Schopenhauer identifies the thing-in-itself — the inner essence of everything — as will: a blind, unconscious, aimless striving devoid of knowledge, outside of space and time, and free of all multiplicity.

The World as Will and Representation marked the pinnacle of Schopenhauer's philosophical thought; he spent the rest of his life refining, clarifying and deepening the ideas presented in this work without any fundamental changes.

[9][10] There is some debate over the best way to convey, in English, the meaning of Vorstellung, a key concept in Schopenhauer's philosophy that is used in the title of his main work.

"[9] In the introduction to his translation with David Carus (first published 2008), Richard Aquila argues that the reader will not grasp the details of the philosophy of Schopenhauer properly without rendering Vorstellung as "presentation".

Schopenhauer demands that his doctoral dissertation On the Fourfold Root of the Principle of Sufficient Reason, which appeared in 1813, be read before WWR as an introduction.

Referring to On the Fourfold Root, Schopenhauer states in the preface to the first edition of WWR that it is "absolutely impossible to truly understand the present work unless the reader is familiar with this introduction and propaedeutic, and the contents of that essay are presupposed here as much as if they had been included in the book".

However, The World as Will and Representation contains an appendix entitled "Critique of the Kantian philosophy", in which Schopenhauer rejects most of Kant's ethics and significant parts of his epistemology and aesthetics.

Schopenhauer claims that eleven of Kant's categories are superfluous "blind windows" meant for the purposes of architectonic symmetry.

Schopenhauer argues that there are three a priori forms by which our minds render our experience of the world intelligible to ourselves: time, space, and causality.

Much later in his life, in 1844, Schopenhauer published a second edition in two volumes, the first a virtual reprint of the original, and the second a new work consisting of clarifications to and additional reflections on the first.

Presentation and comprehension are both made easier by the separation of four principal perspectives into four Books, connecting what is related and homogeneous with the utmost of care.

[16]His belated fame after 1851 stimulated renewed interest in his seminal work, and led to a third and final edition with 136 more pages in 1859, one year before his death.

Buddhism identifies the individual's pervasive sense of dissatisfaction as driving craving, roughly similar to what Schopenhauer would call the will to life.

The epigraph to volume one is a quotation from Johann Wolfgang von Goethe: Ob nicht Natur zuletzt sich doch ergründe?

The opening sentence of Schopenhauer's work is Die Welt ist meine Vorstellung: "the world is my representation" (alternatively, "idea" or "presentation").

Schopenhauer begins WWR by examining the world as it shows itself to us in our minds: objects ordered necessarily by space and time and by cause-and-effect relationships.

Kant believed that space and time were merely the forms of our intuition by which we must perceive the world of phenomena, and these factors were absent from the thing-in-itself.

The individual is then able to lose himself in the object of aesthetic contemplation and, for a brief moment, escape the cycle of unfulfilled desire as a "pure, will-less subject of knowledge" (reinen, willenlosen Subjekts der Erkenntniß).

This entails the abandonment of the method of cognition bound to the principle of sufficient reason (the only mode appropriate to the service of the will and science).

Compassion arises from a transcendence of this egoism (the penetration of the illusory perception of individuality, so that one can empathise with the suffering of another) and can serve as a clue to the possibility of going beyond desire and the will.

Schopenhauer's praise for asceticism led him to think highly of Buddhism and Vedanta Hinduism, as well as some monastic orders and ascetic practices found in Catholicism.

According to Schopenhauer, the deep truth of the matter is that in cases of the over-affirmation of the will—that is, cases where one individual exerts his will not only for its own fulfillment but for the improper domination of others—he is unaware that he is really identical with the person he is harming, so that the Will in fact constantly harms itself, and justice is done in the moment in which the crime is committed, since the same metaphysical individual is both the perpetrator and the victim.

"[20] Schopenhauer concludes the Fourth Book with the following statement: "...to those in whom the will has turned and denied itself, this very real world of ours, with all its Suns and Milky Ways, is—nothing.

Schopenhauer's Kritik der Kantischen Philosophie opens with the following quote from Voltaire from The Age of Louis XIV: "C'est le privilège du vrai génie, et surtout du génie qui ouvre une carrière, de faire impunément de grandes fautes ('It is the privilege of true genius, and above all the genius who opens a new path, to make great errors with impunity.')

[23] Goethe told his daughter-in-law that he had now pleasure for an entire year, because he would read it completely, contrary to his custom of sampling pages to his liking.

In the years where the work was largely ignored, Jean Paul praised it as "a work of philosophical genius, bold, universal, full of penetration and profoundness—but of a depth often hopeless and bottomless, akin to that melancholy lake in Norway, in whose deep water, beneath the steep rock-walls, one never sees the sun, but only stars reflected",[24] on which Schopenhauer commented: "In my opinion the praise of one man of genius fully makes good the neglect of a thoughtless multitude".

To be mentioned are Wagner (Influence of Schopenhauer on Tristan und Isolde), Schoenberg,[27] Mahler,[28] who cites The World as Will and Representation as "the most profound writing on music he had ever encountered",[29] Thomas Mann, Hermann Hesse, Jorge Luis Borges, Tolstoy, D. H. Lawrence and Samuel Beckett.

Nietzsche commented, "I belong to those readers of Schopenhauer who know perfectly well, after they have turned the first page, that they will read all the others, and listen to every word that he has spoken".

[30] Some read ideas in it that can be found in the theory of evolution, for example, that sexual instinct is a tool of nature to ensure the quality of the offspring.

Schopenhauer argued in favor of transformism by pointing to one of the most important and familiar evidences of the truth of the theory of descent, the homologies in the inner structure of all the vertebrates.