Idealism

German Idealism carries idealism to its summit: the ground of the real is not matter but mind. Yet it is no longer the idealism of a Berkeley, for whom things exist only insofar as they are perceived by finite minds: it is an absolute idealism, in which nature and history are the moments of one and the same Spirit that thinks itself and recognizes itself in its other. Schelling posits the identity of nature and mind; Hegel makes substance a subject.

Hegel, Phenomenology of Spirit (Preface) · Schelling, System of Transcendental Idealism

Reality is measured by the stability of being: what stays self-identical is more real than what wavers between being and non-being. Now the sensible, always in becoming, has only a borrowed being, held by participation (the relation by which the sensible derives its being from the intelligible) in the intelligible that grounds it. Hence a hierarchical dualism (the division of the real into two orders, the intelligible and the sensible, soul and body), two worlds but not on a par: the sensible is the shadow, the intelligible the source. The allegory of the cave turns this into an argument about the human condition, prisoner of copies until it has converted its gaze. Against materialism, it is not the body that grounds the soul, but the intelligible that grounds the sensible.

Plato, Republic, 514a-517a, allegory of the cave · Plotinus, Enneads, V

The criterion of the real, for Advaita, is permanence: only what is never contradicted across states and resolves into nothing else is fully real. But every plural thing arises, changes and passes, and the experience of waking dissolves the dream-world as waking dissolves illusion: plurality therefore has only an empirical, dependent reality, māyā (appearance) superimposed by avidyā upon brahman (the absolute, being-consciousness-bliss, sat-cit-ānanda) alone, which remains self-identical. Against the dualism of Sāṅkhya, which posits two irreducible principles, spirit (puruṣa) and nature (prakṛti), Advaita refuses any ultimate duality: there are not two reals but one, of which matter is only the appearing. And against the materialist it objects that the consciousness which attests every thing cannot itself be one material object among others.

Śaṅkara, Commentary on the Brahma-Sūtras (Brahma-Sūtra-Bhāṣya), I · Chāndogya Upaniṣad, VI

Berkeley starts from a simple empiricist remark: whatever I have an idea of, I have it through the senses, hence as a perception. But to posit, behind my perceptions, a matter that would exist without being perceived is to posit the idea of a thing of which, by definition, I can have no idea: a contradiction. He thus turns Locke's empiricism against matter itself: what we call bodies is only an ordered collection of sensible ideas, and for them to exist is to be perceived. What remains is that which perceives, the mind, the one genuine substance. Far from denying the world, he claims to save it from scepticism by removing the veil of an unknowable matter set between us and it.

Principles of Human Knowledge, §§3-7 · Three Dialogues between Hylas and Philonous, I

The true cannot be thought as inert matter that mind would observe from outside: it must be grasped also as subject. The real is the Idea that unfolds, externalizes itself, then returns to itself in knowing itself; its structure is rational, and matter has truth only through the thought that runs through it. Whether the reach of this idealism is cosmic or merely logical still divides readers.

Phenomenology of Spirit, Preface · Science of Logic, Doctrine of the Concept

A single reality exists without a second, brahman, pure consciousness: neither matter nor the plurality of things are autonomous substances. The world of objects is not sheer nothingness, but it holds only an empirical reality (vyāvahārika), superimposed on brahman by ignorance, as one sees a snake where there is only a rope. This idealism is sui generis: it does not make the world the content of a finite mind, in Berkeley's manner, but refers it wholly to the one absolute consciousness of which things are merely the appearance. The question is thus not "mind or matter?" but "is the manifold real?", to which Śaṅkara answers by non-duality.

Commentary on the Brahma Sūtras, I.1.1-4 · Upadeśasāhasrī

The first book of The World as Will and Representation begins from a radicalized Kantian premise: the world exists only as representation, under the a priori forms of space, time, and causality. But where Kant left the thing-in-itself unknowable, Schopenhauer holds that we have a unique access to it: our body, known from without as representation and from within as will. Materialism is refuted as the philosophy 'of the subject that forgets itself in its own reckoning'; his idealism nonetheless remains singular, since the ground of the real is not mind but blind willing.

The World as Will and Representation, Book I, §1

Whatever is composite presupposes something simple, for an aggregate borrows its reality from its elements: there must therefore exist simple substances, without parts, the monads. But matter, endlessly divisible and extended, is never simple: the true atoms of nature cannot be material but must be of a spiritual order, units whose essence is perception and appetition. Extended matter then has only a derived reality, that of a well-founded phenomenon resulting from the aggregation of monads. This immaterialism answers the problem of the unity of the real that Cartesian extension, always divisible, could not ground; it keeps a dualist tint, the order of bodies and that of souls remaining distinct but harmonized.

Monadology, §1-7 (the monads, simple windowless substances) · Letters to De Volder and Des Bosses (well-founded phenomena)

If the mind conformed to objects, we could never know anything of them a priori; reverse the hypothesis, as Copernicus set the observer at the centre, and let objects conform to our cognition. Then space, time and the categories are not features of things but the forms of the subject under which alone an object can appear to us. The consequence is transcendental idealism: we know only phenomena, never the thing in itself. This boundary saves science (its laws hold necessarily for every phenomenon) without collapsing into Berkeley's idealism, since the thing in itself remains; the phenomenon / noumenon dualism thus kept rules out the fully idealist pole.

Critique of Pure Reason, Transcendental Aesthetic · Prolegomena to Any Future Metaphysics, §13

The argument starts from a premise inherited from Heraclitus: the sensible is in perpetual flux, and of what never ceases to become there can be no science. Yet since we do know the equal, the just, the circle, there must exist stable, intelligible objects of which sensible things are only imperfect reflections: this is the higher degree of reality. The allegory of the cave, where prisoners take shadows for the real, dramatizes this reversal. A dualism Plato never dissolves remains, two distinct orders held side by side, whose relation of "participation" stays problematic, as he himself concedes in the Parmenides.

Republic, VII, 514a-518b (allegory of the cave) · Timaeus, 27d-29d

The real unfolds as a hierarchy of degrees of being, from the One down to matter: the more a thing is one and intelligible, the more real it is; the more dispersed in the sensible, the less. The sensible world is therefore not illusory but the lowest degree, a faint image produced by the Soul that orders and animates the cosmos. Matter, at the bottom of the scale, is all but nothing, sheer lack. This priority of mind leans strongly toward idealism, but it is a Platonic gradation, not the idealism of a Berkeley for whom to be is to be perceived: a duality of intelligible and sensible persists, hence a residual weight on dualism.

Enneads, V, 1 and V, 2 · Enneads, IV, 8 (On the Descent of the Soul into Bodies)