BBC Radio Discussion of the Philosophy of Berkeley

Philip Pilkington discusses a BBC radio program on George Berkeley here.

And the program is here:

Bishop Berkeley, BBC Radio 4, In our Time.

Links
Philip Pilkington, “BBC Radio Program on George Berkeley,” Fixing the Economists, March 20, 2014
http://fixingtheeconomists.wordpress.com/2014/03/20/bbc-radio-program-on-george-berkeley/

More Problems with Idealism

By “idealism” I refer to either

(1) George Berkeley’s (1685–1753) theistic subjective idealism (or immaterialism) that invokes a god of classical theism as the “greater mind” that creates both finite minds and the ideas given to minds, or

(2) a non-theistic idealism that is agnostic about what the “greater mind” actually is.

It is interesting that Berkeley’s idealism was clearly directed both against (1) the radical skeptics of his day and (2) the materialist atheists (Grayling 2005: 166–167).

For the empiricists of Berkeley’s era had opened up profound epistemological problems by stressing the differences between

(1) appearances (our conscious experiences and sensations), and

(2) reality (some posited external world).

In the terminology of Berkeley, there is thus a gap between (1) human “ideas” and (2) “things” (of the external world) (Grayling 2005: 168). Our internal sensations (or ideas) do not give us direct access to the external world, so how can we have knowledge of it? The latter was the question asked by radical skeptics.

Berkeley’s answer was to simply argue that the material “things” of the external world do exist (Grayling 2005: 168): only ideas and minds exist. Therefore we have direct experience of ideas – the only things that exist apart from minds.

Under Berkeley’s idealism, god is the external cause of finite human minds and the consistent and non-illusory ideas we have. For, given that there are many consistent ideas not under our control, Berkeley admits that the order seen in such consistent ideas must have some systematic cause: hence it is god (Mackie 1982: 71).

One of Berkeley’s maxims is the idea that “to exist is to be perceived” (or in Latin esse est percipi), and thus our existence and the ideas of our conscious life are causally dependent on god’s “perception.” Thus, for example, Berkeley accepts that the table in your kitchen still exists when nobody is in the room perceiving it, because it is still perceived by god.

By contrast, the non-theistic idealist does not necessarily need a god of classical theism, just a “super-mind” or “uber-consciousness” that is the cause of our finite human minds and our ideas. In what follows, I will refer to the non-theistic idealist’s greater mind as the “super-mind.”

I argue that these are crucial points in any debate with idealists:

(1) Epistemologically speaking, the idealist is in the same fundamental position as the indirect realist materialist: the idealist posits an external and directly unobserved cause of our given consistent ideas and perceptions. For neither (1) the external world of realism nor (2) the god or “super-mind” of idealism is directly observable or directly experienced in immediate conscious life.

Now I stress that this is not necessarily a problem for the idealist, but it is an important observation that means that in this respect the idealist position is not epistemologically superior to the realist one;

(2) Epistemologically speaking, the idealist – unless he can provide a valid and sound deductive argument or arguments – must use inductive arguments on the basis of indirect evidence to prove his hypothesis of a god or “super-mind.”

But that means, epistemologically speaking, that the idealist and the realist are also on the same ground, since the indirect realist’s belief in an external world is also an inductive inference on the basis of indirect evidence.

So again in this respect the idealist position is not epistemologically superior to the realist one, but on a par;

(3) Berkeley’s argument that “an idea can be like nothing but an idea” is unconvincing;

(4) Berkeley’s theistic god is a clear weak point in this theory, and it is not a simpler theory than realist materialism;

(5) on many issues, idealism of any type has weak explanatory power and often no explanatory power at all.

I think I have already explained (1) and (2) above, so let us proceed to (3), (4) and (5) below.

(3) An idea can be like nothing but an idea?
Berkeley makes this argument in The Principles of Human Knowledge, section 8.

J. L. Mackie shows why the indirect realist position is not refuted by Berkeley:

“… that an idea can be like nothing but an idea, collapses when we see what sort of likeness or resemblance the materialist view requires. This is just, for example, that when I am in a perceptual state whose content is describable by saying that I seem to be seeing something square, there should be something that is (approximately) square. Or again, that when it is with me as if I were seeing two objects of similar shape and size, say two billiard balls, there should really be two similarly shaped and sized objects in the neighbourhood. The likeness or resemblance required is just that where the content is as of an X, the reality should be (roughly) an X. There simply is no a priori impossibility or even implausibility about something other than an idea being like an idea in this sense.” (Mackie 1982: 72).

Perfect or exact resemblance between our sensory states and objects of the real world is unnecessary for the indirect realist position.

All we need is (1) an approximate similarity and/or (2) a relationship of causal dependence from objects in the external world running to some of our sensations, which does not exclude that, in a modern scientific sense, the object of the external world that is the causal origin of some perception has many properties not observable to us.

(4) Berkeley’s theism is fraught with difficulty
Berkeley’s idealism is based on a theistic conception of human minds: that humans are created by a god, and (presumably) fundamentally different from animals.

First, a problem here is: do animals have minds? How does the idealist offer an answer to this question? It is not clear what Berkeley thought (Cummins 2005: 190).

Secondly, as we have seen, for Berkeley god is the external cause of the regularity in many of our ideas.

So Berkeley needs to prove the existence of god. But the history of attempts to use deductive arguments for the existence of god is one of utter failure (and I rely on Michael Martin’s [1990] survey and critique here), so Berkeley’s argument must fall back on inductive arguments.

The problems with Berkeley’s actual argument for god are well known (Mackie 1982: 64–80). For one thing, the cause of the consistency of the ideas beyond our control might not be unitary. Why can’t it be explained by many “super-minds” or panpsychism? (Mackie 1982: 71).

Even if we put all those difficulties aside, there is still a severe problem: the hypothesis of a theistic god is much more complex and more extravagant than a realist materialist hypothesis.

Berkeley, of course, argued that his idealist hypothesis with a god was the simpler explanation invoking Occam’s razor. But this contention is unconvincing.

Consider the attributes of the god of classical Judeo-Christian theism, with additional ones required by Berkeley:

(1) god is a personal and conscious mind;

(2) god is omnipotent;

(3) god is omniscient;

(4) god is perfectly good;

(5) god constantly maintains the existence of finite minds and their ideas in a process we can’t understand but which appears miraculous.

I submit to you that these attributes make the god invoked by Berkeley an extremely complex entity, possibly the most complex thing you could postulate.

In fact, there is still debate about whether properties like omnipotence, omniscience, and perfect goodness in one being can even be logically possible (Martin 1990: 278–316).

By contrast, look at the attributes of a real physical universe as postulated by science:

(1) the external universe of matter and energy is not conscious nor it is a personal entity, and in this respect is a simpler entity than a theistic god;

(2) following from (1) the universe is not omnipotent, omniscient, nor perfectly good, and in this respect is a simpler entity than a theistic god;

(3) the universe consists of matter and energy and its relations governed by a limited set of regularities we call “physical laws,” which can be discovered by humans through inductive and experimental science. Thus the external universe is a simpler entity than the miraculous powers of a theistic god.

(4) all complex things in the universe like life and minds have been built up and created over many billions of years by relatively simple and well understood processes like Darwinian evolution by natural selection. The existence of minds does not require some inexplicable miracle, but is explicable under a realist materialist view.

One can add that the realist materialist view also explains evil and suffering in a far better way than theistic idealism, amongst its many merits.

In short, the realist materialist position is the simpler and better explanation – and, under the principle of Occam’s razor, the preferable one.

Furthermore, even Berkeley’s master argument, if it is really taken to be a devastating argument against the existence of a real external world of objects, would apply to other minds and to the “super-mind”:

“Secondly, if the [sc. Master] argument were sound, it would prove too much. Although … [sc. Berkeley] states it with regard to sensible objects like houses and books, their nature as sensible objects plays no part in the argument; so, if it held at all, it would hold equally against the suggestion that I can conceive that there are minds that are not conceived by me; thus it would establish solipsism, in which I would reject as not even conceivable the existence not only of material things but also of other minds and spirits, including God, except in so far as they are conceived by me. This line of argument is, therefore, not only fallacious but also, in these two ways, misdirected.” (Mackie 1982: 68).

That is, think of a mind that you do not perceive now. There is a vast amount of empirical evidence that other minds exist even though you do not perceive them.

But if we cannot conceive of a mind without it being perceived, it follows that in any initial thinking through idealist philosophy, you have no good reason to think any minds exist that you do not immediately perceive. But, says Berkeley, god perceives them, so they do exist. But Berkeley’s argument works just as well against god or the “super-mind”!

If we have no direct perception of the “super-mind,” who perceives the “super-mind” and causes its existence? And who perceives the “super-super-mind,” and so on?

That is, Berkeley’s philosophy must cut off an infinite chain of explanation by positing “god” or the “super-mind” as a “brute fact” that is inexplicable. But, in that respect at least, it is no better than a materialist viewpoint that posits the universe as the ultimate “brute fact,” the difference being, as we have seen, that the hypothesis of a real universe is simpler and by Occam’s razor a better hypothesis.

(5) Realist Science has great explanatory power and Idealism does not
Our natural sciences have produced a vast set of theories that explain the world we experience, and under the indirect realist interpretation we can posit an external world of real objects of matter and energy affected by forces.

As just a sample, consider the following theories:

(1) the Big Bang theory;

(2) the theory of the development of gases, stars, planets and galaxies;

(3) the theory of the origin of life by biochemical processes;

(4) the theory of Darwinian natural selection acting on self-replicating biochemical compounds and living things, producing a great diversity of life over many billions of year on earth;

(5) the theory that human beings evolved from lower life-forms and that various types of minds too evolved gradually and incrementally as a product of evolution.

If one takes an idealist view, whether Berkeley’s or a non-theistic idealism, none of these theories can be literally true, for there is no external word of matter and energy.

Minds were created by god or the “super-mind” and did not arise by gradual material processes.

But we have a vast amount of empirical evidence available to our senses that can be used in inductive argument to support the truth of these theories.

Our realist materialist science has a strong explanatory power explaining the wealth of data we see, but idealist philosophy – whether of Berkeley or a non-theistic idealism – has weak explanatory power and often no explanatory power at all.

This point is very easy to prove, I think.

We need only think of fossils. Our conscious life presents to us things we call fossils, and by inductive inference we infer that they are the remains of living things long dead. A realistic materialist science explains what fossils are, and indeed can use them to reconstruct a history of life on earth: things that really existed in an external world, including a specific long line of animal life forms from which human beings are descended.

But what explanation can an idealist offer for fossils? As we have seen the idealist faces difficulties answering the question whether higher animals even have minds. If animals do not have minds, then they must be mere “ideas” given to the mind by god or the super-mind. I feel certain that no idealist would content that plants have minds, so how does the idealist explain plant fossils?

What explanation can the idealist give under his theory, except to say it is another mystery?

And why has god or the super-mind given us a wealth of sensory ideas that lead us to inductively infer that our “world” once had living animals and plants now dead? Is god or the super-mind engaged in deception and fraud? If so, why?

Or take another example: why is it that some people have different perceptions of colour? (e.g., colour blindness). Why does god or the super-mind that create minds with different types of colour perception?

A realist materialist gives us a clear explanation: colour blindness is either (1) genetic and a problem with genes or (2) caused by certain diseases.

Again and again, I contend we can find endless puzzling problems from our conscious life that realist materialist science gives a powerful explanation of, but which cannot be adequately explained by idealism.

Update
Philip Pilkington has a response to me on idealism here:

Philip Pilkington, “The Mystery of Matter: A Response to Lord Keynes on Berkeley’s Idealism,” Fixing the Economists, February 27, 2014.
http://fixingtheeconomists.wordpress.com/2014/02/27/the-mystery-of-matter-a-response-to-lord-keynes-on-berkeleys-idealism/

BIBLIOGRAPHY
Cummins, Phillip D. 2005. “Berkeley on Minds and Agency,” in Kenneth P. Winkler (ed.), The Cambridge Companion to Berkeley. Cambridge University Press, Cambridge and New York. 190–229.

Dicker, Georges. 2011. Berkeley’s Idealism: A Critical Examination. Oxford University Press, Oxford and New York.

Grayling, A. C. 2005. “Berkeley’s Argument for Immaterialism,” in Kenneth P. Winkler (ed.), The Cambridge Companion to Berkeley. Cambridge University Press, Cambridge and New York. 166–189.

Mackie, John Leslie. 1982. The Miracle of Theism: Arguments for and against the Existence of God. Clarendon Press, Oxford.

Martin, Michael. 1990. Atheism: A Philosophical Justification. Temple University Press, Philadelphia.

Berkeley’s Idealism: A Critique

I enjoy a good debate in philosophy. Philip Pilkington puts up a strong defence of idealism in the comments of the last post, and I’m interested enough in idealism to examine in greater detail why I don’t think it is convincing.

George Berkeley’s (1685–1753) philosophy of subjective idealism (which he called “immaterialism”) has two bold and fundamental assertions about reality:

Proposition (1): that the only things that exist are (i) minds and (ii) objects of perception (ideas), and

Proposition (2): the objects of perception only exist at the same time when they are perceived by a mind (Stoneham 2009: 119).

It follows from this that the external world of matter we normally think exists does not exist, under Berkeley’s ontology.

I think any non-dogmatic realist would accept that it is possible that these propositions might be true. Also, I doubt whether any idealist can prove such propositions with necessary or apodictic truth. Also, I assume that a non-dogmatic idealist would also admit that it is possible that the realist position might be true.

Realists and materialists who reject Berkeley’s idealism come in two main groups:

(1) indirect or representative realists (and modern scientific realists), and

(2) direct realists. (Stoneham 2009: 120–121).

Direct realists would argue that actual physical objects in the external world are amongst the “objects of perception,” whereas the indirect realists argue that physical objects in the external world are not amongst Berkeley’s “objects of perception.”

Thus it is possible for an indirect realist to accept Berkeley’s proposition (2) above, but reject as untrue proposition (1) above.

On realism, I take position (1): the indirect or representative realist view. This states that it is highly probable that there is an external physical world of objects or things/events that corresponds indirectly to some objects of perception in the sense that some objects of perception are causally dependent on real objects.

But we do not have direct access to the external objects of reality, but only to some conscious “objects of perception” that are causally dependent on them. That is to say, the objects and events of the world of matter and energy described by science are not objects of immediate experience/“objects of perception”.

So the indirect realist/materialist’s inductive argument does not say that the external object and the internal “objects of perception” are absolutely equivalent (as noted in Stoneham 2009: 121).

The human mind’s “objects of perception” are representations (with colour sensations, shapes and so on) of sense data from the external world such as, for example, from the swarm of particles called a tree, and this system of internal representation is the product of Darwinian evolution, and one could conceive of a mind capable of representing the same tree in different ways from different data beyond the visible spectrum (e.g., infrared or x-rays).

Furthermore, the actual qualities we perceive in our minds like green and red are not qualities of the actual object existing in material reality, but are merely causally dependent on them to some extent (e.g., light waves reflected off the object are the causal factor for perception of colours).

So we see that the indirect realist makes a crucial distinction between (1) “objects of perception” and (2) external objects that we do not experience directly. Our argument for the existence of an external world of events/objects is an inductive one based on empirical evidence. Its truth is at most very probable, not certain.

But to return to Berkeley’s arguments, as Stoneham (2009: 121) notes, Berkeley has a great many arguments for his two fundamental positions, such as

(1) the argument that there is no serious difference between primary qualities (such as size, motion and shape) and secondary qualities (colour, taste and texture), against Locke’s claim that primary qualities inhere in the external objects we perceive, and

(2) the so-called “master argument”;

These major arguments are presented in The Principles of Human Knowledge (1710) and Three Dialogues between Hylas and Philonous (1713).

I intend below to focus on what has come to be called Berkeley’s “master argument” (coined by Gallois 1974) because Berkeley intended it to be a crucial argument in support of his idealism.

I. The Master Argument
First, let us look at the master argument as written in The Principles of Human Knowledge (1710):

“22. …. Insomuch that I am content to put the whole upon this issue – if you can but conceive it possible for one extended moveable substance, or, in general, for any one idea, or anything like an idea, to exist otherwise than in a mind perceiving it, I shall readily give up the cause. And, as for all that compages of external bodies you contend for, I shall grant you its existence, though you cannot either give me any reason why you believe it exists, or assign any use to it when it is supposed to exist I say, the bare possibility of your opinions being true shall pass for an argument that it is so.

23. But, say you, surely there is nothing easier than for me to imagine trees, for instance, in a park, or books existing in a closet, and nobody by to perceive them. I answer, you may so, there is no difficulty in it; but what is all this, I beseech you, more than framing in your mind certain ideas which you call books and trees, and at the same time omitting to frame the idea of any one that may perceive them? But do not you yourself perceive or think of them all the while? This therefore is nothing to the purpose it only shews you have the power of imagining or forming ideas in your mind; but it does not shew that you can conceive it possible the objects of your thought may exist without the mind. To make out this, it is necessary that you conceive them existing unconceived or unthought of, which is a manifest repugnancy. When we do our utmost to conceive the existence of external bodies, we are all the while only contemplating our own ideas. But the mind, taking no notice of itself, is deluded to think it can and does conceive bodies existing unthought of or without the mind, though at the same time they are apprehended by or exist in itself. A little attention will discover to any one the truth and evidence of what is here said, and make it unnecessary to insist on any other proofs against the existence of material substance.” (The Principles of Human Knowledge §21–22).

Next, the master argument in Three Dialogues between Hylas and Philonous (1713). In this philosophical dialogue, Philonous is Berkeley’s mouthpiece:

“Philonous: Either, Hylas, you are jesting, or have a very bad memory. Though indeed we went through all the qualities by name one after another, yet my arguments or rather your concessions, nowhere tended to prove that the Secondary Qualities did not subsist each alone by itself; but, that they were not at all without the mind. Indeed, in treating of figure and motion we concluded they could not exist without the mind, because it was impossible even in thought to separate them from all secondary qualities, so as to conceive them existing by themselves. But then this was not the only argument made use of upon that occasion. But (to pass by all that hath been hitherto said, and reckon it for nothing, if you will have it so) I am content to put the whole upon this issue. If you can conceive it possible for any mixture or combination of qualities, or any sensible object whatever, to exist without the mind, then I will grant it actually to be so.

Hylas: If it comes to that the point will soon be decided. What more easy than to conceive a tree or house existing by itself, independent of, and unperceived by, any mind whatsoever? I do at this present time conceive them existing after that manner.

Philonous: How say you, Hylas, can you see a thing which is at the same time unseen?

Hylas: No, that were a contradiction.

Philonous: Is it not as great a contradiction to talk of conceiving a thing which is unconceived?

Hylas: It is.

Philonous: The tree or house therefore which you think of is conceived by you?

Hylas: How should it be otherwise?

Philonous: And what is conceived is surely in the mind?

Hylas: Without question, that which is conceived is in the mind.

Philonous: How then came you to say, you conceived a house or tree existing independent and out of all minds whatsoever?” (Three Dialogues between Hylas and Philonous, first dialogue).

It seems clear that Berkeley thinks of “sensible objects” or “ideas” as the objects of perception (Stoneham 2009: 119).

Now since both passages above present an informal argument, let us re-write it as the following mixed conditional syllogism:

Major premise: If conscious ideas/sensations cannot even be conceived without a mind, then conscious ideas/sensations cannot exist externally or independently of a mind.

Minor premise: Conscious ideas/sensations cannot even be conceived without a mind

Conclusion: Therefore conscious ideas/sensations cannot exist externally or independently of a mind.

This argument is formally valid. Let us assume that its major premise is sound, to make it easy for the idealist.

It follows that the conclusion is necessarily true.

What does this prove? It certainly does not prove that an external world of matter, containing objects on which some of our ideas/sensations/perceptions are causally dependent, does not exist.

As Stoneham (2009: 121) argues, it is only evidence in support of Berkeley’s proposition (2) above. That is, it proves only that conscious sensations or ideas of any type cannot exist independently of minds. But this is not denied by modern indirect realist materialists/physicalists.

In short, the “master argument” is no devastating demolition of the indirect realist arguments for the reality of an external world of matter and energy as described by science: it is consistent with it.

If Berkeley has some definitive argument against the existence of an external world of matter, the master argument does not qualify for such an argument.

Let us now turn to some other criticisms of both Berkeley’s idealism and the non-theist versions.

II. The Consistency of Conscious Experience
There is a high degree of consistency in the passive sense data or certain “objects of perception” that we cannot control, both between different people and in the same mind over time.

Berkeley does not deny this. Berkeley admits that some ideas of sensation and perception (as opposed to dreams or imagination) are given to the mind and not freely determined by the conscious mind (Musgrave 1993: 127). Regularities in our experience are “laws of nature” for Berkeley (Musgrave 1993: 128).

It would appear that the consistency requires an explanation. In fact, Berkeley did invoke a common cause and an external cause (external to the mind of the individual) to account for it: a theistic god. His explanation is that a theistic god of the type familiar from Judeo-Christian theology is the cause of the consistency of our sensory experiences, and he must be a benevolent one for he does not engage in pernicious and confusing changes in our normally consistent “objects of perception.”

But that raises a whole set of assumptions and the need for a rock-solid argument for the existence of god, something which, as modern philosophy has shown, is a highly problematic exercise.

But what about the non-theistic idealist? The observation about consistency becomes a “brute fact” for the non-theistic idealist. He cannot really explain it, and this leads me into my third criticism.

III. Non-Theistic Idealism has weak Explanatory Power
A final argument against non-theistic idealism is that it is utterly incapable of providing any answers to fundamental question about existence:

(1) why do we have a conscious existence with a high degree of consistency and what looks like external constraints facing us?;

(2) where do minds come from?;

(3) in fact, how can you justify the view that other minds even exist? (why doesn’t non-theistic idealism collapse into solipsism?);

(4) if the idealist accepts that other minds exist, do animals have minds?

One could add a welter of other questions to these, but the conclusion is clear: the explanatory power of idealism is feeble and weak (Musgrave 1988: 241), and the idealist must shrug his or her shoulders and proclaim that we cannot even begin to seriously answer these questions.

By contrast, the indirect realist materialist can provide convincing answers to all these questions from our best scientific theories and inductive argument.

For example, take point (3): the charge that non-theistic idealism leads to solipsism. If the only direct experience you have of conscious minds is inside your own conscious mind and one does not believe in the existence of an external world of matter, then what reason is there to think that any other minds even exist?

For the materialist, one strong and straightforward argument is that we have a strong degree of empirical evidence that human minds are causally dependent on brains, and empirical investigations of other human beings show that they have brains (either by non-invasive scanning technologies or sometimes surgery on living humans or autopsies on dead ones). It is therefore a convincing inductive inference that other human minds exist.

In short, here as in numerous other questions, an indirect realist materialism provides a theory with a rich and powerful explanatory power, which is lacking in idealism.

Further Reading
For a defence of idealism and a somewhat different interpretation of the master argument, see Philip Pilkington’s posts here:

Philip Pilkington, “Berkeley’s ‘Master Argument’ Doesn’t Exist,” Fixing the Economists, January 3, 2014.
http://fixingtheeconomists.wordpress.com/2014/01/03/berkeleys-master-argument-doesnt-exist/

Philip Pilkington, “Faith-Based Arguments in Empirical, Causal and Probabilistic Reasoning,” Fixing the Economists, October 4, 2013.
http://fixingtheeconomists.wordpress.com/2013/10/04/faith-based-arguments-in-empirical-causal-and-probabilistic-reasoning/

Philip Pilkington, “The Theory of Relativity: Anticipated at the Turn of the Seventeenth Century by George Berkeley,” Fixing the Economists, October 5, 2013.
http://fixingtheeconomists.wordpress.com/2013/10/05/the-theory-of-relativity-anticipated-at-the-turn-of-the-seventeenth-century-by-george-berkeley/

Philip Pilkington, “Berkeley’s ‘Master Argument’ Doesn’t Exist,” Fixing the Economists, January 3, 2014
http://fixingtheeconomists.wordpress.com/2014/01/03/berkeleys-master-argument-doesnt-exist/


BIBLIOGRAPHY
Freeley, and Austin and David Steinberg. 2014. Argumentation and Debate: Critical Thinking for Reasoned Decision Making (13th edn.). Wadsworth Cengage Learning, Boston, MA.

Gallois, A. 1974. “Berkeley’s Master Argument,” Philosophical Review 83: 55–69.

Grayling, A. C. 2005. “Berkeley’s Argument for Immaterialism,” in Kenneth P. Winkler (ed.), The Cambridge Companion to Berkeley. Cambridge University Press, Cambridge and New York. 166–189.

Mandik, Pete. 2014. This is Philosophy of Mind: An Introduction. Wiley Blackwell, Chichester.

Musgrave, Alan. 1988. “The Ultimate Argument for Scientific Realism,” in R. Nola (ed.), Relativism and Realism in Science. Kluwer Academic Press, Dordrecht. 229–252.

Musgrave, Alan. 1993. Common Sense, Science and Scepticism: A Historical Introduction to the Theory of Knowledge. Cambridge University Press, Cambridge and New York.

Rickless, Samuel Charles. 2013. Berkeley’s Argument for Idealism. Oxford University Press, Oxford.

Robinson, Howard. 2003. “Berkeley,” in Nicholas Bunnin and E. P. Tsui-James (eds.), The Blackwell Companion to Philosophy (2nd edn.). Blackwell, Malden, Mass. and Oxford, UK. 694–708.

Stoneham, Tom. 2009. “Berkeley. Arguments for Idealism,” in Robin Le Poidevin, Peter Simons, Andrew McGonigal, Ross Cameron (eds.), The Routledge Companion to Metaphysics. Routledge, London and New York. 119–130.