Main features:
(i) Matter is nothing but a cluster of qualities; both primary qualities (extension, motion) and secondary qualities (colour, taste) are ideas in the mind.
(ii) Knowledge originates in experience, and experience yields only ideas; therefore, the assumption of an external mind-independent matter is dogmatic and superfluous.
(iii) Sensations are not produced by finite minds themselves; they are imprinted by God, the Infinite Mind, on finite minds according to fixed laws of nature.
(iv) Only minds — finite minds and God — exist. The world consists of orderly perceptions caused by God.

Critical estimate:
(a) Neo-Realists like G. E. Moore and Bertrand Russell argue that objects exist independently of being perceived; perception reveals but does not constitute its object.
(b) The argument from inseparability of percept and percipient does not prove their identity.
(c) The variety of our sensations seems to require an independent variety of real objects.
(d) The theory tends towards solipsism, denying the public, shared world of common experience.
Despite these objections, Berkeley’s theory marks a powerful protest against materialism and emphasises the indispensable role of consciousness in knowledge.

Main doctrines of Hegel:
(i) The ultimate reality is the Absolute Spirit or Absolute Idea — pure, self-conscious Thought.
(ii) The Absolute is not static but dynamic; it unfolds itself through the dialectical movement of Thesis, Antithesis and Synthesis.
(iii) Nature is the Absolute in its self-alienated form (unconscious Reason); finite minds are the Absolute coming to self-consciousness.
(iv) “What is rational is actual and what is actual is rational” — reality and reason are identical.
(v) The world is real as the necessary self-expression of the Absolute, thereby reconciling idealism with realism.

Critical estimate:
(a) Modern Realists accept the rationality of nature but deny that nature depends on any cosmic consciousness.
(b) Hegel underestimates the value and creative freedom of the individual; persons become moments of the impersonal Absolute.
(c) Kierkegaard rejected Hegel’s identification of the rational with the actual, insisting on the irreducible reality of individual existence and freedom.
(d) The dialectical scheme is sometimes accused of forcing reality into a rigid logical mould.
Even so, Hegel’s Objective Idealism remains a profound attempt to explain the unity, rationality and purposiveness of the universe.

(i) Subjective Idealism — Berkeley’s view that “to be is to be perceived.” Only minds and their ideas exist.

(ii) Objective Idealism — represented by Plato and Hegel. Reality is constituted by objective Ideas or by an Absolute Spirit, independent of finite minds.

(iii) Absolute Idealism — developed by Hegel, F. H. Bradley and T. H. Green. The whole of reality forms a single, all-inclusive, self-conscious Absolute. Bradley speaks of it as a harmonious experience in which all contradictions are resolved.

(iv) Personalistic Idealism — propounded by B. P. Bowne and E. S. Brightman. Reality consists of a society of persons and a Supreme Person (God). Personality is the highest category of reality.

(v) Phenomenalistic / Transcendental Idealism — Kant’s doctrine that the human mind imposes the forms of space, time and the categories of understanding on raw sense-data, so that we know only phenomena, not things-in-themselves (noumena).

(vi) Indian Idealism — found in Advaita Vedanta of Shankara (Brahman alone is real, the world is maya), Yogachara Buddhism or Vijnanavada (only consciousness is real), and Vishishtadvaita of Ramanuja (Brahman with real internal distinctions).

These forms differ in detail but agree in maintaining that mind, consciousness or spirit is the fundamental nature of reality.

Subjective character:
(i) Berkeley reduces all qualities of matter to ideas in finite minds. The principle “Esse est percipi” makes existence depend on perception.
(ii) Without a perceiving mind, no object can exist; the world is psychological and personal.
(iii) Each finite mind seems to know only its own ideas, raising the danger of solipsism.

Quasi-objective element:
(iv) To save the continuous existence and order of the world, Berkeley argues that God, the Infinite Mind, continually perceives all things and produces sensations in finite minds according to fixed laws.
(v) In this respect, the world has a kind of objectivity in the Divine Mind, somewhat resembling Plato’s eternal Forms.

Conclusion: Despite the appeal to God, Berkeley’s idealism remains essentially subjective, because reality is still constituted by minds and their ideas, not by an independent rational Absolute as in Hegel. It is therefore most accurately classified as Subjective Idealism with a theistic foundation.

(i) Thesis — an initial position, idea or stage of reality is affirmed (e.g., Being).

(ii) Antithesis — the inner contradictions of the thesis emerge, generating its opposite (e.g., Nothing).

(iii) Synthesis — the contradiction between thesis and antithesis is overcome in a higher unity that preserves the truth of both (e.g., Becoming).

Each synthesis becomes the thesis of a new stage, generating its own antithesis, and so on, until the whole of reality is unfolded as the self-realisation of the Absolute Spirit. The dialectical movement thus runs through Logic (the Idea-in-itself), Nature (the Idea outside itself) and Spirit (the Idea returning to itself in self-consciousness). The dialectic is at once a logical method, a metaphysical truth, and a philosophy of history.

Arguments against Idealism:
(i) Common sense: Objects appear to exist whether or not anyone perceives them; the public world is independent of any one mind.
(ii) Scientific objection: Modern science describes a physical universe with laws operating long before human consciousness existed.
(iii) Solipsism: Strict Subjective Idealism risks reducing reality to one’s own mind, which is contrary to experience.
(iv) Inadequate account of error: If reality is mental, the distinction between true and false ideas becomes difficult to draw.

A balanced view, therefore, recognises the strength of idealism in stressing the indispensability of consciousness, while admitting the genuine independence of the natural world emphasised by realism.

Different Forms:
(1) Subjective Idealism — Bishop George Berkeley is its chief exponent. His principle “Esse est percipi” (to be is to be perceived) holds that all reality consists of ideas in finite minds, and ultimately in the Infinite Mind of God.

(2) Objective Idealism — Plato in ancient times and Hegel in the modern period are its great representatives. Plato’s Forms are objective, eternal archetypes; Hegel’s Absolute Spirit is the rational, self-developing ground of all reality.

(3) Absolute Idealism — Hegel, F. H. Bradley and T. H. Green developed this form. Bradley argues that the whole of reality is a single, all-inclusive harmonious experience in which all contradictions are reconciled. Green maintained that nature is the work of an Eternal Self-Consciousness.

(4) Personalistic Idealism — founded by B. P. Bowne and developed by E. S. Brightman. Reality is a society of personal selves and a Supreme Person (God). Personality is the ultimate category of reality.

(5) Phenomenalistic / Transcendental Idealism — Immanuel Kant’s doctrine. The mind imposes its forms of space and time and its categories on raw sense-data; therefore, we know only phenomena, not noumena (things-in-themselves).

(6) Indian Idealism —
(a) Advaita Vedanta of Shankara: Brahman alone is real; the world is maya.
(b) Yogachara / Vijnanavada Buddhism of Asanga and Vasubandhu: only consciousness is real.
(c) Vishishtadvaita of Ramanuja: Brahman with real internal differentiations of souls and matter.

These varied forms reveal that Idealism is not a single fixed doctrine but a broad family of theories united by the central conviction that mind is the foundation of reality.

Critical Estimate of Subjective Idealism:
(i) It rightly insists that knowledge involves consciousness.
(ii) It rightly attacks the dogma of unknown matter.
(iii) But it confuses the act of perception with its object; perception reveals the object, it does not constitute it.
(iv) It cannot adequately account for the regularity, publicity and independence of the natural world.
(v) It tends towards solipsism.

Objective Idealism (Hegel): Holds that reality is the Absolute Spirit or Idea, which unfolds itself dialectically through nature and finite minds. The world is real as the self-expression of the Absolute. Reason and reality are identical: “What is rational is actual and what is actual is rational.”

Critical Estimate of Objective Idealism:
(i) It rightly emphasises the rationality, unity and purposiveness of the universe.
(ii) It successfully reconciles idealism with realism by recognising the world’s reality.
(iii) However, modern Realists deny that nature depends on any consciousness.
(iv) It tends to swallow up individual personality in the impersonal Absolute.
(v) Kierkegaard objected that the dialectical scheme cannot capture concrete individual existence.

Comparison:
(a) Subjective Idealism reduces all reality to finite minds and their ideas; Objective Idealism admits a real, ideal world independent of finite minds.
(b) For Subjective Idealism, existence is “being perceived”; for Objective Idealism, existence is “being thought” by the Absolute.
(c) Subjective Idealism inclines to solipsism; Objective Idealism is universalistic.
(d) Both agree that reality is fundamentally mental or spiritual; they differ on whether mind is finite-personal or universal-impersonal.

Arguments against Idealism:
(i) Common sense: Ordinary experience strongly testifies to the existence of an independent material world.
(ii) Scientific objection: Modern science presupposes a material universe whose laws hold long before and apart from human consciousness.
(iii) Solipsistic danger: Strict Subjective Idealism logically leads to solipsism, which contradicts our shared social experience.
(iv) Inadequate account of error and illusion: If everything is mental, the distinction between true and false ideas is hard to ground.
(v) Realist objection: Perception reveals objects, but does not create them; the act of knowing is not the same as the existence of the thing known.

Tenability of Idealism: Despite criticisms, Idealism remains a powerful philosophical tradition. It rightly stresses (a) the indispensable role of consciousness in knowledge, (b) the rationality and intelligibility of the universe, and (c) the centrality of values. A balanced view, often called critical realism or idealistic realism, accepts the relative independence of the world while insisting that reality is, at its deepest level, spiritual. In this qualified form, idealism continues to be a tenable and significant theory.

(1) Advaita Vedanta of Shankara:
(i) Brahman, pure non-dual consciousness, is the only ultimate reality.
(ii) The world is maya — a beginning-less cosmic illusion superimposed on Brahman, neither real nor unreal.
(iii) The individual self (Atman) is identical with Brahman; this identity is expressed in the great saying “Tat tvam asi” (“That thou art”).
(iv) Knowledge of this identity (jnana) liberates the soul from the cycle of birth and death (moksha).
(v) It is the most rigorous form of monistic Objective Idealism in Indian thought.

(2) Yogachara / Vijnanavada Buddhism (Asanga, Vasubandhu):
(i) Only consciousness (vijnana) is real; external objects are projections of consciousness.
(ii) The storehouse-consciousness (alaya-vijnana) carries the latent impressions (vasanas) which manifest as the experienced world.
(iii) Liberation consists in the purification of consciousness and the cessation of mental projections.
(iv) It is the Indian counterpart of Subjective Idealism, comparable to Berkeley’s view.

(3) Vishishtadvaita of Ramanuja:
(i) Brahman, identified with Ishvara (a personal God), is the sole reality, but with real internal distinctions.
(ii) Souls (cit) and matter (acit) are real attributes of Brahman, related to it as body to soul.
(iii) The world is not maya but the real body of God.
(iv) Liberation is loving devotion (bhakti) and eternal communion with the Supreme Person.
(v) It corresponds to Personalistic Idealism in Western thought.

Common features: All three schools agree that consciousness is fundamental, that liberation is the supreme goal of life, and that reality is ultimately spiritual. They differ in their treatment of the world’s status and the nature of the relation between Brahman and individual souls. Together they constitute the rich heritage of Indian Idealism.