It is only in the
modern era that idealism became a central topic of argumentation among Western philosophers. This was also when the term "idealism" coined by
Christian Wolff (1679–1754), though previous thinkers like Berkeley had argued for it under different names. Idealistic tendencies can be found in the work of some
rationalist philosophers, like
Leibniz and
Nicolas Malebranche (though they did not use the term). Malebranche argued that Platonic ideas (which exist only in the mind of God) are the ultimate ground of our experiences and of the physical world, a view that prefigures later idealist positions. Some scholars also see Leibniz' philosophy as approaching idealism. Guyer et al. write that "his view that the states of
monads can be only perceptions and appetitions (desires) suggests a metaphysical argument for idealism, while his famous thesis that each monad represents the entire universe from its own point of view might be taken to be an epistemological ground for idealism, even if he does not say as much."
Subjective idealism One famous proponent of modern idealism was
Bishop George Berkeley (1685–1753), an Anglo-Irish philosopher who defended a theory he called immaterialism. This kind of idealism is sometimes also called
subjective idealism (also known as
phenomenalistic idealism). Berkeley held that objects exist only to the extent that a mind perceives them and thus the physical world does not exist outside of mind. Berkeley's epistemic argument for this view (found in his
A Treatise Concerning the Principles of Human Knowledge) rests on the
premise that we can only know ideas in the mind. Thus, knowledge does not extend to mind-independent things (
Treatise, 1710: Part I, §2). From this, Berkeley holds that "the existence of an idea consists in being perceived", thus, regarding ideas "their
esse is
percipi", that is, to be is to be perceived (1710: Part I, §3). Berkeley also argued for idealism based on a second key premise: "an idea can be like nothing but an idea" and as such there cannot be any things without or outside mind. This is because for something to be like something else, there must be something they have in common. If something is mind independent, then it must be completely different from ideas. Thus, there can be no relation between ideas in the mind and things "without the mind", since they are not alike. As Berkeley writes, "...I ask whether those supposed originals or external things, of which our ideas are the pictures or representations, be themselves perceivable or no? if they are, then they are ideas, and we have gained our point; but if you say they are not, I appeal to any one whether it be sense, to assert a colour is like something which is invisible; hard or soft, like something which is intangible; and so of the rest." (1710: Part I, §8).
Paul Brunton, a British philosopher and mystic, also taught a similar type of idealism called "mentalism".
A. A. Luce and
John Foster are other subjective idealists. 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.
Epistemic idealism Kant's Transcendental idealism Transcendental idealism was developed by
Immanuel Kant (1724–1804), who was the first philosopher to label himself an "idealist". In his
Critique of Pure Reason, Kant was clear to distinguish his view (which he also called "critical" and "empirical realism") from Berkeley's idealism and from Descartes's views. Kant's philosophy holds that we only have knowledge of our experiences, which consists jointly of intuitions and concepts. As such, our experiences reflect our cognitive structures, not the intrinsic nature of mind-independent things. This means even time and space are not properties of
things in themselves (i.e. mind independent reality underlying appearances). Kant's system also affirms the reality of a free truly existent
self and of a God, which he sees as being possible because the non-temporal nature of the thing-in-itself allows for a radical freedom and genuine spontaneity. Thus, according to Kant, space and time can never represent any "property at all of any things in themselves nor any relations of them to each other, i.e., no determination of them that attaches to objects themselves and that would remain even if one were to abstract from all subjective conditions of intuition" (CPuR A 26/B 42).Throughout his career, Kant labored to distinguish his philosophy from metaphysical idealism, as some of his critics charged him with being a Berkeleyian idealist. In the second edition of his
Critique, he even inserted a "refutation of idealism". For Kant, "the perception of this persistent thing is possible only through a thing outside me and not through the mere representation of a thing outside me."
Neo-Kantianism Kant's philosophy was extremely influential on European
enlightenment thinkers (and
counter-enlightenment ones as well), and his ideas were widely discussed and debated. Transcendental idealism was also defended by later
Kantian philosophers who adopted his method, such as
Karl Leonhard Reinhold and
Jakob Sigismund Beck. The mid-19th century saw a revival of Kantian philosophy, which became known as
Neo-Kantianism, with its call of "Back to Kant". This movement was especially influential on 19th century German academic philosophy (and also continental philosophy as a whole). Some important figures include:
Hermann Cohen (1842–1918),
Wilhelm Windelband (1848–1914),
Ernst Cassirer,
Hermann von Helmholtz,
Eduard Zeller,
Leonard Nelson,
Heinrich Rickert, and
Friedrich Albert Lange. A key concern of the Neo-Kantians was to update Kantian epistemology, particularly in order to provide an epistemic basis for the modern sciences (all while avoiding ontology altogether, whether idealist or materialist). Neo-Kantianism influenced the work of the
Vienna circle and its ambassadors to the Anglophone world,
Rudolf Carnap (1891–1970) and
Hans Reichenbach. Though heavily drawing on Kant, these thinkers were not transcendental idealists as such, and they sought to move beyond the idea that things in themselves are unknowable an idea they considered as opening the door to
skepticism and
nihilism. Post-Kantian German idealists thus rejected transcendental idealism by arguing against the opposition of a mind-independent world of being and a subjective world of mental constructs (or the separation between the knowledge and what is known, between subject and object, real and ideal). This new German idealism was distinguished by an "inseparability of being and thinking" and "a dynamic conception of self-consciousness" that sees reality as spontaneous conscious activity and its expressions. As such, this kind of metaphysical idealism, focused on dynamic processes and forces, was opposed to older forms of idealism, which based itself on substance theory (which these Germans labeled "dogmatism"). For Fichte, the primordial act at the ground of being is called "self-positing". Fichte argues that self-consciousness or the I is a spontaneous unconditioned self-creating act which he also called the deed-act (
tathandlung). Fichte argues that positing something unconditioned and independent at the ground of all is the only way to avoid an epistemic
infinite regress. According to Fichte, this "I am" or "absolute subject" which "originally posits its own being absolutely" (
Doctrine I, 2: 261), "is at the same time the actor and the product of the act; the actor, and that which the activity brings forth; act and deed are one and the same" (
Doctrine I, 2: 259). Fichte also argues that this "I" has the capacity to "counter-posit" a "not-I", leading to
a subject-object relationship. The I also has a third capacity Fichte calls "divisibility", which allows for the existence of plurality in the world, which however must be understood as manifestations of the "I-activity", and as being "within the I". Fichte's philosophy was adopted by Schelling who defended this new idealism as a full
monistic ontology which tried to account for all of nature which he would eventually name "absolute idealism". For Schelling, reality is an "original unity" (
ursprüngliche Einheit) or a "primordial totality" (
uranfängliche Ganzheit) of opposites. This is an absolute which he described as an "eternal act of cognition" is disclosed in subjective and objective modes, the world of ideas and nature. As such, Hegel's system is an ontological monism fundamentally based on a unity between being and thought, subject and object, which he saw as being neither materialistic realism nor subjective idealism (which still stands in an opposition to materialism and thus remains stuck in the subject-object distinction). In his
Phenomenology of Spirit (1807), Hegel provides an epistemological argument for idealism, focusing on proving the "metaphysical priority of identities over and against their opposed elements". Hegel's argument begins with his conception of knowledge, which he holds is a relation between a claim about a subject and an object that allows for a correspondence between their structural features (and is thus a type of
correspondence theory). Hegel argues that if knowledge is possible, real objects must also have a similar structure as thought (without, however, being reduced to thoughts). If not, there could be no correspondence between what the object is and what a subject believes to be true about the object. For Hegel, any system in which the subject that knows and the object which is known are structurally independent would make the relations necessary for knowledge impossible. Hegel also argues that finite qualities and objects depend on other finite things to determine them. An infinite thinking being, on the other hand, would be more self-determining and hence most fully real. Hegel argued that a careful analysis of the act of knowledge would eventually lead to an understanding of the unity of subjects and the objects in a single all-encompassing whole. In this system, experiences are not independent of the thing in itself (as in Kant) but are manifestations grounded in a metaphysical absolute, which is also experiential (but since it resists the experiential subject, can be known through this resistance). Thus, our own experiences can lead us to an insight into the thing in itself. Furthermore, since reality is a unity, all knowledge is ultimately self-knowledge, or as Hegel puts it, it is the subject being "in the other with itself" (
im Anderen bei sich selbst sein). Later, in his
Science of Logic (1812–1814), Hegel further develops a metaphysics in which the real and objective activity of thinking unfolds itself in numerous ways (as objects and subjects). This ultimate activity of thought, which is
not the activity of specific subjects, is an immediate fact, a given (
vorhandenes), which is self-standing and self-organizing. In manifesting the entire world, the absolute enacts a process of self-actualization through a grand structure or master logic, which is what Hegel calls "reason" (
Vernunft), and which he understands as a
teleological reality.
Hegelianism was deeply influential throughout the 19th century, even as some Hegelians (like
Marx) rejected idealism. Later idealist Hegelians include
Friedrich Adolf Trendelenburg (1802–72) and
Rudolf Hermann Lotze (1817–81).
Schopenhauer's philosophy The philosophy of Arthur Schopenhauer owes much to the thought of Kant and to that of the German idealists, which he nevertheless strongly criticizes. Schopenhauer maintains Kant's idealist epistemology which sees even space, time and causality as mere mental representations (vorstellungen) conditioned by the subjective mind. However, he replaces Kant's unknowable thing-in-itself with an absolute reality underlying all ideas that is a single irrational Will, a view that he saw as directly opposed to Hegel's rational Spirit. Schopenhauer argues that, even though we do experience our own bodies through the categories of space, time and causality, we also experience it in another more direct and internal way through the experience of willing. This immediate experience reveals that it is will alone which "gives him the key to his own appearance, reveals to him the meaning and shows him the inner workings of his essence, his deeds, his movements" (WWR §18, p. 124). Furthermore, since this is the only form of insight we have of the inner essence of any reality, we must apply this insight "to [the] appearances in the inorganic [and organic] world as well." Schopenhauer compares willing with many natural forces. As such, Will is "a name signifying the being in itself of every thing in the world and the sole kernel of every appearance" (WWR §23, pp. 142–3). Because irrational Willing is the most foundational reality, life is filled with frustration, irrationality and disappointment. This is the metaphysical foundation of Schopenhauer's
pessimistic philosophy of life. The best we can hope for is to deny and try to escape (however briefly) the incessant force of the Will, through art,
aesthetic experience,
asceticism, and
compassion.
Gentile's actual idealism Actual idealism is a form of idealism developed by
Giovanni Gentile which argues that reality is the ongoing act of thinking, or in Italian "pensiero pensante" and thus, only thoughts exist. He further argued that our combined thoughts defined and produced reality. Giovanni Gentile was a key supporter of
fascism, regarded by many as the "philosopher of fascism". His idealist theory argued for the unity of all society under one leader, which allows it to act as one body. During this time, the defenders of
British idealism made significant contributions to all fields of philosophy. However, other philosophers, like
McTaggart, broke from this trend and instead defended a pluralistic idealism in which the ultimate reality is a plurality of minds. Many Anglo-American idealists were influenced by
Hegelianism, but they also drew on Kant, Plato and Aristotle. Key figures of this transatlantic movement include many of the British idealists, such as
T. H. Green (1836–1882),
F. H. Bradley (1846–1924),
Bernard Bosanquet (1848–1923),
J. H. Muirhead (1855–1940),
H. H. Joachim (1868–1938),
A. E. Taylor (1869–1945),
R. G. Collingwood (1889–1943),
G. R. G. Mure (1893–1979) and
Michael Oakeshott. American idealist philosophers include
Josiah Royce (1855–1916) and
Brand Blanshard (1892–1987).
British absolute idealism , a leading British absolute idealist One of the early influential British idealists was
Thomas Hill Green, known for his posthumous
Prolegomena to Ethics. Green argues for an idealist metaphysics in this text as a foundation for free will and ethics. In a Kantian fashion, Green first argues that knowledge consists in seeing relations in consciousness, and that any sense of something being "real" or "objective" has no meaning outside of consciousness. He then argues that experience as consciousness of related events "cannot be explained by any natural history, properly so called" and thus "the understanding which presents an order of nature to us is in principle one with an understanding which constitutes that order itself." Green then further argues that individual human beings are aware of an order of relations which extends beyond the bounds of their individual mind. For Green, this greater order must be in a larger transpersonal intelligence, while the world is "a system of related facts" which is made possible and revealed to individual beings by the larger intelligence. Furthermore, Green also holds that participation in the transpersonal mind is constituted by the apprehension of a portion of the overall order by animal organisms. This absolute reality "is one system, and ... its contents are nothing but sentient experience. It will hence be a single and all-inclusive experience, which embraces every partial diversity in concord." Bradley presented his idealism in his
Appearance and Reality (1893) by arguing that the ideas we use to understand reality are contradictory. He deconstructs numerous ideas including primary and secondary qualities, substances and attributes, quality and relation, space, time and causality and the self. Most famously, Bradley argued that any ultimate distinction between qualities and relations is untenable since "qualities are nothing without relations" since "their plurality depends on relation, and, without that relation, they are not distinct. But, if not distinct, then not different, and therefore not qualities." Even though all appearances are "not truth", it is still possible to have true knowledge of ultimate reality, which must be a unity beyond contradictions but which still allows for diversity. Bradley thinks that this character of reality as a diverse unity is revealed to us in sentient experience, since our various experiences must be grounded and caused by some undifferentiated and pre-abstract reality. However he also admits "our complete inability to understand this concrete unity in detail".
American idealism Idealism also became popular in the United States with thinkers like
Charles Sanders Peirce (1839–1914), who defended an "objective idealism" in which, as he put it, "matter is effete mind, inveterate habits becoming physical laws". Peirce initially defended a type of
representationalism alongside his form of
Pragmatism which was metaphysically neutral since it is "no doctrine of metaphysics". However, in later years (after c.1905), Peirce defended an objective idealism which held that the universe evolved from a state of maximum spontaneous freedom (which he associated with mind) into its present state where matter were merely "congealed" mind. In arguing for this view, he followed the classic idealist premise that states there must be a metaphysical equality (an
isomorphism) between thought and being, and as such, "the root of all being is One". A key feature of Peirce's idealism is "
Tychism", which he defined as "the doctrine that absolute chance is a factor of the universe." This allows for an element of chance or
indeterminism in the universe which allows for cosmological evolution. Under the influence of Peirce, it was
Josiah Royce (1855–1916) who became the leading American idealist at the turn of the century. Royce's idealism incorporated aspects of Peirce's Pragmatism and is defended in his
The Spirit of Modern Philosophy (1892). One of Royce's arguments for idealism is his argument from meaning, which states the possibility of there being
meaning at all requires an identity between what is meant (ordinary objects) and what makes meaning (ordinary subjects). In his
The World and the Individual (2 vols, 1899 and 1901), Royce also links meaning with purpose, seeing the meaning of a term as its intended purpose. Royce was an absolute idealist who held that ultimately reality was a super-self, an absolute mind. Royce argues that for a mind to be able represent itself and its representations (and not lead to a vicious infinite regress), it must be complex and capacious enough, and only an absolute mind has this capacity. His idealism is most obvious in
The Nature of Thought (1939), where he discusses how all
perception is infused with concepts. He then argues from a
coherence theory of truth that the "character of reality" must also include coherence itself, and thus, knowledge must be similar to what it knows.
Pluralistic idealism Pluralistic idealism takes the view that there are many individual minds,
monads, or processes that together underlie the existence of the observed world and which make possible the existence of the physical universe. Pluralistic idealism does not assume the existence of a single ultimate mind or absolute as with the total
monism of absolute idealism, instead it affirms an ultimate plurality of ideas or beings.
Personalism Personalism is the view that the individual minds of persons or selves are the basis for ultimate reality and value and as such emphasizes the fundamentality and inherent worth of persons. Modern personalist idealism emerged during the reaction against what was seen as a dehumanizing impersonalism of absolute idealism, a reaction which was led by figures like
Hermann Lotze (1817–1881). American personalism was particularly associated with idealism and with
Boston university, where Bowne (who had studied with Lotze) developed his personalist idealism and published his
Personalism (1908). Howison, in his book
The Limits of Evolution and Other Essays Illustrating the Metaphysical Theory of Personal Idealism, developed a democratic idealism that extended all the way to God, who instead of a monarch, was seen as the ultimate democrat in eternal relation to other eternal persons. Another pluralistic idealism was
Thomas Davidson's (1840–1900) "
apeirotheism", which he defined as "a theory of Gods infinite in number". The theory was indebted to
Aristotle's view of the eternal rational soul and the
nous. 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. Another influential British idealist,
J. M. E. McTaggart (1866–1925), defended a theory in which reality is a community of individual spirits connected by the relation of love. McTaggart defends ontological idealism through a
mereological argument which argues only spirits can be substances, as well as through an argument for the unreality of time (a position he also defends in
The Unreality of Time). For example, the existence of matter cannot be inferred based on sensations, since they cannot be divided to infinity (and thus cannot be substances). Spirits on the other hand are true infinitely divisible substances. They have "the quality of having content, all of which is the content of one or more selves", and know themselves through direct perception as substances persisting through time. For McTaggart, there is a multiplicity of spirits, which are nevertheless related to each other harmoniously through their love for each other.
Contemporary idealism wrote that "the Universe begins to look more like a great thought than like a great machine." Today, idealism remains a minority view in Western analytic circles. Several modern figures continue to defend idealism. Recent idealist philosophers include
A. A. Luce (
Sense without Matter, 1954),
Timothy Sprigge (
The Vindication of Absolute Idealism, 1984),
Leslie Armour,
Vittorio Hösle (
Objective Idealism, 1998),
John Andrew Foster (
A World for Us, 2008),
John A. Leslie (
Infinite Minds: A Philosophical Cosmology, 2002), and
Bernardo Kastrup (
The Idea of the World, 2018). In 2022,
Howard Robinson authored
Perception and Idealism. Both Foster and Sprigge defend idealism through an epistemic argument for the unity of the act of perception with its object. Sprigge also made an argument from
grounding, which held that our phenomenal objects presuppose some
noumenal ground. As such For Sprigge, the physical world "consists in innumerable mutually interacting centres of experience, or, what comes to the same, of pulses and flows of experience."
Analytic idealism A recent strand of idealist metaphysics has been developed within analytic philosophy (
analytic idealism) by Bernardo Kastrup. In his doctoral dissertation
Analytic Idealism (2019), he argues that reality is constituted by universal consciousness and introduces the notion of dissociation as a mechanism to explain how individual conscious agents arise within a single underlying mind. His later work
Analytic Idealism in a Nutshell has been the subject of reviews and discussion in contemporary philosophy (e.g. Sjöstedt-Hughes 2025). Building on this approach, Bruno Tonetto's
Return to Consciousness (2025) synthesizes consciousness-first arguments from science, metaphysics, and cultural analysis, presenting idealism as a unifying worldview. These contributions exemplify a small but ongoing effort to revive idealist metaphysics in analytic philosophy of mind.
Idealistic theories based on 20th-century science 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.
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." 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. ==Criticism==