Idealism in philosophy, also known as philosophical idealism or metaphysical idealism, is the set of metaphysical perspectives asserting that, most fundamentally, reality is equivalent to mind, spirit, or consciousness; that reality is entirely a mental construct; or that ideas are the highest form of reality or have the greatest claim to being considered "real". The radical latter view is often first credited to the Ancient Greek philosopher Plato as part of a theory now known as Platonic idealism. Besides in Western philosophy, idealism also appears in some Indian philosophy, namely in Vedanta, one of the orthodox schools of Hindu philosophy, and in some streams of Buddhism.
Epistemologically, idealism is accompanied by philosophical skepticism about the possibility of knowing the existence of any thing that is independent of the human mind. Ontologically, idealism asserts that the existence of things depends upon the human mind; thus, ontological idealism rejects the perspectives of physicalism and dualism, because neither perspective gives ontological priority to the human mind. In contrast to materialism, idealism asserts the primacy of consciousness as the origin and prerequisite of phenomena.
During the European Enlightenment, certain qualified versions of idealism arose, such as George Berkeley's subjective idealism, which proposed that physical objects exist only to the extent that one perceives them and thus the physical world does not exist outside of a mind. According to Berkeley, who was an Anglican Bishop, a single eternal mind keeps all of physical reality stable, and this is God.
By contrast, Immanuel Kant said that idealism "does not concern the existence of things," but that "our modes of representation" of things such as space and time are not "determinations that belong to things in themselves," but are essential features of the human mind. Thus, Kant's transcendental idealism proposes that objects of experience rely upon their existence in the human mind that perceives the objects, and that the nature of the object-in-itself is external to human experience, unable to be conceived without the application of categories, which give structure to the human experience of reality. Kant's philosophy would be reinterpreted by Arthur Schopenhauer and by German idealists such as J.G. Fichte, F.W.J. Schelling, and G.W.F. Hegel. This tradition, which emphasized the mental or "ideal" character of all phenomena, gave birth to idealistic and subjectivist schools ranging from British idealism to phenomenalism to existentialism.
Indian philosophers proposed the earliest arguments that the world of experience is grounded in the mind's perception of the physical world. Hindu idealism gave panentheistic arguments for the existence of an all-pervading consciousness as the true nature, as the true grounding of reality. In contrast, the Yogācāra school, which arose within Mahayana Buddhism in India in the 4th century AD, based its "mind-only" idealism to a greater extent on phenomenological analyses of personal experience.
Idealism as a philosophy came under heavy attack in the West at the turn of the 20th century. The most influential critics of both epistemological and ontological idealism were G. E. Moore and Bertrand Russell, but its critics also included the new realists. The attacks by Moore and Russell were so influential that even more than 100 years later "any acknowledgment of idealistic tendencies is viewed in the English-speaking world with reservation." However, many aspects and paradigms of idealism did still have a large influence on subsequent philosophy.
Idealism is a term with several related meanings. It comes via Latin idea from the Ancient Greek idea (ἰδέα) from idein (ἰδεῖν), meaning "to see." The term entered the English language by 1743. It was first used in the abstract metaphysical sense "belief that reality is made up only of ideas" by Christian Wolff in 1747. The term re-entered the English language in this abstract sense by 1796.
In ordinary language, as when speaking of Woodrow Wilson's political idealism, it generally suggests the priority of ideals, principles, values, and goals over concrete realities. Idealists are understood to represent the world as it might or should be, unlike pragmatists, who focus on the world as it presently is. In the arts, similarly, idealism affirms imagination and attempts to realize a mental conception of beauty, a standard of perfection, juxtaposed to aesthetic naturalism and realism. The term idealism is also sometimes used in a sociological sense, which emphasizes how human ideas—especially beliefs and values—shape society.
Metaphysical idealism is an ontological doctrine that holds that reality itself is incorporeal or experiential at its core. Beyond this, idealists disagree on which aspects of the mental are more basic. Platonic idealism affirms that abstractions are more basic to reality than the things we perceive, while subjective idealists and phenomenalists tend to privilege sensory experience over abstract reasoning. Epistemological idealism is the view that reality can only be known through ideas, that only psychological experience can be apprehended by the mind.
Subjective idealists like George Berkeley are anti-realists in terms of a mind-independent world. However, not all idealists restrict the real or the knowable to our immediate subjective experience. Objective idealists make claims about a transempirical world, but simply deny that this world is essentially divorced from or ontologically prior to the mental. Thus, Plato affirms an objective and knowable reality transcending our subjective awareness—a rejection of epistemological idealism—but proposes that this reality is grounded in ideal entities, a form of metaphysical idealism. Nor do all metaphysical idealists agree on the nature of the ideal; for instance, according to Plato, the fundamental entities were non-mental abstract forms.
As a rule, transcendental idealists like Kant affirm idealism's epistemic side without committing themselves to whether reality is ultimately mental; objective idealists like Plato affirm reality's metaphysical basis in the mental or abstract without restricting their epistemology to ordinary experience; and subjective idealists like Berkeley affirm both metaphysical and epistemological idealism.
Idealism as a form of metaphysical monism holds that consciousness, not matter, is the ground of all being. It is monist because it holds that there is only one type of thing in the universe and idealist because it holds that one thing to be consciousness.
Anaxagoras (480 BC) taught that "all things" were created by Nous ("Mind"). He held that Mind held the cosmos together and gave human beings a connection to the cosmos or a pathway to the divine.
Plato's theory of forms or "ideas" describes ideal forms (for example the platonic solids in geometry or abstracts like Goodness and Justice), as universals existing independently of any particular instance. Arne Grøn calls this doctrine "the classic example of a metaphysical idealism as a transcendent idealism," while Simone Klein calls Plato "the earliest representative of metaphysical objective idealism." Nevertheless, Plato holds that matter is real, though transitory and imperfect, and is perceived by our body and its senses and given existence by the eternal ideas that are perceived directly by our rational soul. Plato was therefore a metaphysical and epistemological dualist, an outlook that modern idealism has striven to avoid: Plato's thought cannot therefore be counted as idealist in the modern sense.
With the neoplatonist Plotinus, wrote Nathaniel Alfred Boll "there even appears, probably for the first time in Western philosophy, idealism that had long been current in the East even at that time, for it taught... that the soul has made the world by stepping from eternity into time..." Similarly, in regard to passages from the Enneads, "The only space or place of the world is the soul" and "Time must not be assumed to exist outside the soul." Ludwig Noiré wrote: "For the first time in Western philosophy we find idealism proper in Plotinus". However, Plotinus does not address whether we know external objects, unlike Schopenhauer and other modern philosophers.
Christian theologians have held idealist views, often based on neoplatonism, despite the influence of Aristotelian scholasticism from the 12th century onward. However, there is certainly a sense in which the scholastics retained the idealism that came via Augustine right back to Plato.
Later western theistic idealism such as that of Hermann Lotze offers a theory of the "world ground" in which all things find their unity: it has been widely accepted by Protestant theologians. Several modern religious movements, for example the organizations within the New Thought Movement and the Unity Church, may be said to have a particularly idealist orientation. The theology of Christian Science includes a form of idealism: it teaches that all that truly exists is God and God's ideas; that the world as it appears to the senses is a distortion of the underlying spiritual reality, a distortion that may be corrected (both conceptually and in terms of human experience) through a reorientation (spiritualization) of thought.
Wang Yangming, a Ming Chinese neo-Confucian philosopher, official, educationist, calligraphist and general, held that objects do not exist entirely apart from the mind because the mind shapes them. It is not the world that shapes the mind but the mind that gives reason to the world, so the mind alone is the source of all reason, having an inner light, an innate moral goodness and understanding of what is good.
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There are currents of idealism throughout Indian philosophy, ancient and modern. Hindu idealism often takes the form of monism or non-dualism, espousing the view that a unitary consciousness is the essence or meaning of the phenomenal reality and plurality.
Buddhist idealism on the other hand is more epistemic and is not a metaphysical monism, which Buddhists consider eternalistic and hence not the Middle Way between extremes espoused by the Buddha.
The oldest reference to Idealism in Vedic texts is in Purusha Sukta of the Rig Veda. This Sukta espouses panentheism by presenting cosmic being Purusha as both pervading all universe and yet being transcendent to it. Absolute idealism can be seen in Chāndogya Upaniṣad, where things of the objective world like the five elements and the subjective world such as will, hope, memory etc. are seen to be emanations from the Self.
Idealist notions have been propounded by the Vedanta schools of thought, which use the Vedas, especially the Upanishads as their key texts. Idealism was opposed by dualists Samkhya, the atomists Vaisheshika, the logicians Nyaya, the linguists Mimamsa and the materialists Cārvāka. There are various sub schools of Vedanta, like Advaita Vedanta (non-dual), Vishishtadvaita and Bhedabheda Vedanta (difference and non-difference).
The schools of Vedanta all attempt to explain the nature and relationship of Brahman (universal soul or Self) and Atman (individual self), which they see as the central topic of the Vedas. One of the earliest attempts at this was Bādarāyaņa's Brahma Sutras, which is canonical for all Vedanta sub-schools. Advaita Vedanta is a major sub school of Vedanta which holds a non-dual Idealistic metaphysics. According to Advaita thinkers like Adi Shankara (788–820) and his contemporary Maṇḍana Miśra, Brahman, the single unitary consciousness or absolute awareness, appears as the diversity of the world because of maya or illusion, and hence perception of plurality is mithya, error. The world and all beings or souls in it have no separate existence from Brahman, universal consciousness, and the seemingly independent soul (jiva) is identical to Brahman. These doctrines are represented in verses such as brahma satyam jagan mithya; jīvo brahmaiva na aparah (Brahman is alone True, and this world of plurality is an error; the individual self is not different from Brahman). Other forms of Vedanta like the Vishishtadvaita of Ramanuja and the Bhedabheda of Bhāskara are not as radical in their non-dualism, accepting that there is a certain difference between individual souls and Brahman. Dvaita school of Vedanta by Madhvacharya maintains the opposing view that the world is real and eternal. It also argues that real Atman fully depends on the reflection of independent Brahman.
The Tantric tradition of Kashmir Shaivism has also been categorized by scholars as a form of Idealism. The key thinker of this tradition is the Kashmirian Abhinavagupta (975–1025 CE).
Modern Vedic Idealism was defended by the influential Indian philosopher Sarvepalli Radhakrishnan in his 1932 An Idealist View of Life and other works, which espouse Advaita Vedanta. The essence of Hindu Idealism is captured by such modern writers as Sri Nisargadatta Maharaj, Sri Aurobindo, P. R. Sarkar, and Sohail Inayatullah.
Buddhist views which can be said to be similar to Idealism appear in Mahayana Buddhist texts such as the Samdhinirmocana sutra, Laṅkāvatāra Sūtra, Dashabhumika sutra, etc. These were later expanded upon by Indian Buddhist philosophers of the influential Yogacara school, like Vasubandhu, Asaṅga, Dharmakīrti, and Śāntarakṣita. Yogacara thought was also promoted in China by Chinese philosophers and translators like Xuanzang.
There is a modern scholarly disagreement about whether Yogacara Buddhism can be said to be a form of idealism. As Saam Trivedi notes: "on one side of the debate, writers such as Jay Garfield, Jeffrey Hopkins, Paul Williams, and others maintain the idealism label, while on the other side, Stefan Anacker, Dan Lusthaus, Richard King, Thomas Kochumuttom, Alex Wayman, Janice Dean Willis, and others have argued that Yogacara is not idealist." The central point of issue is what Buddhist philosophers like Vasubandhu who used the term vijñapti-matra ("representation-only" or "cognition-only") and formulated arguments to refute external objects actually meant to say.
Vasubandhu's works include a refutation of external objects or externality itself and argues that the true nature of reality is beyond subject-object distinctions. He views ordinary consciousness experience as deluded in its perceptions of an external world separate from itself and instead argues that all there is Vijñapti (representation or conceptualization). Hence Vasubandhu begins his Vimsatika with the verse: All this is consciousness-only, because of the appearance of non-existent objects, just as someone with an optical disorder may see non-existent nets of hair.
Likewise, the Buddhist philosopher Dharmakirti's view of the apparent existence of external objects is summed up by him in the Pramānaṿārttika ('Commentary on Logic and Epistemology'): Cognition experiences itself, and nothing else whatsoever. Even the particular objects of perception, are by nature just consciousness itself.
While some writers like Jay Garfield hold that Vasubandhu is a metaphysical idealist, others see him as closer to an epistemic idealist like Kant who holds that our knowledge of the world is simply knowledge of our own concepts and perceptions of a transcendental world. Sean Butler upholding that Yogacara is a form of idealism, albeit its own unique type, notes the similarity of Kant's categories and Yogacara's Vāsanās, both of which are simply phenomenal tools with which the mind interprets the noumenal realm. Unlike Kant however who holds that the noumenon or thing-in-itself is unknowable to us, Vasubandhu holds that ultimate reality is knowable, but only through non-conceptual yogic perception of a highly trained meditative mind.
Writers like Dan Lusthaus who hold that Yogacara is not a metaphysical idealism point out, for example, that Yogācāra thinkers did not focus on consciousness to assert it as ontologically real, but simply to analyze how our experiences and thus our suffering is created. As Lusthaus notes: "no Indian Yogācāra text ever claims that the world is created by mind. What they do claim is that we mistake our projected interpretations of the world for the world itself, i.e. we take our own mental constructions to be the world." Lusthaus notes that there are similarities to Western epistemic idealists like Kant and Husserl, enough so that Yogacara can be seen as a form of epistemological idealism. However he also notes key differences like the concepts of karma and nirvana. Saam Trivedi meanwhile notes the similarities between epistemic idealism and Yogacara, but adds that Yogacara Buddhism is in a sense its own theory.
Similarly, Thomas Kochumuttom sees Yogacara as "an explanation of experience, rather than a system of ontology" and Stefan Anacker sees Vasubandhu's philosophy as a form of psychology and as a mainly therapeutic enterprise.
Main article: Subjective idealism
Subjective idealism (also known as immaterialism) describes a relationship between experience and the world in which objects are no more than collections or bundles of sense data in the perceiver. Proponents include Berkeley, Bishop of Cloyne, an Anglo-Irish philosopher who advanced a theory he called "immaterialism," later referred to as "subjective idealism," contending that individuals can only know sensations and ideas of objects directly, not abstractions such as "matter," and that ideas also depend upon being perceived for their very existence - esse est percipi; "to be is to be perceived."
Arthur Collier published similar assertions though there seems to have been no influence between the two contemporary writers. The only knowable reality is the represented image of an external object. Matter as a cause of that image, is unthinkable and therefore nothing to us. An external world as absolute matter unrelated to an observer does not exist as far as we are concerned. The universe cannot exist as it appears if there is no perceiving mind. Collier was influenced by An Essay Towards the Theory of the Ideal or Intelligible World by Cambridge Platonist John Norris (1701).
Paul Brunton, a British philosopher, mystic, traveler, and guru, taught a type of idealism called "mentalism," similar to that of Bishop Berkeley, proposing a master world-image, projected or manifested by a world-mind, and an infinite number of individual minds participating. A tree does not cease to exist if nobody sees it because the world-mind is projecting the idea of the tree to all minds.
Epistemological idealism is a subjectivist position in epistemology that holds that what one knows about an object exists only in one's mind. Proponents include Brand Blanshard.
A. A. Luce and John Foster are other subjectivists. Luce, in Sense without Matter (1954), attempts to bring Berkeley up to date by modernizing his vocabulary and putting the issues he faced in modern terms, and treats the Biblical account of matter and the psychology of perception and nature. Foster's The Case for Idealism argues that the physical world is the logical creation of natural, non-logical constraints on human sense-experience. Foster's latest defense of his views (phenomenalistic idealism) is in his book A World for Us: The Case for Phenomenalistic Idealism.
Critics of subjective idealism include Bertrand Russell's popular 1912 book The Problems of Philosophy, Australian philosopher David Stove, Alan Musgrave, and John Searle.
Main article: Transcendental idealism
Transcendental idealism is a doctrine founded by Immanuel Kant in the eighteenth century. It maintains that we cannot known more of reality that its appearance to us, that is, according to our capacities of sensibility and understanding.
His Critique of Pure Reason (2nd ed.) contains a section entitled "Refutation of Idealism", which distinguishes transcendental idealism from Descartes's sceptical idealism and Berkeley's anti-realist strain of subjective idealism. The section "Paralogisms of Pure Reason" is also an implicit critique of Descartes's idealism. Kant says that it is not possible to infer the "I" as an object (Descartes' cogito ergo sum) purely from "the spontaneity of thought." Kant focused on ideas drawn from British philosophers such as Locke, Berkeley and Hume, but distinguished his transcendental or critical idealism from previous varieties:
The thesis of all genuine idealists, from the Eleatic School up to Bishop Berkeley, is contained in this formula: "All cognition through the senses and experience is nothing but sheer illusion, and there is truth only in the ideas of pure understanding and reason."
The principle that governs and determines my idealism throughout is, on the contrary: "All cognition of things out of mere pure understanding or pure reason is nothing but sheer illusion, and there is truth only in experience."
According to the version of transcendental idealism propounded by Arthur Schopenhauer, mental pictures are what constitute subjective knowledge. The ideal, for him, is what can be attributed to our own minds; the images in our head are what comprise the ideal. This is to say that we are restricted to our own consciousness. The world that appears is only a representation, which is all that we directly and immediately know. All objects that are external to the mind are known indirectly. In his own words, "the objective, as such, always and essentially has its existence in the consciousness of a subject; it is therefore the subject's representation, and consequently is conditioned by the subject, and moreover by the subject's forms of representation, which belong to the subject and not to the object."
Charles Bernard Renouvier was the first philosopher in France to formulate a complete idealistic system since Nicolas Malebranche. His system is based on Immanuel Kant's, as his chosen term "néo-criticisme" indicates. It is a transformation rather than a continuation of Kantianism.
Main article: Objective idealism
Objective idealism asserts that the reality of experiencing combines and transcends the realities of the object experienced and of the mind of the observer. Proponents include Thomas Hill Green, Josiah Royce, Benedetto Croce, and Charles Sanders Peirce.
Main article: Absolute idealism
F. W. J. Schelling (1775–1854) claimed that J. G. Fichte's "I" needs the Not-I, because there is no subject without object, and vice versa. So there is no difference between the subjective and the objective, that is, the ideal and the real. This is Schelling's "absolute identity": the ideas or mental images in the mind are identical to the extended objects which are external to the mind.
Absolute idealism is G. W. F. Hegel's account of how existence is comprehensible as an all-inclusive whole. Hegel called his philosophy "absolute" idealism in contrast to the "subjective idealism" of Berkeley and the "transcendental idealism" of Kant and Fichte. The exercise of reason and intellect enables the philosopher to know ultimate historical reality, the phenomenological constitution of self-determination, the dialectical development of self-awareness in the realm of history.
In his Science of Logic (1812–1814) Hegel argues that finite qualities are not fully "real" because they depend on other finite qualities to determine them. Qualitative infinity, on the other hand, would be more self-determining and hence more fully real. Similarly finite natural things are less "real"—because they are less self-determining—than spiritual things like morally responsible people, ethical communities and God. So any doctrine, such as materialism, that asserts that finite qualities or natural objects are fully real is mistaken.
Hegel certainly intends to preserve what he takes to be true of German Idealism, in particular Kant's insistence that ethical reason can and does go beyond finite inclinations. For Hegel there must be some identity of thought and being for the "subject" (any human observer) to be able to know any observed "object" (any external entity, possibly even another human) at all. Under Hegel's concept of "subject-object identity," subject and object both have spirit (Hegel's ersatz, redefined, nonsupernatural "God") as their inner reality—and in that sense are identical. But until spirit's "self-realization" occurs, the subject (a human mind) mistakenly thinks every "object" it observes is something "alien," meaning something separate or apart from "subject." In Hegel's words, "The object is revealed to it [to "subject"] by [as] something alien, and it does not recognize itself." Self-realization occurs when the speculative philosopher (e.g., Hegel) arrives on the scene and realizes that every "object" is himself, because both subject and object are essentially spirit. When self-actualization is achieved and spirit knows itself absolutely, the "finite" human recognized itself as the "infinite" ("God," divine), replacing the supernatural God of "picture-thought" or "representation" [Vorstellung] characteristic of positive religion.
Actual idealism is a form of idealism developed by Giovanni Gentile that grew into a "grounded" idealism contrasting Kant and Hegel. The idea is a version of Occam's razor; the simpler explanations are always correct. Actual idealism is the idea that reality is the ongoing act of thinking, or in Italian "pensiero pensante". Any action done by humans is classified as human thought because the action was done due to predisposed thought. He further believes that thoughts are the only concept that truly exist since reality is defined through the act of thinking. This idea was derived from Gentile's paper, "The Theory of Mind As Pure Act."
Since thoughts are actions, any conjectured idea can be enacted. This idea not only affects the individual's life, but everyone around them, which in turn affects the state since the people are the state. Therefore, thoughts of each person are subsumed within the state. The state is a composition of many minds that come together to change the country for better or worse.
Gentile theorizes that thoughts can only be conjectured within the bounds of known reality; abstract thinking does not exist. Thoughts cannot be formed outside our known reality because we are the reality that halt ourselves from thinking externally. With accordance to "The Act of Thought of Pure Thought," our actions comprise our thoughts, our thoughts create perception, perceptions define reality, thus we think within our created reality.
The present act of thought is reality but the past is not reality; it is history. The reason being, past can be rewritten through present knowledge and perspective of the event. The reality that is currently constructed can be completely changed through language (e.g. bias (omission, source, tone)). The unreliability of the recorded reality can skew the original concept and make the past remark unreliable. Actual idealism is regarded as a liberal and tolerant doctrine since it acknowledges that every being picturizes reality, in which their ideas remained hatched, differently. Even though, reality is a figment of thought.
Even though core concept of the theory is famous for its simplification, its application is regarded as extremely ambiguous. Over the years, philosophers have interpreted it numerously different ways: Holmes took it as metaphysics of the thinking act; Betti as a form of hermeneutics; Harris as a metaphysics of democracy; Fogu as a modernist philosophy of history.
Giovanni Gentile was a key supporter of fascism, regarded by many as the "philosopher of fascism." Gentile's philosophy was the key to understating fascism as it was believed by many who supported and loved it. They believed, if priori synthesis of subject and object is true, there is no difference between the individuals in society; they're all one. Which means that they have equal right, roles, and jobs. In fascist state, submission is given to one leader because individuals act as one body. In Gentile's view, far more can be accomplished when individuals are under a corporate body than a collection of autonomous individuals.
Pluralistic idealism takes the view that there are many individual minds that together underlie the existence of the observed world and make possible the existence of the physical universe. Pluralistic idealism does not assume the existence of a single ultimate mental reality.
Personalism is the view that the minds that underlie reality are the minds of persons. Borden Parker Bowne, a philosopher at Boston University, a founder and popularizer of personal idealism, presented it as a substantive reality of persons, the only reality, as known directly in self-consciousness. Reality is a society of interacting persons dependent on the Supreme Person of God. Other proponents include George Holmes Howison and J. M. E. McTaggart.
Howison's personal idealism  was also called "California Personalism" by others to distinguish it from the "Boston Personalism" which was of Bowne. Howison maintained that both impersonal, monistic idealism and materialism run contrary to the experience of moral freedom. To deny freedom to pursue truth, beauty, and "benignant love" is to undermine every profound human venture, including science, morality, and philosophy. Personalistic idealists Borden Parker Bowne and Edgar S. Brightman and realistic (in some senses of the term, though he remained influenced by neoplatonism) personal theist Saint Thomas Aquinas address a core issue, namely that of dependence upon an infinite personal God.
Howison, in his book The Limits of Evolution and Other Essays Illustrating the Metaphysical Theory of Personal Idealism, created a democratic notion of personal idealism that extended all the way to God, who was no more the ultimate monarch but the ultimate democrat in eternal relation to other eternal persons. J. M. E. McTaggart's idealist atheism and Thomas Davidson's apeirotheism resemble Howisons personal idealism.
J. M. E. McTaggart argued that minds alone exist and only relate to each other through love. Space, time and material objects are unreal. In The Unreality of Time he argued that time is an illusion because it is impossible to produce a coherent account of a sequence of events. The Nature of Existence (1927) contained his arguments that space, time, and matter cannot possibly be real. In his Studies in Hegelian Cosmology, he declared that metaphysics are not relevant to social and political action. McTaggart "thought that Hegel was wrong in supposing that metaphysics could show that the state is more than a means to the good of the individuals who compose it". For McTaggart "philosophy can give us very little, if any, guidance in action... Why should a Hegelian citizen be surprised that his belief as to the organic nature of the Absolute does not help him in deciding how to vote? Would a Hegelian engineer be reasonable in expecting that his belief that all matter is spirit should help him in planning a bridge?"
Thomas Davidson taught a philosophy called "apeirotheism", a "form of pluralistic idealism...coupled with a stern ethical rigorism" which he defined as "a theory of Gods infinite in number." The theory was indebted to Aristotle's pluralism and his concepts of Soul, the rational, living aspect of a living substance which cannot exist apart from the body because it is not a substance but an essence, and nous, rational thought, reflection and understanding. Although a perennial source of controversy, Aristotle arguably views the latter as both eternal and immaterial in nature, as exemplified in his theology of unmoved movers. Identifying Aristotle's God with rational thought, Davidson argued, contrary to Aristotle, that just as the soul cannot exist apart from the body, God cannot exist apart from the world.
The English psychologist and philosopher James Ward inspired by Leibniz and panpsychism had also defended a form of pluralistic idealism. According to Ward the universe is composed of "psychic monads" of different levels, interacting for mutual self-betterment.
Idealist notions took a strong hold among physicists of the early 20th century confronted with the paradoxes of quantum physics and the theory of relativity. In The Grammar of Science, Preface to the 2nd Edition, 1900, Karl Pearson wrote, "There are many signs that a sound idealism is surely replacing, as a basis for natural philosophy, the crude materialism of the older physicists." This book influenced Einstein's regard for the importance of the observer in scientific measurements. In § 5 of that book, Pearson asserted that "...science is in reality a classification and analysis of the contents of the mind..." Also, "...the field of science is much more consciousness than an external world."
Arthur Eddington, a British astrophysicist of the early 20th century, wrote in his book The Nature of the Physical World that the stuff of the world is mind-stuff, adding that "The mind-stuff of the world is, of course, something more general than our individual conscious minds." Ian Barbour, in his book Issues in Science and Religion, cites Arthur Eddington's The Nature of the Physical World (1928) as a text that argues The Heisenberg Uncertainty Principles provides a scientific basis for "the defense of the idea of human freedom" and his Science and the Unseen World (1929) for support of philosophical idealism "the thesis that reality is basically mental."
The physicist Sir James Jeans wrote: "The stream of knowledge is heading towards a non-mechanical reality; the Universe begins to look more like a great thought than like a great machine. Mind no longer appears to be an accidental intruder into the realm of matter... we ought rather hail it as the creator and governor of the realm of matter." Jeans, in an interview published in The Observer (London), when asked the question: "Do you believe that life on this planet is the result of some sort of accident, or do you believe that it is a part of some great scheme?" replied, "I incline to the idealistic theory that consciousness is fundamental... In general the universe seems to me to be nearer to a great thought than to a great machine."
The chemist Ernest Lester Smith, a member of the occult movement theosophy, wrote a book Intelligence Came First (1975) in which he claimed that consciousness is a fact of nature and that the cosmos is grounded in and pervaded by mind and intelligence.
Bernard d'Espagnat, a French theoretical physicist best known for his work on the nature of reality, wrote a paper titled The Quantum Theory and Reality. According to the paper, "The doctrine that the world is made up of objects whose existence is independent of human consciousness turns out to be in conflict with quantum mechanics and with facts established by experiment.". In a Guardian article entitled "Quantum Weirdness: What We Call 'Reality' is Just a State of Mind", d'Espagnat wrote, "the basic components of objects – the particles, electrons, quarks etc. – cannot be thought of as 'self-existent'." He further writes that his research in quantum physics has led him to conclude that an "ultimate reality" exists, which is not embedded in space or time.
Desperately difficult texts inevitably elicit desperate hermeneutical measures. Aristotle's De Anima, book three, chapter five, is evidently one such text. At least since the time of Alexander of Aphrodisias, scholars have felt compelled to draw some remarkable conclusions regarding Aristotle's brief remarks in this passage regarding intellect. One such claim is that in chapter five, Aristotle introduces a second intellect, the so-called 'agent intellect', an intellect distinct from the 'passive intellect', the supposed focus of discussion up until this passage. This view is a direct descendant of the view of Alexander himself, who identified the agent intellect with the divine intellect. Even the staunchest defender of such a view is typically at a loss to give a plausible explanation of why the divine intellect pops into and then out of the picture in the intense and closely argued discussion of the human intellect that goes from chapter four through to the end of chapter seven.