Leibniz's Question, the Crisis of Physicalism, and the Return of Absolute Idealism

Introduction
A recurrent theme on this blog is the idea that we need some notion of self-causation in order to answer Leibniz’s famous question: “Why is there something rather than nothing?” If we define “reality” as the totality of what exists (including past and future existence), then by definition nothing exists outside of reality (not even ‘the nothing’). If we then presuppose the Principle of Sufficient Reason – that there is a sufficient reason for every fact, including the fact that reality exists – then it follows that the reason for reality’s existence must lie within reality itself, since there is nothing outside of it. And since we generally call the reason why something exists the cause of that something, we must conclude that reality has to be self-causing.

G.W. Leibniz (1646-1716)

In this post I will investigate this mysterious notion – the self-causation of reality – in light of the current crisis of materialism or what is nowadays rather known as physicalism, i.e. the ontology that takes (completed) physics as the final description of reality. It is a well-known fact that physicalism is presently under increasing attack, mainly by philosophers who point out the irreducibility of consciousness to a physicalist framework. Since self-causation is generally deemed impossible on a physicalist framework, the present crisis of physicalism means that the notion of self-causation gets a second chance.

Moreover, since it is consciousness which is largely responsible for bringing on this crisis of physicalism, the question arises whether consciousness is perhaps the key to understanding the self-causation of reality. This takes us in the direction of Absolute Idealism, where the self-causing essence of reality is generally conceived of in terms of self-consciousness. Thus Absolute Idealism can be broadly summarized as the claim that reality exists because it is thought and/or experienced by an Absolute Mind, which in turn exists because It thinks/experiences itself. It is through its self-consciousness, therefore, that the Absolute Mind lifts itself into existence – at least according to such Absolute-Idealist thinkers such Plotinus, Shankara, Fichte, Schelling, Hegel and Royce.

In the final sections of this post I will discuss two common mistakes about Absolute Idealism: (1) that Absolute Idealism was first and foremost a creature of the 19th century, invented by post-Kantian German Idealists (Fichte, Schelling and above all Hegel) and then passed on to Anglo-American Idealists (Green, Bradley, McTaggart, Royce); and (2) that Absolute Idealism was refuted at the beginning of the 20th century by the founding fathers of Analytic Philosophy, Russell and Moore, as well as by empirical science, and that Absolute Idealism has henceforth become obsolete. Both mistakes will be corrected by taking a closer look, firstly, at the millennia-old history of Absolute Idealism in both Eastern and Western philosophy and, secondly, at the remarkable return of Absolute-Idealist themes in contemporary Analytic Philosophy and physics.

Plotinus: The originator of self-causation in Western philosophy
As noted in the Introduction, we need the notion of self-causation in order to answer Leibniz’s famous question: “Why is there something rather than nothing?” Since there is nothing outside of reality as a whole, the reason for its existence can only lie within reality itself. In that sense, then, reality must be self-causing. This argument is nothing new and I certainly claim no originality for it. It has ancient roots in Western philosophy, going back as far as Plotinus, who appears to have been the very first Western philosopher to speak of God (or rather the One in Plotinian terminology) as self-caused (cf. Gerson 2011: 34). Thus, to underscore the self-causing nature of the One, Plotinus says that “it itself makes itself [...] from nothing” (Ennead VI, 8, 7).

Plotinus (ca. 204/5-270)
introduced the notion of
self-causation in Western
philosophy

Clearly, Plotinus does not mean here that the One has literally emerged out of nothing, as if at first there was nothing and then suddenly the One sprang into existence, like a ‘hiccup from the void’. Plotinus surely agreed with the supremely Greek principle that from nothing only nothing can come (ex nihilo nihil fit), which is precisely the reason why reality can ultimately come only from itself, such that we must postulate self-causation at the origin of reality. So when Plotinus says that the One makes itself “from nothing”, what he means is that nothing preceded the One (not even ‘nothing’), because the One is the all-inclusive reality. “The One is all things,” Plotinus writes, which is precisely the reason why the One qua “really existent All is in nothing; for there is nothing before it” (Enneads V, 2, 1 & VI, 4, 2). The One, then, is for Plotinus the self-causing core of all-inclusive reality, which must be self-causing precisely because there is nothing outside of it.

Physicalism and the fig-leaf conception of self-causation
From Plotinus this argument for a self-causing core to reality – what Pascal called “the God of the philosophers” – found its way to later philosophers, notably premodern and early modern philosophers such as Augustine, Descartes and Spinoza. In still later philosophers, however, we see this notion of self-causation gradually disappearing from view – even in philosophers who agree with the argument motivating this notion, namely, the argument that reality must contain the reason for its own existence, since there is nothing outside of it.

John Leslie (1940-), one of the few
contemporary philosophers who
still use the notion of self-causation

Thus we see modern philosophers who agree with this argument use all kinds of fig-leaf conceptions of self-causation, i.e. euphemistic concepts that basically mean the same thing but sound ‘less offensive’ – concepts such as “explanatory self-subsumption” (Nozick), “self-explanation” (Rescher), “cosmic bootstrapping” (Atkins), and “self-excitation / self-synthesis” (Wheeler). (A notable exception, however, is John Leslie who, as a Neoplatonizing Spinozist, is quite happy to invoke self-causation.)

Why this dread of self-causation, when the point these thinkers wish to make – that the reason for reality's existence can only lie within it – clearly invites that notion? The reason behind this dread, I venture, lies in the rise of physicalism as the dominant ontology of the modern age. I define “physicalism” as the ontology that takes reality to be primarily physical reality as described by mathematical-experimental physics. The truth of physicalist ontology has seemed – please note the past tense! – almost self-evident in light of the stunning experimental successes of modern physics (from classical mechanics to relativity and quantum theory). Physicalism was further reinforced by the victory of Neo-Darwinism, which seems to show that our consciousness is ‘just’ an evolutionary product of mechanical processes of molecular reproduction and natural selection.

Due to the resulting dominance of physicalism, the concept of causation became virtually synonymous with “physical causation”. One could say that of the rich Aristotelian array of four types of causality – formal, material, final and efficient – only one survived: a denuded notion of efficient causality, limited to the physical realm and restricted by the mathematical laws uncovered by physics. But if physical causation is the only form of causation around, then obviously self-causation doesn't make much sense. Physical reality is essentially spatiotemporal, and – as I have argued extensively in my previous post – self-causation is impossible in time (so if reality has a self-causing cause, the latter must be atemporal).

This is the main reason why modern thinkers avoid the notion of self-causation (even when agreeing with the general idea behind it), the reason being their – conscious or unconscious – acceptance of physicalism as the dominant ontology of our age. Modern science and philosophy have become so saturated with physicalism that self-causation has literally become unthinkable in current modes of thinking.

The crisis of physicalism
As noted, however, the truth of physicalism has seemed almost self-evident – meaning that this is now no longer the case. The truth of physicalism as a general ontology is increasingly put into doubt by both philosophers and scientists. It seems fair to speak of a growing crisis of physicalism, mainly brought on by the troublesome phenomenon of consciousness.

The crisis stems partly from developments internal to physics, notably the notorious measurement problem in quantum mechanics and the curious role the latter accords to the conscious choices made by observer (cf. Rosenblum & Kuttner 2011). This does not mean, of course, that the truth value of physics is being questioned, which would be absurd in light of the tremendous experimental success of modern physics (especially quantum mechanics). But the assumption, which once seemed self-evident to an earlier generation, that physics is the natural ally of physicalism, is increasingly put into question.

David Chalmers (1966-) pioneered
the Hard Problem of Consciousness

But the ontological meaning of quantum mechanics is notoriously hard to interpret (let alone its relation to consciousness), so the case of quantum mechanics has certainly not been decisive in bringing on the crisis of physicalism. Mostly, therefore, this crisis stems from purely philosophical work done on the so-termed “Hard Problem of Consciousness”, i.e. the conceptual impossibility to explain consciousness fully in physical terms. Over the past few decades various strong conceptual arguments for this explanatory irreducibility of consciousness have been developed, notably the “knowledge argument” and the “conceivability argument” (cf. Chalmers 1996).

As a result, the philosophical landscape has changed dramatically, from a thoroughly physicalist one, where consciousness was accorded no independent status apart from the physical, to a much more ambiguous landscape with different philosophical positions stressing the ontological independence of consciousness – positions such as (Substance and Property) Dualism, Russellian Monism, Panpsychism, Panprotopsychism, Idealist Monism, etc.

The renewed relevance of Absolute Idealism
But if this is so, if the ruling days of physicalism are over, then perhaps the notion of self-causation can get a second chance? If consciousness is not reducible to the physical, then obviously there must be a strictly mental form of causation, i.e. a type of causality that is intrinsic to consciousness alone. After all, even if irreducible to the physical, consciousness remains ruled by causality: stimulation of the senses generally causes sensory perceptions, perceptions cause emotional and cognitive reactions, one thought leads to another, bodily movements follow upon exertions of the will, etc. Thus, given the irreducibility of consciousness, we must admit the existence of mental causation as irreducible to physical causation. But then the question arises: does mental causation allow us to make sense of the self-causation needed to explain reality as a whole?

To this question the philosophical tradition of Absolute Idealism answers with a resounding “Yes”. To see why, let us note its central claim, which – although worked out differently by different thinkers – can be summarized as follows: everything exists because it is thought and/or experienced by an Absolute Mind, which in turn exists because It thinks/experiences Itself. Thus the Absolute Mind lifts itself into existence (is causa sui, as philosophers up to Spinoza would say) by being aware of itself. This notion of an Absolute Self-Awareness as the self-causing cause of all reality is the central thread running through the millennia-old tradition of Absolute Idealism, the thread that ties together various philosophers who are sometimes separated by continents and millennia.

Josiah Royce (1855-1916)
carried the tradition of
Absolute Idealism into
the 20th century

Thus e.g. the Vedantic sages of the Upanishads: “Brahman, indeed, was this in the beginning. It knew itself only as ‘I am Brahman’. Therefore it became all.” (Radhakrishnan 1953: 168) Thus Plotinus: “The One [...] made itself by an act of looking at itself. This act of looking at itself is [...] its being.” (Ennead VI, 8, 16, 19-21) Thus Schelling: “[I]t is through the self's own knowledge of itself that that very self first comes into being.” (Schelling 1800 [2001]: 27) Thus Royce: “[I]f whatever exists, exists only as known, then the existence of knowledge itself must be a known existence, and can finally be known only to the final knower himself, who, like Aristotle's God, is so far defined in terms of absolute self-knowledge.” (Royce 1899 [1959]: 400) Prompted by the tradition of Absolute Idealism, therefore, our question becomes: does self-awareness furnish us with a form of mental causation that amounts to self-causation?

The self-causing capacity of self-awareness
Why should self-awareness be seen as self-causing? The answer given by the various Absolute Idealists, even if it often remains largely implicit, is nevertheless clear: the self-aware subject essentially is its own object of awareness, and therefore it only exists insofar as it is aware of itself. In other words: its existence is its awareness of itself. So, by being aware of itself, it bootstraps itself into existence. Adapting Berkeley’s famous formula “esse est percipi”, we can say that the esse of self-awareness is its percipi per se – that is: its being is its being perceived by itself. This does not mean, of course, we should accept Berkeleyan idealism tout court, only that Berkeley’s formula is especially well-suited to clarify the nature of self-awareness: its existence through self-perception (here, obviously, I presuppose that awareness of something is a kind of perception – but this is largely a verbal issue).

We should, however, beware not to extend this self-producing capacity of self-awareness to its empirical properties. As an empirical individual, I am aware of myself as a physical organism, with a particular name, a social identity, having all kinds of thoughts and feelings, etc. But surely my awareness of myself as having those properties does not imply my having created them. My self-awareness does not imply my being self-caused as an empirical individual. Empirically, I exist to a large extent independently from the awareness I have of myself. The self-causing capacity of self-awareness, then, can apply only to the non-empirical aspect of self-awareness, or what I call pure self-awareness.

In order to uncover this pure self-awareness, consider the fact that to be truly self-aware it is not enough that you are aware of your empirical properties, what your body looks like, what you are doing right now, etc. To be truly self-aware, you must also be aware of the fact that you are self-aware. That is: self-awareness must itself be one of the objects of which it is aware. This follows from the essence of self-awareness, since “a self-awareness unaware of itself” is clearly a contradiction in terms. Self-awareness, then, must have a circular structure: it must include self-awareness of self-awareness. This is what I mean by “pure self-awareness”. Note that the essential circularity of pure self-awareness fits the circularity required for self-causation hand in glove: just as the self-causing cause must be its own effect, so pure self-awareness must be its own object of awareness.

Is pure self-awareness
self-producing?

The wager of Absolute Idealism is that this is much more than just a vague analogy between two circularizes: it is an intrinsic connection, an essential identity. After all: pure self-awareness cannot exist without being aware of itself. This circularity, therefore, constitutes a necessary condition for the existence of pure self-awareness. And, clearly, it is also a sufficient condition for that existence, since if there is an awareness that is its own object of awareness, then that awareness ipso facto amounts to self-awareness (however empty and lacking in empirical properties it may otherwise be). Thus the essential circularity of pure self-awareness implies its self-causing nature, since that circularity is both a necessary and sufficient condition for its existence. By being aware of itself, pure self-awareness bootstraps itself into existence.

Hofstadter on the “strange loop” of self-awareness
The self-causing capacity of self-awareness has not just been noticed by philosophers with a metaphysical axe to grind. This capacity for self-causation, or at least the semblance thereof, has also been noted by the cognitive scientist Douglass Hofstadter, who focuses on self-referential structures (“strange loops”) as offering the key to the mystery of consciousness: “In the end, we are self-perceiving, self-inventing, [...] little miracles of self-reference.” (Hofstadter 2007: 363) Commenting on the “strange loop” of self-awareness, Hofstadter notes how this seemingly implies its self-causation: “It is almost as if this slippery phenomenon called “self-consciousness” lifted itself up by its own bootstraps, almost as if it made itself out of nothing.” (Idem: xii)

But note Hofstadter's reservation: “almost as if”. What gets in the way of Hofstadter’s full endorsement of the bootstrapping of self-consciousness is his adherence to physicalism, which forbids self-causation. As a physicalist, Hofstadter takes consciousness to be ultimately reducible to physical processes (the brain interacting with its environment). Hence his conclusion that the self-causing aspect of self-awareness must be an illusion, because physical processes (as they take place in time) cannot be self-causing. Thus he takes the self-causing aspect of self-awareness to be ultimately an illusion, a “mirage” (idem: 363), a surface appearance produced by myriad micro-feedback processes in the brain, processes that obey the standard laws of physics: “The problem is that in a sense, an “I” is something created out of nothing. And since making something out of nothing is never possible, the alleged something turns out to be an illusion, in the end, but a very powerful one.” (Idem: 292)

But here the Hard Problem of Consciousness comes to our rescue. The Hard Problem of Consciousness shows the irreducibility of consciousness to physical and computational structures. This means that the self-producing structure of self-awareness need not be illusory simply because it is ruled out by physics. We see, therefore, that the Hard Problem of Consciousness opens the possibility that the self-causation of self-awareness is genuine.

Two common mistakes about Absolute Idealism
There are, however, two common mistakes about Absolute Idealism which stand in the way of its proper understanding and evaluation – mistakes which we therefore have to correct. These common prejudices are (1) that Absolute Idealism was first and foremost a creature of the 19th century, originating with the post-Kantian German Idealists (Fichte, Schelling and Hegel) and then taken up and developed further by the Anglo-American Idealists (Green, Bradley, McTaggart, Royce); and (2) that Absolute Idealism was subsequently, at the beginning of the 20th century, refuted by the founding fathers of Analytic Philosophy, Moore and Russell in particular, as well as by empirical science, and has since then become obsolete.

The Sanskrit term "Upanishad" means "sitting down near"
and refers to the student sitting down near the teacher
in order to receive esoteric teaching

As regards the first prejudice, it is easily dispelled by even a cursory glance at the millennia-long history of Absolute Idealism in both Western and Eastern philosophy. This history arguably began in ancient India, notably in the Vedantic philosophy of the Upanishads (around the 7th century BCE). From there it migrated to the West, where it reached its first fully mature form in the Neoplatonism of Plotinus (3rd century CE – it is quite possible that Plotinus was influenced by the Vedanta; see Bréhier 1958). To a large extent the post-Kantian German Idealists merely rediscovered / reconstructed this new type of Idealism inaugurated in the West by Plotinus (cf. Beierwaltes 2004). Plotinus, then, was not just the originator of the notion of self-causation in Western philosophy; he was also the first Western philosopher to make the Absolute-Idealist identification of the self-causing cause of reality with self-awareness.

Bertrand Russell (1872-1970):
"It was towards the end of 1898 that
Moore and I rebelled against both
Kant and Hegel. Moore led the way,
but I followed closely in his footsteps."
(Bertrand Russell, My Philosophical
Development. London: Allen and
Unwin, 1959, p.42.)

Let us now turn to the second prejudice. Hasn’t Absolute Idealism been refuted by the founding fathers of Analytic Philosophy, Moore and Russell? And hasn’t it since then become obsolete? Well, histories of philosophy tend to present each new school of philosophy as arising by refutation of its predecessor, whereas the actual fact of the matter is often a lot more complicated. This holds no less for the “creation myth” of Analytic Philosophy, according to which the latter emerged by overthrowing the Absolute Idealism of the British Hegelians (who were the teachers of Moore and Russell). Recent historical scholarship has done much to discredit this triumphalist history. As Hylton notes in his Russell, Idealism, and the Emergence of Analytic Philosophy: “For every argument that Moore or Russell could mount against Idealism, there is an idealist reply which points out a distinction that is being neglected, or one that is drawn erroneously; an assumption smuggled in, or the sense of a term distorted.” (Hylton 1990: 105) In addition to this comes the fact that Absolute Idealism is currectly making something of triple comeback: two comebacks in Analytic Philosophy itself, and one comeback in contemporary physics. I will discuss these developments below.

The Normative Idealism of the Pittsburgh Hegelians
To begin with Analytic Philosophy, here we see Absolute Idealism return in both epistemology and the philosophy of mind. In epistemology we find the so called “Pittsburgh Hegelians” John McDowell and Robert Brandom, who have made a remarkable return to both Kant and Hegel by pointing out that conceptuality and rationality in general are intrinsically normative, having to do with how people ought to think rather than with how they factually think. On the basis of this “normativity of the conceptual” they argue for a Hegelian form of conceptual holism, such that – to paraphrase Hegel – the truth lies only in the conceptual whole that includes empirical reality (cf. Redding 2007). For given the conceptually laden impact of empirical experience on thought, the empirical world must have a normative significance that cannot be accounted for in strictly physicalist terms. According to McDowell and Brandom, therefore, the empirical world turns out to have a normative-conceptual structure that is best understood in terms of Hegel’s Absolute Idealism, where there is nothing outside of conceptual whole of “Absolute Knowledge”. I hope to be able to say more about Pittsburgh Hegelianism in later posts on this blog.

From the Hard Problem of Consciousness to Absolute Idealism
In the philosophy of mind, as we have already noted, we see the Hard Problem of Consciousness (HPC) give rise to serious doubts concerning the physicalist ontology adopted by earlier analytic philosophers. As a result, the philosophical landscape has changed dramatically, from a thoroughly physicalist one, where consciousness was accorded no independent status apart from the physical, to a much more ambiguous landscape with different competing philosophical positions stressing the ontological independence of consciousness – positions such as Property Dualism, Russellian Monism, Panpsychism, Micropsychism, and Idealist Monism.

In this context Absolute Idealism, too, is being reconsidered as perhaps the best response to the HPC (cf. Sprigge 1983; Hutto 2000; D'Oro 2005). The simple but crucial point here is that if consciousness is irreducible to physical reality (as the HPC shows), then mind-body interaction is only possible if the converse reduction holds, i.e. if physical reality reduces to consciousness. But this claim, that physical reality reduces to consciousness, amounts to Idealist Monism. Therefore: the HPC + mind-body interaction = Idealist Monism. And Idealist Monism is only a few steps away from Absolute Idealism.

The mystery of mind-
body interaction

Let us consider the above argument in some more detail. On the one hand, the HPC shows that consciousness cannot be explained in exclusively physical terms, such as brain activity. Thus the HPC refutes physicalism. But how, then, do consciousness and physical reality interact? There is no denying that such interaction takes place. Stimulate the brain and as a result consciousness changes. Conversely, a conscious exertion of the will usually results in limbs moving etc. How is this mind-body interaction possible if physicalism is false? The HPC leaves open only two possibilities: either consciousness and physical reality are two mutually independent realms of reality (Dualism) or physical reality is ultimately explainable in terms of (i.e. reduces to) consciousness alone (Idealist Monism). But, clearly, Dualism cannot account for mind-body interaction. For how could two utterly different and mutually independent realities possibly interact? (See e.g. the absurdity of Descartes' pineal gland.) Thus, since the HPC leaves open only these two possibilities, Dualism and Idealist Monism, the latter option must be true – that is: physical reality must ultimately reduce to consciousness, because consciousness can obviously interact with consciousness.

In other words: if we conceive of physical reality as a kind of manifestation of consciousness itself, then mind-body interaction becomes unproblematic. For then this interaction is ‘simply’ a case of consciousness interacting with one of its own manifestations, thus with itself in a sense. Of course, there really is nothing ‘simple’ about such Idealist Monism, since we still need an account of how consciousness produces the physical.

But Idealist Monism is not necessarily the same as Absolute Idealism. So how do we get from the former to the latter? Here the following consideration seems to be relevant. We already saw that the HPC saves the self-causation of self-awareness from the critique by physicalism. But the relation works the other way as well: the self-causation of self-awareness explains the HPC, i.e. it explains why consciousness is irreducible to physical reality. From the self-causation of self-awareness, after all, we have to conclude that self-awareness is the self-causing cause of reality as such – in other words: consciousness (in the form of self-awareness) is the basic ‘stuff’ of which reality consists, reality’s most primitive constituent. From this it obviously follows that consciousness is irreducible: it cannot be explained in terms of anything besides itself. Consciousness can only be explained in terms of consciousness, ultimately in terms of self-awareness.

Thus, when Chalmers (1995: 200) writes: “There is nothing that we know more intimately than conscious experience, but there is nothing that is harder to explain”, he thinks he is stating a paradox (“despite its intimacy, we can't explain consciousness”), whereas in fact he is stating the very explanation of consciousness’ irreducibility. For it is precisely the intimacy with which we know conscious experience (i.e. the self-evident experience of our own self-awareness, with its self-causing capacity) that explains why consciousness is reality’s most basic constituent.

John A. Wheeler (1911-2008)

The Absolute Idealism of Wheeler’s Self-Observing Universe
Beyond philosophy, moreover, we see Absolute Idealism return in contemporary physics (the paradigm of empirical science, at least for most analytic philosophers), notably in John A. Wheeler's theory of the Self-Observing Universe. Drawing on Idealist tendencies in both quantum mechanics (the observer dependency of wave function collapse) and digital physics (the constitutive importance of information for physical reality), the theoretical physicist Wheeler argued that the totality of physical reality – i.e. the universe – brings itself into existence by evolving those conscious subjects whose scientific observations and binary yes/no questions give “tangible reality” to the mathematical structure which is the universe. As Paul Davies summarizes: “Conventional science assumes a linear logical sequence: cosmos → life → mind. Wheeler suggested closing this chain into a loop: cosmos → life → mind → cosmos.” (Davies 2006: 281)

Wheeler's U diagram of
the Self-Observing Universe

For Wheeler, then, the universe is the self-creating Absolute, the Whole that brings itself into existence through mediated self-observation (mediated, namely, by the observers existing in the universe). In this way Wheeler resurrected the core idea of Absolute Idealism (the self-creation of Absolute Self-Awareness) within the context of contemporary physics. To be sure, Wheeler's theory of the Self-Observing Universe is so far nothing more than a hypothesis, or rather – as Wheeler himself stressed – an “idea for an idea”. It is by no means yet an empirically testable hypothesis, let alone a well-established scientific theory. Nevertheless, the fact that it presents a distinct scientific possibility, worthy of further investigation, is acknowledged by many physicists. (I discuss Wheeler’s hypothesis of the Self-Observing Universe in more detail here and here.) All in all, then, Absolute Idealism is still a live option, both in philosophy and science.

References
-Beierwaltes, Werner (2004), Platonismus und Idealismus. Frankfurt: Vittorio Klostermann.
-Bréhier, Émile (1958), The Philosophy of Plotinus. Chicago: The University of Chicago Press.
-Chalmers, David (1995), “Facing Up to the Problem of Consciousness,” in: Journal of Consciousness Studies 2(3): 200-19.
-(1996), The Conscious Mind: In Search of a Fundamental Theory. New York and Oxford: Oxford University Press.
-Davies, Paul (2006), The Goldilocks Enigma: Why is the Universe Just Right for Life? London: Penguin Books.
-D’Oro, Giuseppina (2005), “Idealism and the philosophy of mind,” in: Inquiry 48 (5): 395-412.
-Gerson, Lloyd (2011), "Goodness, Unity, and Creation in the Platonic Tradition", in: John F. Wippel (ed.), The Ultimate Why Question: Why Is There Anything at All Rather than Nothing Whatsoever?, pp. 29-42. Washington, D.C.: The Catholic University of America Press.
-Hofstadter, Douglas (2007), I Am a Strange Loop. New York: Basic Books.
-Hutto, Daniel D. (2000), Beyond Physicalism. Amsterdam: John Benjamins Publishing Company.
-Hylton, Peter (1990), Russell, Idealism, and the Emergence of Analytic Philosophy. Oxford: Oxford University Press.
-Plotinus, Enneads, translation by A.H. Armstrong, Loeb edition.
-Radhakrishnan, Sarvepalli (1953), The Principal Upanishads. New York: Harper.
-Redding, Paul (2007), Analytic Philosophy and the Return of Hegelian Thought. Cambridge: Cambridge University Press.
-Rosenblum, Bruce & Kuttner, Fred (2011), Quantum Enigma: Physics Encounters Consciousness. Oxford: Oxford University Press.
-Royce, Joshiah (1899 [1959]), The World and The Individual, First Series: The Four Historical Conceptions of Being. New York: Dover Publications.
-Schelling, F.W.J. (1800 [2001]), System of Transcendental Idealism. Translated by Peter Heath. Charlottesville: University Press of Virginia.
-Sprigge, Timothy L.S. (1983), The Vindication of Absolute Idealism. Edinburgh: Edinburgh University Press.