Is Berkeley justified in denying the existence of a material world?
Berkeley develops his immaterialist view in direct opposition to materialists. We must, however, explicate what Berkeley means by this: Materialism here means any view affirming the existence of material things. Material things on this account are mind-independent things, which exist without being perceived. Berkeley’s position is one, in which all things are held to be mind-dependent:
[…] what are […] objects but the things we perceive by sense, and what do we perceive besides our own ideas or sensations; and is it not plainly repugnant that any one of these [objects] or any combination of them should exist unperceived? (PHK4)
Indeed the famous dictum ‘esse is percipi’ (PHK3) is an accurate representation of the view that Berkeley expounds. In this essay we will examine several arguments that Berkeley levels against the existence of a mind-independent world and two of the most obvious replies to his idealism.
Material objects as represented
All ideas have their origin in perceptions, yet this does not entail that the perceptions themselves are causally related to an external material world.
By sight I have the ideas of light and colours with their several degrees and variations. By touch I perceive, for example, hard and soft, heat and cold, motion and resistance, and of all these more and less either as to quantity or degree. (PHK1)
Berkeley rejects the causal picture in favour of speaking with the ‘vulgar’: He proposes that what is immediately perceived is all there is. Accordingly no matter is needed to explain the existence of ideas in the mind.
A more sophisticated version of materialism, however, accounts for the difference between immediate ideas of the mind and mediately perceived qualities of matter (cf. Locke). On this view ideas resemble their object and are thought to be but copies of mind-independent qualities. This distinction nevertheless fails to evade Berkeley’s immaterialism:
But say you, though the ideas themselves do not exist without the mind, yet there may be things like them whereof they are copies or resemblances, which things exist without the mind, in an unthinking substance. I answer, an idea can be like nothing but an idea; a colour or figure can be like nothing but another colour or figure. (PHK 8)
As all that is perceived by the mind are ideas the notion that ‘an idea can be like nothing but an idea’ has devastating consequences to the materialist argument: All that exists within the mind are ideas, physical objects must be mediated by the senses so as to generate an idea in the mind. It is clear then that anything that could possibly be compared is one idea with another; no idea can be compared with a physical object. Hence no relation of resemblance between material things and ideas can subsist. The materialist has massive problems at this point how to characterise material things. Are they still said to be extension, shape and sound, then one might reply that such qualities are qualities of ideas. Consequently material objects cannot be like this.
Material objects as explanation
Materialism might still be maintained, since it retains its explanatory value. Where, if not from material objects do our ideas originate? Commonsense seems to dictate that the table and the pen correspond to actually existing physical objects causing our ideas of them. Regardless of this Berkeley continues:
[…] though we give the Materialists their external Bodies, they by their own confession are never the nearer knowing how our Ideas are produced: Since they own themselves unable to comprehend in what manner Body can act upon Spirit, or how it is possible it should imprint any Idea in the Mind. (PHK19)
He then goes on to offer an example of this explanatory disability:
Suppose […] an Intelligence, without the help of external Bodies, to be affected with the same train of Sensations or Ideas that you are, imprinted in the same order and with like vividness in his Mind. I ask whether that Intelligence hath not all the Reason to believe the Existence of corporeal Substances, represented by his Ideas, and exciting them in his Mind, that you can possibly have for believing the same thing? (PHK20)
Berkeley supposes that materialists themselves must doubt their own view, since sense affections are often found to be misleading (cf. Descartes). The materialist must thus admit to the fact that there do not have to be material objects corresponding to ideas. Furthermore Berkeley can invoke a problem set up by Dualism: If Mind and Body are distinct substances then how can one affect the other? The relation between ideas and material objects is then neither one of causality nor one of representation and the materialists cannot offer an alternative account of this relation. Furthermore, since the relation itself is only posited as an inference to the best explanation and this relation cannot be explained the inference should not be made.
Now that we have seen that the arguments Berkeley brings forward against the ‘materialists’ hold, we must consider what charges the ‘materialists’ may level against Berkeley and whether or not he can offer responses.
Real and imaginary things
Firstly, the materialist will object that to make all objects mind-dependent commits us to saying that there is no difference between real and imaginary objects. Both are after all ideas within a mind and have no substantial being beyond it. Berkeley’s response is as follows:
The Ideas of Sense are more strong, lively, and distinct than those of the Imagination; they have likewise a Steddiness, Order, and Coherence, and are not excited at random, as those which are the effects of Humane Wills often are […]. (PHK30)
Real things are discernible from imaginary ones by them not being voluntary; they are not the product of the will. This first distinction excludes all deliberate falsification of this distinction. However, it does not suffice, for it allows for hallucinations and dreams to remain ‘real’. The second criterion Berkeley introduces is designed to counter such a fallacy: Real things are real only in so far as they exhibit a ‘steddiniess, order, and coherence’; the real world is then constituted by its regularity and correspondence to a set of patterns.
Though we can now distinguish between what is real and what is imaginary, a major problem remains at hand: if to be is to be perceived then what can be said about things unperceived? Do they flash out of existence as they flash out of perception? Do they have a ‘steddiness’ of their own?
The existence of unperceived objects
Let us for a moment assume all the consequences of this: if I leave the room, the things in it cease to exist as they are not perceived. However, as I re-enter the things in the room will come back into existence. Berkeley himself seems confident that this objection does not pose too great a danger:
The Table I write on, I say, exists, that is, I see and feel it; and if I were out of my Study I should say it existed, meaning thereby that if I was in my Study I might perceive it, or that some other Spirit actually does perceive it. (PHK3)
Berkeley thinks that the things in my room will always be perceived when the right circumstances pertain. This argument depends, however, on one’s conception of God, for Berkeley God, as another external mind, guarantees the ‘steddiness’ of patterns, the right circumstances, so that any time I would re-enter the room I would find whatever things were there before. God as omnipresent being then offers stability and compliance to commonsense to Berkeley’s theory. 
Nonetheless Berkeley is hard-pressed to offer an alternative for those who ascribe God a different ontological status (e.g. non-existence): Certainly, Berkeley has the option of dismissing the argument concerning the existence of the table whenever it is unperceived, for it would be in line with speaking with the ‘vulgar’. What does it matter after all, if things cease to exist when unperceived, as long as they return into being as soon as they are perceived?
Berkeley’s idealist account offers us an interesting alternative to the standard materialist view: The mind-dependency of objects resolves issues that materialist philosophers had struggled with greatly and shows the arbitrariness of inferring the material world. However, Berkeley’s account cannot provide us with compliance to commonsense – something he thought would distinguish his view from the materialist doctrine. Indeed, whether one accepts his inference depends on what status one affords to unperceived objects, and as we have seen it is here that Berkeley fails to provide answers that resolve the issue without resort to an external guarantee. Whether or not to accept the claim that there is no material world then depends on one’s willingness to ‘bite this bullet’.
Berkeley, G. (1710). Of the Principles of Human Knowledge, Part I. Available at http://www.maths.tcd.ie/~dwilkins/Berkeley/HumanKnowledge/1734/HumKno.html [Accessed 4 May 2012]
Berman, D. (2004). George Berkeley. In Brown, S. ed. British Philosophy and the Age of Enlightenment. London: Routledge, pp. 101-122
Downing, L. George Berkeley. In Zalte, E.N. ed. The Stanford Encyclopedia of Philosophy (Spring 2011 Edition). Available at http://plato.stanford.edu/archives/spr2011/entries/berkeley/ [Accessed 4 May 2012]
McCracken, C. (2002). George Berkeley. In Nadler, S. ed. A Companion to Early Modern Philosophy. Oxford: Blackwell Publishers, pp. 437-455
Stoneham, T. (2005). George Berkeley: A Treatise Concerning the Principles of Human Knowledge. In Shand, J. Central Works of Philosophy 2: The Seventeenth and Eighteenth Centuries. Chesham: Acumen
 The term ‘materialism’ in contemporary philosophy is widely used to designate the view that all things, which exist are material.
 Berman, 2oo4, p.107
 Downing, 2011
 Downing, 2011
 McCracken, 2002, p. 444