altogether independent Beings; this independence of the two extremes is done away with in Spinozism by their becoming moments of the one absolute Being. This expression signifies that Being must be grasped as the unity of opposites; the chief consideration is not to let slip the opposition and set it aside, but to reconcile and resolve it. Since then it is thought and Being, and no longer the abstractions of the finite and infinite, or of limit and the unlimited, that form the opposition (supra, p. 161), Being is here more definitely regarded as extension; for in its abstraction it would be really only that return into itself, that simple equality with itself, which constitutes thought (supra, p. 229). The pure thought of Spinoza is therefore not the simple universal of Plato, for it has likewise come to know the absolute opposition of Notion and Being.

Spinoza redefines the problem of Modern philosophy, which is the conquest of the world and the liberation of humanity, and destroys both its multiple antinomies and the continually resurgent separation (dualistic, transcendental, etc.) in the theory of knowledge and history, in the same way that criticism has always destroyed Zenonian sophism: moving forward, putting reality in motion. Spinoza's philosophy is born from the radicalization of the ontological paradox of being: in the recognition that the hypostasis, the only possible hypostasis, is that of the world and of the development of its necessity from physics to practice. It is a conception of the world that immediately produces, as if from its own basis, a completely modern conception of science and worldly knowledge, both technical and liberatory. It is a radically materialistic conception of being and of the world.

Spinoza is a highly systematic thinker, but still I do not think I can offer a single key for all things Spinozistic. Personally, one thing which got me excited about Spinoza is his philosophical boldness, i.e., his willingness to pursue philosophical exploration as far as he can, making very little concessions to commonly accepted beliefs and norms. In terms of content, I take his attempt to conceive of God, nature, and ethics in a manner that is free from anthropomorphism and anthropocentric illusions as one of the deepest elements of his philosophical thinking. A closely related issue is his advocacy of actual infinity (an issue that has been mostly neglected in recent literature). Finally, the very attempt to do philosophy systematically (rather than rely on fragmented and disassociated intuitions) and transparently (laying bare the logical structure of his arguments) commands my respect, indeed admiration.

What also fascinated me about Spinoza was his philosophical strategy. Jacques Derrida has spoken a lot about strategy in philosophy, and he is perfectly right, since every philosophy is a dispositif of theoretical combat that disposes of theses as so many strongholds or prominent places so as to be able, in its aim and strategic attacks, to take over the theoretical places fortified and occupied by the adversary. Yet Spinoza began with God! [...] A supreme strategy: he began by taking over the chief stronghold of his adversary, or rather he established himself there as if he were his own adversary, therefore not suspected of being the sworn adversary, and redisposed the theoretical fortress in such a way as to turn it completely around, as one turns around cannons against the fortress's own occupant.

Now that I have sketched my main purpose, it is time to ex­plain why a book dedicated to new ideas on the nature and signif­icance of human feeling should invoke Spinoza in the title. Since I am not a philosopher and this book is not about Spinoza's phi­losophy, it is sensible to ask: why Spinoza? The short explanation is that Spinoza is thoroughly relevant to any discussion of human emotion and feeling. Spinoza saw drives, motivations, emotions, and feelings—an ensemble Spinoza called affects—as a central aspect of humanity. Joy and sorrow were two prominent concepts in his attempt to comprehend human beings and suggest ways in which their lives could be lived better.

When Spinoza in the seventeenth century used the word reason, he meant an attitude toward life in which the mind united the emotions with the ethical goals and other aspects of the “whole man.” When people today use the term they almost always imply a splitting of the personality. They ask in one form or another: “Should I follow reason or give way to sensual passions and needs or be faithful to my ethical duty?

Spinoza's views on God, religion and society have lost none of their relevance. At a time when Americans seem willing to bargain away their freedoms for security, when politicians talk of banning people of a certain faith from our shores, and when religious zealotry exercises greater influence on matters of law and public policy, Spinoza's philosophy – especially his defence of democracy, liberty, secularity and toleration – has never been more timely. In his distress over the deteriorating political situation in the Dutch Republic, and despite the personal danger he faced, Spinoza did not hesitate to boldly defend the radical Enlightenment values that he, along with many of his compatriots, held dear. In Spinoza we can find inspiration for resistance to oppressive authority and a role model for intellectual opposition to those who, through the encouragement of irrational beliefs and the maintenance of ignorance, try to get citizens to act contrary to their own best interests.

Spinoza’s metaphysics is, in many ways, an effort to tap into the underlying rationalist motivations of Descartes’s metaphysics and to follow through on these motivations more consistently than Descartes ever did. Employing the Cartesian notions of substance, attribute, and mode, and wielding strongly rationalist principles only hinted at in Descartes—such as the PSR and the Principle of the Identity of Indiscernibles—Spinoza is able to mount a powerful argument for substance monism, for the view that there is, fundamentally, only one thing in the world.

We have thus begun to think of Spinoza's "radicalism" differently than the past century did. Now we see that the bold innovations of Spinoza were only consequences, rather than foundations. The fact that now gains in importance is that — compared to the significance of Descartes, Hobbes, and Leibniz — Spinoza is only of secondary significance in the history of the core sciences, that is, in the history of natural science, on the one hand, and of natural right, on the other. And the fact that Spinoza achieved more general recognition only toward the end of the eighteenth century is now also understandable: he could be accepted only at the moment when the "querelle des anciens et des modemes" within philosophy had been decided on the main point in favor of the moderns, and when what mattered was the restoration, for the purpose of correcting the modern idea, of certain positions of the premodern world that had been knocked over in the first onslaught; for Spinoza — who stood on the foundation of modern philosophy laid by Descartes and Hobbes — had carried along into the modern world, which he already found in existence, the ideal of life of the premodern (ancient-medieval) tradition, the ideal of the (theoretical) knowledge of God.