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General Bibliography of Idealists


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Idealism is the doctrine that ideas, or thought, make up either the whole or an indispensable aspect of any full reality, so that a world of material objects containing no thought either could not exist as it is experienced, or would not be fully "real." Idealism is often contrasted with materialism, both belonging to the class of monist as opposed to dualist or pluralist ontologies. (Note that this contrast between idealism and materialism has to do with the question of the nature of reality as such - it has nothing to do with advocating high moral standards, or the like.) Subjective Idealists and Phenomenalists (such as George Berkeley) hold that minds and their experiences constitute existence. Transcendental Idealists (such as Immanuel Kant) argue from the nature of knowledge to the nature of the objects of knowledge--without suggesting that those objects are composed of ideas or located in the knower’s mind. Objective Idealists hold either that there is ultimately only one perceiver, who is identical with what is perceived (this is the doctrine of Josiah Royce), or that thought makes possible the highest degree of self-determination and thus the highest degree of reality (this is G.W.F. Hegel’s Absolute Idealism). Panpsychists (such as Leibniz) hold that all objects of experience are also subjects. That is, plants and minerals have subjective experiences--though very different from the consciousness of animals.

Idealism in general is the metaphysical doctrine sketched in the previous paragraph. A separate doctrine, epistemological idealism (also known as the "way of ideas"), asserts that minds are aware of or perceive only their own ideas, and not external objects. This was held by (for example) John Locke, who was certainly not a metaphysical idealist. Berkeley’s argument for his metaphysical idealism was indeed built around the difficulties in Locke’s epistemological position. But other influential metaphysical idealisms, such as those of Plotinus, Leibniz, and Hegel, are not based primarily on epistemological considerations. So "idealism" in general--that is, metaphysical idealism--should not be defined in a way that makes it depend on epistemological considerations.

The approach to idealism by Western philosophers has been different from that of Eastern thinkers. In much of Western thought (though not in such major Western thinkers as Plato and Hegel ) the ideal relates to direct knowledge of subjective mental ideas, or images. It is then usually juxtaposed with realism in which the real is said to have absolute existence prior to and independent of our knowledge. Epistemological idealists (such as Kant) might insist that the only things which can be directly known for certain are ideas. In Eastern thought, as reflected in Hindu idealism, the concept of idealism takes on the meaning of higher consciousness, essentially the living consciousness of an all-pervading God, as the basis of all phenomena. A type of Asian idealism is Buddhist idealism.


Idealism names a number of philosophical positions with quite different tendencies and implications.

Idealism in the West


In his chief work Truth, Antiphon wrote: "Time is a thought or a measure, not a substance". This presents time as an ideational, internal, mental operation, rather than a real, external object.


Main article: Platonic idealism

In common discussion, Plato is often referred to as an "idealist," because of his doctrine of the "Forms," which are certainly "ideals," in a broad sense. But Plato doesn’t describe the Forms as being in any mind. Instead, he regularly describes them as having their own, independent existence. So it seems clear that Plato is not, at any rate, a "subjective" idealist, like Berkeley.

Plato’s Allegory of the Cave is sometimes interpreted as drawing attention to the problem of knowing "external objects"--the problem that concerned Descartes, Locke, Berkeley, and other modern philosophers. But the Forms that the Cave-dwellers are ignorant of aren’t "external" to them in the way that material objects are for these modern thinkers. The Forms are the true realities, but they aren’t spatially outside us, as material objects are. So the issue that Plato’s allegory addresses--which is, roughly, how can we know what is truly real (and truly good)?--is quite different from the modern issue of our knowledge of the "external world."

However, even if Plato doesn’t share the specific concerns of modern philosophy, and of George Berkeley, in particular, Plato could still be a non-subjective idealist. He could believe that matter has no independent existence, or that full "reality" (as distinct from mere existence) is achieved only through thought. Bernard Williams and Myles Burnyeat have maintained that Greek philosophers never conceived of idealism as an option, because they lacked Descartes’s conception of an independently existing mind. But Williams and Burnyeat didn’t consider the possibility that Plato could have held an idealism like Kant’s, which argues from the nature of knowledge to the nature of the objects of knowledge, or like Hegel’s, which denies that matter is fully "real"--without (in either case) reducing material objects to ideas in a mind or minds.

The German Neo-Kantian scholar, Paul Natorp, argued in his Plato’s Theory of Ideas. An Introduction to Idealism (first published in 1903) that Plato was a non-subjective, "transcendental" idealist, somewhat like Kant, and Natorp’s thesis has received support from some recent scholars.


Schopenhauer wrote of this Neoplatonist philosopher: "With Plotinus 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 (Enneads, iii, lib. vii, c.10) that the soul has made the world by stepping from eternity into time, with the explanation: ’For there is for this universe no other place than the soul or mind’ (neque est alter hujus universi locus quam anima), indeed the ideality of time is expressed in the words: ’We should not accept time outside the soul or mind’ (oportet autem nequaquam extra animam tempus accipere)." (Parerga and Paralipomena, Volume I, "Fragments for the History of Philosophy," § 7)

Similarly, professor Ludwig Noiré wrote: "For the first time in Western philosophy we find idealism proper in Plotinus (Enneads, iii, 7, 10), where he says, "The only space or place of the world is the soul," and "Time must not be assumed to exist outside the soul." It is worth noting, however, that like Plato but unlike Schopenhauer and other modern philosophers, Plotinus does not worry about whether or how we can get beyond our ideas in order to know external objects.


Writing about Descartes, Schopenhauer claimed, ".. he was the first to bring to our consciousness the problem whereon all philosophy has since mainly turned, namely that of the ideal and the real. This is the question concerning what in our knowledge is objective and what subjective, and hence what eventually is to be ascribed by us to things different from us and what is to be attributed to ourselves." (Parerga and Paralipomena, Vol. I, "Sketch of a History of the Doctrine of the Ideal and the Real")

According to Descartes, we really know only what is in our own consciousnesses. We are immediately and directly aware of only our own states of mind. The whole external world is merely an idea or picture in our minds. Therefore, it is possible to doubt the reality of the external world as consisting of real objects. "I think, therefore I am" is the only assertion that can’t be doubted. This is because self-consciousness and thinking are the only things that are unconditionally experienced for certain as being real. In this way, Descartes posed the issue of epistemological idealism, which is awareness of the difference between the world as an ideational mental picture and the world as a system of external objects.


Malebranche a student of the Cartesian School of Rationalism disagreed that if the only things that we know for certain are the ideas within our mind, then the existence of the external world would be dubious and known only indirectly. He declared instead that the real external world is actually God. All activity only appears to occur in the external world. In actuality, it is the activity of God. For Malebranche, we directly know internally the ideas in our mind. Externally, we directly know God’s operations. This kind of idealism led to the pantheism of Spinoza.


Leibniz expressed a form of Idealism known as Panpsychism in his theory of monads, as exposited in his Monadologie . He held Monads are the true atoms of the universe, and are also entities having sensation. The monads are "substantial forms of being" They are indecomposable, individual, subject to their own laws, un-interacting, and each reflecting the entire universe. Monads are centers of force; substance is force, while space, matter, and motion are phenomenal. For Leibniz, there is an exact pre-established harmony or parallel between the world in the minds of the alert monads and the external world of objects. God, who is the central monad, established this harmony and the resulting world is an idea of the monads’ perception. In this way, the external world is ideal in that it is a spiritual phenomenon whose motion is the result of a dynamic force. Space and time are ideal or phenomenal and their form and existence is dependent on the simple and immaterial monads. Leibniz’s cosmology, with its central monad, embraced a traditional Christian Theism and was more of a Personalism than the naturalistic Pantheism of Spinoza.

George Berkeley

Bishop Berkeley, in seeking to find out what we could know with certainty, decided that our knowledge must be based on our perceptions. This led him to conclude that there was indeed no "real" knowable object behind one’s perception, that what was "real" was the perception itself. This is characterised by Berkeley’s slogan: "Esse est aut percipi aut percipere" or "To be is to be perceived or to perceive", meaning that something only exists, in the particular way that it is seen to exist, when it is being perceived (seen, felt etc.) by an observing subject.

This subjective idealism or dogmatic idealism led to his placing the full weight of justification on our perceptions. This left Berkeley with the problem of explaining how it is that each of us apparently has much the same sort of perceptions of an object. He solved this problem by having God intercede, as the immediate cause of all of our perceptions.

Schopenhauer wrote: "Berkeley was, therefore, the first to treat the subjective starting-point really seriously and to demonstrate irrefutably its absolute necessity. He is the father of idealism...." (Parerga and Paralipomena, Vol. I, "Fragments for the History of Philosophy," § 12) Schopenhauer could have said, instead, that Berkeley was the "father" of the modern variety of idealism that is motivated, primarily, by epistemological considerations--as distinct from the more purely metaphysical idealism of (for example) Plotinus or Hegel. Bishop Berkeley therefore is considered the first modern philosopher known as an idealist. His immaterialism held that objects exist by the good quality of our perception of them. In other words, they are ideas residing in our awareness - as well as in the consciousness of the Divine Being.

Arthur Collier

Arthur Collier published the same assertions that were made by Berkeley. However, there seemed to have been no influence between the two contemporary writers. Collier claimed that the represented image of an external object is the only knowable reality. Matter, as a cause of the representative image, is unthinkable and therefore nothing to us. An external world, as absolute matter, unrelated to an observer, does not exist for human perceivers. As an appearance in a mind, the universe cannot exist as it appears if there is no perceiving mind.

Collier was influenced by John Norris’s (1701) An Essay Towards the Theory of the Ideal or Intelligible World. The idealist statements by Collier were generally dismissed by readers who were not able to reflect on the distinction between a mental idea or image and the object that it represents.

Jonathan Edwards

Jonathan Edwards, an American theologian, went to Yale University in 1716 at the age of thirteen. After reading Locke’s doctrine of ideas, he kept a notebook entitled "Mind." In it, he wrote, at the age of fourteen, that the only things that are real are minds. He contended that matter exists only as an idea in a mind. Due to his theological manner of thinking, he asserted that space is God, due to its infinity. After adolescence, he never elaborated on these early idealistic notes.

Immanuel Kant

Immanuel Kant held that the mind shapes the world as we perceive it to take the form of space-and-time. Kant focused on the idea drawn from British empiricism (and its philosophers such as Locke, Berkeley, and Hume) that all we can know is the mental impressions, or phenomena, that an outside world, which may or may not exist independently, creates in our minds; our minds can never perceive that outside world directly. Kant emphasized the difference between things as they appear to an observer and things in themselves, "... that is, things considered without regard to whether and how they may be given to us... "

... if I remove the thinking subject, the whole material world must at once vanish because it is nothing but a phenomenal appearance in the sensibility of ourselves as a subject, and a manner or species of representation. - Critique of Pure Reason A383

Kant’s postscript to this added that the mind is not a blank slate (contra John Locke), but rather comes equipped with categories for organising our sense impressions. This Kantian sort of idealism opens up a world of abstractions (i.e., the universal categories minds use to understand phenomena) to be explored by reason, but in sharp contrast to Plato’s, confirms uncertainties about a (un)knowable world outside our own minds. We cannot approach the noumenon, the "Thing in Itself" (German: Ding an Sich) outside our own mental world. (Kant’s idealism goes by the counterintuitive name of transcendental idealism.) Kant distinguished his transcendental or critical idealism from previous varieties:

The dictum of all genuine idealists, from the Eleatic school to Bishop Berkeley, is contained in this formula: "All knowledge through the senses and experience is nothing but sheer illusion, and only in the ideas of the pure understanding and reason is there truth." The principle that throughout dominates and determines my idealism is, on the contrary: "All knowledge of things merely from pure understanding or pure reason is nothing but sheer illusion, and only in experience is there truth." - Prolegomena, 374


Johann Fichte denied Kant’s noumenon, and made the claim that consciousness made its own foundation, that the mental ego of the self relied on no external, and that an external of any kind would be the same as admitting a real material. He was the first to make the attempt at a presuppositionless theory of knowledge, wherein nothing outside of thinking would be assumed to exist outside the initial analysis of concept. So that conception could be solely grounded in itself, and assume nothing without deduction from there first, what he called a Wissenschaftslehre. (This stand is very similar to Giovanni Gentile’s Actual Idealism, except that Gentile’s theory goes further by denying a ground for even an ego or self made from thinking.)


Hegel, another philosopher whose system has been called idealism, argued in his Science of Logic (1812-1814) 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 would have a better claim to be called fully real. Similarly, finite natural things are less "real"--because they’re 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 merely natural objects are fully real, is mistaken. Hegel called his philosophy absolute idealism, in contrast to the "subjective idealism" of Berkeley and the "transcendental idealism" of Kant and Fichte, which were not based (like Hegel’s idealism) on a critique of the finite. The "idealists" listed above whose philosophy Hegel’s philosophy most closely resembles are Plato and Plotinus. None of these three thinkers associates their idealism with the epistemological thesis that what we know are "ideas" in our minds.

It is a noteworthy fact that many commentators on Hegel, and even some who admire Hegel’s philosophy, fail to distinguish his type of idealism from Berkeley’s and Kant’s. Hegel certainly intends to preserve what he takes to be true in Kant’s idealism, in particular Kant’s insistence that ethical reason can and does go beyond finite "inclinations". But Hegel doesn’t endorse Kant’s conception of the "thing-in-itself," or the type of epistemological argument that led Kant to that conception. Still less does Hegel endorse Berkeley’s notion that things exist only by being perceivers or being perceived.

The guiding idea behind Hegel’s "absolute idealism" is the observation, which he shares with Plato, that the exercise of reason enables the reasoner to achieve a kind of reality (namely, self-determination, or reality as oneself) that mere physical objects like rocks can’t achieve. By giving this observation a central role in his thinking, Hegel contributes to a philosophical tradition, beginning with Plato, that has been obscured by the modern preoccupation with the epistemological problem of the subject’s access to the "external world."


In the first volume of his Parerga and Paralipomena, Schopenhauer wrote his "Sketch of a History of the Doctrine of the Ideal and the Real". He defined the ideal as being mental pictures that 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. Schopenhauer emphasized that we are restricted to our own consciousness. The world that appears is only a representation or mental picture of objects.

We directly and immediately know only representations. All objects that are external to the mind are known indirectly through the mediation of our mind. Schopenhauer’s history is an account of the concept of the "ideal" in its meaning as "ideas in a subject’s mind." In this sense, "ideal" means "ideational" or "existing in the mind as an image." He does not refer to the other meaning of "ideal" as being qualities of the highest perfection and excellence. In his On the Freedom of the Will, Schopenhauer noted the ambiguity of the word "idealism" by calling it a "term with multiple meanings."

True philosophy must at all costs be idealistic; indeed, it must be so merely to be honest. For nothing is more certain than that no one ever came out of himself in order to identify himself immediately with things different from him; but everything of which he has certain, sure, and therefore immediate knowledge, lies within his consciousness. Beyond this consciousness, therefore, there can be no immediate certainty... There can never be an existence that is objective absolutely and in itself; such an existence, indeed, is positively inconceivable. For 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. - The World as Will and Representation, Vol. II, Ch. 1

It is evident that Schopenhauer’s "idealism" is based primarily on considerations having to do with the relation between our ideas and external reality, rather than being based (like Plato’s, Plotinus’s, or Hegel’s "idealism") on considerations having to do with the nature of reality as such.

British idealism

British idealism enjoyed ascendancy in English-speaking philosophy in the later part of the 19th century. F. H. Bradley of Merton College, Oxford, saw reality as a monistic whole, which is apprehended through "feeling", a state in which there is no distinction between the perception and the thing perceived. Like Berkeley, Bradley thought that nothing can be known to exist unless it is known by a mind.

We perceive, on reflection, that to be real, or even barely to exist, must be to fall within sentience... Find any piece of existence, take up anything that any one could possibly call a fact, or could in any sense assert to have being, and then judge if it does not consist in sentient experience. Try to discover any sense in which you can still continue to speak of it, when all perception and feeling have been removed; or point out any fragment of its matter, any aspect of its being, which is not derived from and is not still relative to this source. When the experiment is made strictly, I can myself conceive of nothing else than the experienced.

F.H. Bradley, ’Appearance and Reality’, Chapter 14

Bradley was the apparent target of G. E. Moore’s radical rejection of idealism. Moore claimed that Bradley did not understand the statement that something is real. We know for certain, through common sense and prephilosophical beliefs, that some things are real, whether they are objects of thought or not, according to Moore. In this way, he disagreed with Bradley’s assertion that we cannot think of anything that really exists unless we have a thought of it in our mind.

J. M. E. McTaggart of Cambridge University, argued that minds alone exist, and that they only relate to each other through love. Space, time and material objects are for McTaggart unreal. He argued, for instance, in The Unreality of Time that it was not possible to produce a coherent account of a sequence of events in time, and that therefore time is an illusion. His book The Nature of Experience (1927) contained his arguments that space, time, and matter cannot possibly be real. In his Studies in Hegelian Cosmology, Cambridge, 1901, p. 196, 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?

American philosopher Josiah Royce described himself as an objective idealist.

Karl Pearson

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 " 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."