How Berkeley Argues for Metaphysical Idealism

1. What is "metaphysical idealism"?

"Metaphysical idealism" is the name philosophers give to the theory of reality or "metaphysics" which holds that the only independently real entities or "substances" are minds and their properties. The most general catch-all word with which to refer to mental properties is "ideas." Thus "ideas" by definition are what "minds" have, they can exist only in minds or "spirits." They are what the mind is thinking of when it thinks. Idealists in effect accept the reality of only one half of Cartesian dualism, the "mind" or "thinking thing" half.

2. Does this mean that metaphysical idealists hold that there is no physical world?

No, Berkeley goes to great pains to insist that he is not denying the reality of anything which the person of common sense (the "vulgar") believes in. The only thing he does deny to be real, namely "matter" or "material substance," is, he argues, a philosophical abstraction which only "philosophers" (who do doubt the reality of the world we actually perceive) believe in. Materialists and dualists who do hold that matter or material substance is real and is the cause of our perceptions of physical objects are the ones who deny the common sensical belief that what is real is what we perceive. They hold instead the mechanistic world view, which denies that the world is as we perceive it, and insists that the physical world is composed of entities possessing only the primary properties of extension. All of the "secondary" properties we perceive physical objects as having, in reality exist only in our perceptions, not in the objects themselves. Berkeley is out to show that this view is absurd, inconsistent, confused, and leads to skepticism, and even worse, to atheism.

3. What does Berkeley think that physical objects are if they are not material substances in space and time?

Berkeley claims to prove that the physical objects, what he calls the "sensible objects," which we perceive can be only perceptions. His argument is extremely simple:

Premiss 1: Sensible objects are the things we perceive.
Premiss 2: What we immediately perceive are our perceptions.
Conclusion: Therefore, sensible objects are perceptions.

The argument appears to be valid, but its conclusion must be true only if the premises are true. The first premise of this argument is true by the definition of "sensible objects." It is the second premise, however, which seems startling. Most people would say that what they perceive are the objects themselves as they exist in space or the world "external" to the mind. However, Berkeley aims to show that this is a confusion.

4. Why does Berkeley think the second premise must be true?

The second premise, "What we immediately perceive are our perceptions" is itself the conclusion of two other arguments which concern most of the "First Dialogue." The first presented is the "Pain Argument, and the second is the "Argument from the Relativity of Perceptions."

5. What is the "Pain Argument"?

The "Pain Argument" reasons in the following way: It is granted that extreme degrees of many sensations are perceived immediately as painful. Notice we do not perceive, as it were, two sensations, for example an extreme degree of heat and a pain; we perceive only the extreme degree of heat which is the pain. However, only perceivers can experience pains. Therefore what the perceiver experiences in perceiving an extreme degree of certain sensations must exist only in the perceiver. Thus against what the materialist believes, the extreme degree of heat, for example, cannot exist in a material substance which is not a perceiver, but must exist only in the perceiver. But everything that exists in the perceiver, i.e. a "mind" or, in Berkeley's words, a "spirit," is, by definition, a "perception" or an "idea." A similar argument can be constructed on the basis of the fact that moderate degrees of many sensations are pleasures.

6. What is the "Argument from the Relativity of Perceptions"?

Berkeley considers examples in which the "same" object may appear to be the source of different incompatible sensations. The room temperature bowl of water will feel cool to the preheated hand and warm to the prechilled hand. But one and the same object cannot be both warm and cool, therefore what is perceived, the warmth in one case and the coolness in the other, cannot exist in the water, but must exist in the perceiver. In other cases where we alter the perceiver, the perception will alter, although it is believed that the alleged material substance existing outside the perceiver has not changed. Thus what the perceiver perceives cannot be something existing "outside" of the mind or spirit which does the perceiving, it must be "in the perceiver." But what are in the perceiver are all perceptions or ideas.

7. How did the mechanistic world-view explain the relativity of perception?

Defenders of materialism concluded that the world was not as we perceive it and admitted that most of what we perceive exists in the perceiver; these are the so-called "secondary properties" or "secondary qualities" which were not held to belong to the "material substance" existing in the "external" world, but exist only in our perception of them, i. .e in our mind.. Indeed, the claim that secondary properties exist only in the perceiver was defended by precisely the same argument for the relativity of perceptions that Berkeley uses. But the materialists held that this was true only of the secondary properties. The primary properties were alleged to exist in the material substance, as well as, of course, in our perception of the material substance. What Berkeley does is show that just like the so-called secondary properties, the so-called primary properties are also relative to the perceiver. Thus if the materialists argue that being relative to the perceiver was a good reason to believe that the secondary properties exist only in the perceiver, it is equally well a good reason for believing that the so-called primary properties exist only in the perceiver. In other words, Berkeley's argument shows that as far as perception is concerned, there's really no difference between so-called "primary" and so-called "secondary" properties; they both exist only in the perceiver, and since everything that exists in a perceiver (a "mind" or "spirit") is a perception (or an "idea") both primary and secondary properties are therefore nothing but perceptions in minds. Part of the genius of Berkeley's argument from the relativity of perceptions is that he uses the very same argument that materialists used, but he extends it further.

8. But don't we perceive material substances?

No, not by the definition of "material substance" or "matter" that materialist philosophers defended. What they meant by these terms was supposed to be something that had the primary properties of extension, not the properties themselves; the substance is imagined to "underlie" or "support" its properties and so was called a "substratum." What we perceive, of course, are the properties of the substance, but not the substance having the properties. Thus if the substance is stripped from having its primary as well as its secondary properties, there's nothing left in the substance to perceive.

9. Even if we do not perceive material substance, could we not infer by cause and effect reasoning that there must be some sort of substance "out there" in space causing the perceiver to have the perceptions of primary and secondary properties?

Berkeley insists the answer is no for two basic reasons. In the first place, he argues, we cannot form any consistent idea of what this material substance could be, and in the second place, even if we could, no such material substance could "cause" or otherwise explain how our perceptions originate.

10. Why can't we form a consistent idea of material substance?

Material substance had a quite definite meaning inherited from Descartes dualism. It is supposed to be merely that which has the primary properties, but which is not itself any of those properties, nor is it capable of any thought or any spontaneous activity. While matter can and does move, it cannot itself be the cause of its motion; it is utterly inactive. It is, of course, defined in contradistinction to "mind" as being that which cannot think and cannot act, whereas mind is nothing but that which thinks and that which, through volition, acts. Now we have found that primary and secondary properties alike are all perceptions. But only things which can think can have perceptions. Therefore, to say that matter has primary properties amounts to saying that a thing which cannot think has perceptions. But having perceptions is a kind of thinking. Furthermore causing perceptions is a kind of activity. So the materialist is guilty of two self- contradictory statements: a thing which does not think has thoughts and a thing which is inactive acts. This amounts to a refutation of materialism by what is called a "reductio ad absurdum" (reduction to absurdity or contradiction).

11. Why can't we form some other idea of "material substance"?

It will be recalled that Descartes had originated the notion of "matter" or "material substance" not by appeal to perceptual experience but by appeal to an allegedly "innate idea" supplied by "reason" (the "thinking thing"). This is of course a fair move within the game of rationalist epistemology, but it leads to the mind-body problem. Berkeley has resolved not to play that game and insists on the empiricist starting point that the mind has no ideas that are not given to it by some sensory perception. Thus for an empiricist like Berkeley there can be no appeal to forming an idea of something which is unperceived.

12. Why can't I think of something existing outside the mind even if I do not know what it is?

Matter is supposed to be something that exists independently of mind, or in other words something that can exist without being perceived, or whether or not we or anyone perceives it. But since anything I can think of in my mind is, by definition, an idea, and since all ideas originate in sensory perceptions (this is of course Berkeley's empiricism), the attempt to formulate an idea of something existing "unperceived" is literally a contradiction in terms. When I think of something existing in a state where no one is perceiving it I have not proved that such a thing can exist without its being perceived, for in thinking of it, I am of course, thinking of  it, and anything I think is, of course, a perception in my mind. (I would be thinking of what it would look like if I were there perceiving it.)

13. Why can't matter be regarded as the cause of perceptions?

Aside from the fact that by Berkeley's argument this involves the inconsistent claim than an inactive thing acts, the recognition that matter cannot be the cause of perceptions amounts to the recognition that the mind-body problem as Descartes set it up is irresolvable. If the materialist argues that something must cause our perceptions, therefore we postulate that something exists outside the mind to cause these perceptions, and this, whatever it might be, is what he means by "matter," then the burden is on him (the advocate of "matter") to explain just how this "something" which cannot think causes thoughts. Berkeley considers a variety of variations on this general claim and finds that none are able to provide any explanation of this crucial issue. He therefore proposes to do away with the mind-body problem by arguing that the cause of our perceptions is not something different from them, but just something exactly like them, namely other perceptions. While it is utterly mysterious to say a perception "copies" or "represents" a material substance (a thought copies that which cannot think), there is nothing unusual or unknown about saying one idea copies another idea. The attempt of the dualist to explain thought (i.e. one's sense perceptions) by "matter" is an attempt to explain what we know (our perceptions) by what we cannot know (material substance). How can such an account ever be an "explanation"? Instead Berkeley explains what we know (our perceptions) by something else we can know, namely, other perceptions. In this way there is no need to "bridge the gap" between the two halfs of mind-matter dualism; so the mind-body problem does not arise.

14. How can we distinguish real objects from imaginary ones if they all exist in the mind?

Some perceptions respond to our will; these are the perceptions which we generate ourselves in the faculty of imagination. But others, those to which we refer when we say we see, touch, hear, taste or smell "real (non-imaginary) objects," are not responsive to our will. It is this that leads the materialist, erroneously Berkeley thinks, to conclude that real objects are not perceptions. Nor can perceptions as distinct from mere imaginations be copies of real objects, even if that similarity is limited to primary properties, for there is no way a thought can copy an unthinking thing. In fact we distinguish between imaginations and perceptions of "real" objects not by appeal to the alleged causes that lie behind them, but by the way the perceptions appear to the perceiver. The perceptions of real objects are stronger, more vivid, and exhibit more regularity and order than those of imagination, dreams, hallucinations, and such.

15. If matter can't be the cause of our perceptions of what we think are real objects, then what is?

Berkeley concludes that those perceptions which do not respond to our will must be caused by something other than our own mind and its perceptions. But since it is impossible to form an idea of anything other than a perception, the only possible cause of which we can form any idea is another perception existing not in our mind but in some other mind. Thus our perceptions of "real" objects (as opposed to imaginary objects) are caused by or are copies of the perceptions of another mind. From the order, harmony, perfection, and interrelations exhibited by these perceptions, Berkeley concludes this other mind is one of infinite power, orderliness, and goodness. It is, without further ado, claimed to be the infinite mind of God, the "omniperceiver." For Berkeley the "evidence" for God's existence is immediate in everything we perceive. The real object is God's perception, it is the "archetype" or original which is complete in every way; it is everything there is in the object. Our perception is an "ectype" or finite copy of the Divine perception, limited by our perspective and partial knowledge of what we perceive.

16. Are we ideas in God's mind?

No. We human perceivers are finite minds which perceive a limited section of reality. God of course perceives all things in all possible ways. But we are separate minds nevertheless, not ideas in minds. As distinct minds or spirits we are held to be separate and distinct from the Divine mind. What we know immediately are of course our own perceptions which reveal how things appear to us; God perceives them as they really are because what they really are, are God's perceptions. But ideas are inactive whereas minds or spirits are active. Therefore ideas cannot copy minds or spirits. Berkeley follows traditional Christian theology in keeping human spirits separate and distinct from God. In this way God is kept free of the sin and ignorance that are part of human existence.

17. What is it to exist for Berkeley?

Berkeley's metaphysics has in effect two categories of existence: perceptions and perceivers. Objects of thought, can exist only as perceptions in some mind or another. Thus the familiar Latin motto for Berkeley, "Esse est percipi." (To be is to be perceived.) But this is only half of Berkeley's metaphysics. The other half is the assertion that there are entities or substances ("thinking things") which do the perceiving. These Berkeley calls "minds" or "spirits." Thus we add to the familiar motto, the Latin words for "or perceive": "Esse est aut percipi aut percipere." (To be is either to be perceived (perceptions) or to perceive (minds). For Berkeley, unlike the materialists and dualists, the world exists exactly as we perceive it, for the very simple reason that the world is perceptions.

18. Does this mean that the scientific description of the world  is false?

No, Berkeley agrees entirely with science as he interprets it.  What he rejects is the interpretation of science by materialist and dualist philosophers who assert that science teaches us that the real world is composed of material substances moving about in an independently real space and time, and that none of this depends for its existence on perceiving minds. For Berkeley science provides a description of the regular patterns physical objects are perceived as exhibiting. These are the laws of nature discovered by science, but what they describe is not matter moving about in space and time, but rather the orderly, regular patterns in God's thoughts, for of course, physical objects are nothing more than ideas in the Divine mind.