You are going to read all of Berkeley's first dialogue between Hylas and Philonous. This first book is a sustained attack on the distinction between primary and secondary qualities. This is a distinction which we have encountered before. Descartes called colors, tastes, smells and so forth "sensible qualities" and distinguished them sharply from those qualities which belonged to the essence of body and which are known by the intellect alone, qualities such as extension, flexibility and changeability. The distinction goes back from Descartes through Galileo to Epicurus and Lucretius in the Roman World and then back to Leucippus and Democritus among the Greeks. Locke adopted the distinction from Robert Boyle and used Boyle's terminology of primary, secondary and tertiary qualities in the Essay Concerning Human Understanding.
Why is Berkeley mounting a sustained attack on this distinction? The distinction between primary and secondary qualities is a distinction between qualities which depend for their existence on the relation between an object and a perceptual apparatus, e.g. color or smell; and qualites which a things has independently of any perceiver, e.g. extension, being in motion or at rest. This distinction is of considerable philosophical interest. After all, it distinguishes for us what really objectively exists, from what is merely subjective. In that sense it distinguishes between reality and appearance. The primary/secondary quality distinction implies that material things exist independently of us, and have certain properties independently of our perceiving them. Because Berkeley objects to the claim that matter exists independently of the mind, he must show that this distinction is untenable.
At the beginning of the first dialogue, Philonous finds Hylas taking an early morning turn in the garden to think about the discourse of the night before. "Philonous" breaks up into "philo" -- "love" and "nous" -- "mind," so, "love (or perhaps "lover") of mind." Berkeley is just such a lover of mind, and we should take Philonous as his spoksperson. "Hylas" means "matter" (in ancient Greek it means "wood" so I am sometimes tempted to translate "Hylas" as "blockhead" -- but "matter" is more likely Berkeley's intent.). Berkeley intends to deny the existence of matter, so Hylas is the spoksperson for the views which Berkeley disagrees with. So, you can take a shrewd guess at who is going to give the best arguments and convince the other! Would you like to make a prediction?
Is there any significance to the dialogue taking place in the garden at dawn? Well, it is likely that there is. The distinction between primary and secondary qualities is reductive. That is, proponents of the distinction hold that only the primary qualities are real, while the secondary are mere appearance. Philonous remarks: "That purple sky, those wild but sweet notes of birds, the fragrant bloom upon the trees and flowers, the gentle influence of the rising sun, these and a thousand nameless beauties of nature inspire the soul with secret transports, its faculties at the same time being fresh and lively, are fit for these meditations..." Note that the reference in the description are to colors, sounds, smells and the feeling produced by the rising sun -- secondary qualities all. (In fact, Berkeley makes a reference to the colors in the clouds on Pg. 230. Thus this dramatic setting is explicitly integrated into the philosophic argument of the dialogue.) Berkeley is making the point that these produce an effect on the soul -- a good effect. It turns out that the reductionism of the mechanical philosophy and the distinction between primary and secondary qualities has a bad effect on the soul. It is this which Berkeley is combatting.
(Pg. 218) Hylas then proposes to explain to Philonous what he has been thinking about, and it turns out that it is the negative effects of those who believe certain doctrines on the rest of mankind that Hylas is thinking about! In particular Hylas is worried about those who distinguish themselves from the ordinary run of mankind (the vulgar) by claiming to believe nothing at all or to believe the most extravagant things in the world, that is -- skeptics.
connection between skepticism and atheism.
Philonous agrees with Hylas, about the ill effects of the "affected doubts of some philosophers and the fantastic conceits of others" and claims that he himself has gone through an enlightening conversion by giving up some of the "sublime notions" he had gotten from the schools for vulgar opinions based on nature and common sense. (There is a nice irony here, for the dialogue begins with Hylas holding those very views which Philonous here says he has rejected!) Hylas is surprised, and remarks that he is glad to hear that there is nothing to the accounts which he had heard of Philonous the night before. Philonous asks what these accounts were. Hylas replies: "You were represented in last night's conversation as one who maintained the most extravagant opinion that ever entered into the mind of man, to wit, that there is no such thing as material substance in the world." Philonous replies that he does indeed hold this opinion, but sees nothing absurd or skeptical in it as he does in the contrary opinion (namely that there is such a thing as "material substance in the world"). Hylas replies that this is a fantastical idea which is repugnant to common sense and a manifest piece of skepticism! Philonous replies "What if it should prove, that you who hold that it is, are by virtue of that opinion a greater skeptic, and maintain more paradoxes and repugnencies to common sense, than I who believe no such thing?" So, the issue is joined -- Does the doctrine that material substance exists lead to skepticism and thus atheism, or is it the contrary opinion which has this effect?
(Pg. 220) The next question, naturally, is what "sensible things" are. This is a crucial point in the dialogue. If you miss how this goes, you will fail to understand much of what happens later. So pay attention here! Philonous asks Hylas what he means by sensible things.
immediate versus mediated perception
It seems then that by sensible things you mean those only which can be perceived immediately by sense.
Phil. "In reading a book what I immediately perceive are the letters, but mediately, or by means of these are suggested to my mind the notions of God, virtue, truth etc. Now that the letters are truly sensible things, or perceived by sense, there is no doubt: but I would know whether you take the things suggested by them to be so to.
Hyl. "No, certainly it were absurd to think God or virtue sensible things, though they be signified and suggested to the mind by sensible marks, with which they have an arbitrary connection."
Philonous is now going to draw out the consequences of this distinction. It turns out that what one immediately perceives are light, colors, figures, sounds, odors, and tangible qualities such as heat and weight. The causes of such qualities, whatever they are are not perceived immediately, and so are not sensible things. Having gotten these admissions Philonous has enough to show that matter is not a sensible thing. We will get to this by the by.
Berkeley now turns to his own most important principle. On Pg. 221 Philonous asks Hylas if sensible things are not just "so many sensible qualites, or combinations of sensible qualities." This definition is intended to contrast with something like Locke's definition of substance, which requires a substratum to support the combination of sensible qualites, and which we infer to exist, because there seems to be no way a quality like whiteness can subsist without support. Hylas, however, agrees with Berkeley that sensible things are just combinations of sensible qualities. Now Philonous, having gotten Hylas to agree that heat is a sensible quality, remarks: "Doth the reality of sensible things consist in being perceived? or is it something distinct from being perceived, and that bears no relation to the mind?" This leads Philonous to ennunciate one of Berkeley's most important principles -- esse est percipi vel percipere -- to be is to perceive or to be perceived. Hylas, in this case, does not agree. Instead he says: "To exist is one thing, to be perceived is another."
From Pg. 221 to Pg. 233 Hylas defends the reality independent of the perceiver of heat (Pp. 221-225), tastes (Pp. 225-226), odors (Pp. 226-227), sounds (Pp. 227-29), colors and light (Pg. 229- 233). There are a number of interesting features of these arguments.
Now we want to look at some of the particulars of the arguments which Berkeley offers to show that qualities such as heat, odors, tastes, sounds and colors are all mind dependent. The arguments about heat are the first, and set the pattern for the rest, though there is some variation. Another reason for going over the section on heat carefully is that it has several parts. Rereading this section, I found myself at the end confused about what Berkeley had just done. The way to avoid such confusion is to sort out the parts. It turns out that between Pg. 221 and Pg. 225 Berkeley gives five distinct arguments related to heat and cold. If you do not distinguish these you are very likely going to mix them together, and hence end up confused! There are two main sections. The first has to do with extreme heat (the first three arguments), and the second with moderate heat and cold (the next two arguments). There is a final argument which goes back to issues about extreme heat.
On Pg. 221 Berkeley begins with heat. First he establishes that it is a sensible quality. He raises the issues about whether to be is to be perceived in terms of heat. He continues:
Phil. "I speak with regard to sensible qualities only; and of these I ask, whether by their real existence you mean a subsistence exterior to the mind, and distinct from their being perceived?"
Hyl. "I mean a real absolute being, distinct from, and without any relation to their being perceived."
Phil. "Heat, therefore, if it is to be allowed a real being, must exist without the mind.
Hyl. "It must."
So, here is the issue about heat. Is it a mind dependent quality which only exists in relation to some perceiver, or is it a quality which exists independently of the mind, and which can be perceived or not perceived as the case may be.
Berkeley now begins by considering degrees of heat. This is because he plans to connect heat and cold with pleasure and pain. Can you figure out why he would try to do this? First, he gets Hylas to agree that real existence is compatible with all degrees of heat which we perceive and not just some.
|Heat is mind dependent|
the first argument
line 1 Phil. "But is not the most vehement and intense degree of heat a very great pain?
line 2 Hyl. "No one can deny it."
line 3 Phil. "And is any unperceiving thing capable of pain or pleasure?
line 4 Hyl. "No, certainly."
line 5 Phil. "Is your material substance a senseless being, or a being endowed with sense and perception."
line 6 Hyl. "It is senseless without doubt."
line 7 Phil. "It cannot therefore be the subject of pain.
line 8 Hyl. "By no means."
line 9 Phil. "Nor consequently of the greatest heat perceived by sense, since you acknowledge this to be no small pain.
line 10 Hyl. "I grant it."
line 11 Phil. "What shall we say then, of your external object; is it a material substance or no?"
line 12 Hyl. "It is a material substance with the sensible qualities inhering in it."
line 13 Phil. "How then, can a great heat exist in it, since you own it cannot [be] in a material substance? I would desire you would clear this point.
What we have here is an argument. Its conclusion is that heat cannot exist in a material substance. If we put this argument in the standard form for argument reconstruction, it will look like this:
|P1. The most vehement and intense degree of heat is an intense pain.|
|P2. No unperceiving thing is capable of feeling pleasure or pain.|
|P3. Material substance is senseless and unperceiving. Therefore:|
|P4. Material substance not capable of feeling pain.||(From 2 and 3)|
|P5. Material substance is not capable of feeling the greatest heat perceived by sense.||(from 1 and 4)|
|P6. Ex hypothesi: The external object which has heat in it corresponding to the heat which we perceive is a material substance with sensible qualities inhering in it.|
|P. 7. Such a material substance cannot have a great heat in it.||from 5 and 6|
|Cl. 8 So heat cannot exist in an external object or material substance but must exist in something which senses and perceives.||from lines 2, 6 and 7|
Note how this reconstruction was done. P1 is derived from lines 1 and 2 where Philonous asks whether intense heat is a pain and Hylas agrees. Since Hylas agrees we can take it as established as a truth -- hence Premise 1. In the same way, P2 is derived from lines 3 and 4, P3 from lines 5 and 6. The "therefore" before P4 indicates that we are getting an intermediate conclusion derived from previous premises. This intermediate conclusion itself serves as a premise, and so is listed as P4. P5 is (as indicated) derived from P1 and P4. The hypothesis refered to in P6 is: "Whatever degree of heat we perceive by sense, we may be sure the same exists in the object that occasions it." It is this view which Berkeley aims to show cannot be maintained. P6 is derived from this sentence and lines 11 and 12. P7 derives the contradiction of the hypothesis. Cl 8 -- the main conclusion, is that the hypothesis cannot be true, and (by implication) the competing hypothesis that heat is a mind dependent quality must therefore be true. This is the point which Philonous wants Hylas to "clear" -- that is explain.
Hylas responds by claiming that he should not have agreed to the truth of the first premise of the argument -- that intense heat is a great pain. He says: "Hold Philonous, I fear I was out in yielding intense heat to be a pain. It should seem rather, that pain is something distinct from heat, and the consequence or effect of it." Good going Hylas! This is a much more reasonable position to defend.
|Heat is mind dependent|
the second argument
line 1: Phil. Upon putting your hand near the fire, do you perceive one simple uniform sensation, or two distinct sensations?
line 2: Hyl. But one simple sensation.
line 3: Phil. Is not the heat immediately perceived?
line 4: Hyl. It is.
line 5: Phil. And the pain?
line 6: Hyl. True.
line 7: Phil. Seeing that they are both immediately perceived at the same time, and the fire affects you with only one, simple, or uncompounded idea, it follows that this same simple idea is both the intense heat immediately perceived, and the pain; and consequently, that the intense heat immediately perceived, is nothing distinct from a particular sort of pain.
Line 7 gives the argument, it picks up all the preceeding premises and draws the conclusion that the intense heat is identical with the pain. It follows that they are not distinct, and so Hylas revised claim that they are distinct, and in fact stand in the relation of cause to effect, must be false. You should now follow the pattern of reconstruction which I described above and reconstruct this argument. The first question you should ask yourself is: "What is the main conclusion?" All the rest will be premises.
One of the beauties of engaging in the process of sorting out the different parts of a passage like this, and reconstructing arguments, is that it puts you in a position to evaluate the arguments given. My suspicion is that this last argument is rather weak. If I were going to write a paper, arguing against Berkeley about heat, I would very likely focus my attention on this argument.
|Heat is mind dependent|
the third argument
Philonous goes on to give yet another argument. He says (beginning at the top of Pg. 223):
line 1 Phil. Again, try in your thoughts, Hylas, if you can conceive a vehement sensation to be without pain or pleasure.
line 2 Hyl. I cannot.
line 3 Phil. Or can you frame to yourself an idea of sensible pain or pleasure in general, abstracted from every particular idea of heat, cold, tastes, smells, &?
line 4 Hyl. I do not find that I can
line 5 Phil. Doth it not therefore follow, that sensible pain is nothing distinct from those sensations or ideas, in an intense degree?
line 6 Hy. It is undeniable; and to speak the truth, I begin to suspect that a very great heat cannot exist but in a mind perceiving it.
How do we know this is another argument? One reason is that Philonous had already reached the conclusion that heat and pain are not distinct. So this part is not needed for that argument. And Philonous begins by saying "Again..." which suggests an additional consideration. Finally this argument is about abstraction, which had not been mentioned in the previous argument. So, the content is different. These give us good reasons to take this as a separate argument.
Abstraction is one of Berkeley's bug-a-boos. Abstracting is a process which Locke describes of leaving out various elements in an idea so that it applies to more than one individual or class. If you think of the way a classificatory system works -- say the class of trees, you can see how this works. Some trees are deciduous, some are evergreen. You must leave out these characteristics if you want to give a definition which includes both. Berkeley things one can have general ideas, but not abstract general ideas. On his view, every general idea is a particular idea which is used to refer to a whole group. Related to the view that there is not such thing as an abstract general idea is another one -- that all ideas are images. If you have an image of some particular triangle, it will either be right angled, isosceles, or scalene. Now try to come up with an image of a triangle which combines or leaves out these properties. It cannot be done. You may have a definition in words which is not an image -- like a triangle is any enclosed plane figure made up of three straight lines and three angles -- but for Berkeley that does not count as an idea! Berkeley is convinced that there is no such thing as an abstract general idea, and he thinks that philosophers like Locke who think that there are such things are deluding themselves and that this delusion leads to serious errors -- like thinking that things can exist without being perceived.
|Summary of the section on intense heat ---|
|"...because intense heat is nothing else than a particular kind of painful sensation; and pain cannot exist but in a perceiving being, it follows that no intense heat can exist in an unperceiving corporeal substance."|
One might now think that we have had enough effort to show that heat is a mind dependent quality and that we can go on to some other quality. But Berkeley is just getting going. Philonous has gotten Hylas to agree that intense heat must be mind dependent, but he is not going to agree that lesser degrees of heat are! This may be somewhat surprising as Philonous was careful at the beginning to get Hylas to agree that real existence was compatible with all degrees of heat and not just some. But now Hylas is going to go back on that agreement! Why would Berkeley have Hylas do this? Well, so that now, having established to his own satisfaction that intense heat can only exist in the mind, he can deal with those who would not be inclined to make the concession which Hylas made at first. And this also shows one of the virtues of a philosopher engaged in the search for truth! If your opponent makes a slip which he then recognizes, let him change his position. Thus Berkeley can take a step towards refuting all the available positions and be philosophically virtuous at the same time!
Phil. Is it therefore certain, that there is no body in nature really hot?
Hyl. I have not denied that there is any real heat in bodies. I only say that there is no such thing as an intense real heat.
Phil. But did you not say before, that all degrees of heat were equally real: or if there was any difference, that the greater were more undoubtedly real than the lesser?
Hyl. True, but it was because I did not then consider the ground there is for distinguishing between them, which I now plainly see. And it is this: because intense heat is nothing else than a particular kind of painful sensation; and pain cannot exist but in a perceiving being, it follows that no intense heat can exist in an unperceiving corporeal substance. But this is no reason why we should deny heat in an inferior degree to exist in such a substance.
Philonous goes on to ask how we are going to distinguish those degrees of heat which can exist only in the mind from those which cannot. Hylas replies that this is easy, the ones which cause pain, even a little pain, can exist only in the mind, the rest not. Im response, Philonous now turns from examining the connection of pain with heat to pleasure and heat and cold as well. On Pg. 224 Hylas in answer to Philonous questionns works out his new position. Intense heat and intense cold cannot exist in external bodies because they are pains. A slight warmth or cold can exist in an external object because it is neither a pleasure or a pain, but rather what Hylas calls an indolence --nothing more than a privation of both pleasure and pain. He is dirven to this because if he admits a a slight warmth or cold is a pleasure or pain, he will be forced to admit that these cannot exist in a material substance because of the previous arguments about intense heat.
Finally Philonous sums up the new position:
Phil. Those bodies, therefore, upon whose application to our own we perceive a moderate degree of heat, must be concluded to have a moderate degree of warmth in them; and those upon whose application we feel a like degree of cold, must be thought to have cold in them.
|Heat is mind dependent|
the fourth argument
Phil. Can any doctrine be true that necessarily leads a man into an absurdity?
Hyl. Without doubt it cannot.
Phil. Is it not an absurdity to think that the same thing should be at the same time both cold and warm?
Hyl. It is.
Phil. Suppose now one of your hands hot and the other cold, and that they are both at once put into the same vessel of water, in an intermediate state, will not the water seem cold to one hand and warm to the other?
Hyl. It will.
Phil. Ought we not therefore by your principles to conclude, it is really both cold and warm at the same time, that is, according to your concession, to believe an absurdity?
Hyl. I confess it seems so.
Let us reconstruct this argument in the way in which we did the others.
P1. Any docrtine which necessarily leads a person into an absurdity cannot be true.
P2. To claim that the same thing should be at the same time both cold and warm is just such an absurdity.
P3. Those bodies upon whose application to our own we perceive a moderate degree of heat, must be concluded to have a moderate degree of warmth in them; and those upon whose application we feel a like degree of cold, must be thought to have cold in them. (Hylas' hypothesis)
P4. If one puts a hot hand and a cold hand into water in an intermediate state, the water will seem cold to one hand and warm to the other.
P5. One ought to conclude from Hylas' principles that the water in fact is both warm and cold. (From P3 and P4)
P6. But this (P5) is precisely what was admitted to be an absurdity. (P2)
Cl 7 Therefore, the hypothesis (P3 must be false.
One point of interest is that this argument fits the standard form of skeptical reasoning. Consider, for example, P2. This is simply a version of the standard skeptical principle that reality must be consistent and non-contradictory. The remainder of the argument goes to show that what we experience (in this case heat and cold) does not have this character. So, one might conclude that our experience of heat and cold only gives us appearance and not reality. It is quite plain from the introduction to the first dialogue that Berkeley does not in the least consider himself a skeptic. In fact he thinks that the corpuscular philosophy of Locke, Boyle and Newton which he is opposing is skeptical and leads to atheism. So, why would Berkeley use what are clearly skeptical arguments? The answer is that Berkeley and the skeptics go a certain way along the road together, and then they part company.
On Pg. 225 Berkeley gives one final argument to show that heat is a mind dependent quality.
|Heat is mind dependent|
the fifth argument
Phil. When a pin pricks your fingers, does it not divde and rend the fibers of your flesh?
Hyl. It doth.
Phil. And when a coal burns your finger, doth it any more?
Hyl. It doth not.
Phil. Since therefore you do not judge the sensation itself occasioned by the pin, nor anything like it to be in the pin, you should not, conformably to what you have now granted, judge the sensation occasioned by the fire, or anything like it, to be in the fire.
Hyl. Well, since it must be so, I am content to yield this point, and acknowledge, that heat and cold are only sensations existing in our minds; but there still remains qualities enough to secure the reality of external things.
Reconstructing this argument, you get something like this:
P1. In two cases exactly alike, we ought to make the same judgement.
P2. When a pin pricks your finger, it divides and rends the fibers of your flesh.
P3. When a coal burns your finger, it does exactly the same.
[P4. The pin is an unperceiving and unsensing thing and cannot feel pain]
P5. In regard to the pin, you make the judgement that the sensations itself occasioned by the pin and anything like it, are not in the pin itself.
Cl. 6 Therefore, you should conclude that the sensation itself occasioned by the fire and anything like it, are not in the fire.
At this point Hylas gives in about heat and cold but announces that the still remain "qualities enough to secure the reality of external things." Philonous replies: "But what will you say, Hylas, if it shall appear that the case is the same with regard to all other sensible qualities?" That is what remains to be shown.
Having dealt with heat and cold, Bekeley, as noted earlier takes up the rest of a list of secondary qualities; tastes (Pp. 225-226), odors (Pp. 226-227), sounds (Pp. 227-29), colors and light (Pg. 229- 233). As you can see from these page references, these each get a somewhat less thorough going over than heat did. The reason for this is the one just noted, that Berkeley thinks the case is the same with regard to all of them. I am going to skip a detailed analysis of these sections for you to do as an exercise. I. Reconstructing an argument.
One question we should consider is why Berkeley gives all these arguments about secondary qualities at all? Why does he have Hylas maintain the reality independent of the mind of what philosophers from Galileo to Locke had called secondary qualities? These philosophers had denied the independent reality of secondary qualities. So, in effect, Berkeley makes Hylas start out holding the position, not of the "modern" philosophers, but of the Schools. The Schools (sometimes called the Scholastics) were the dominant force in the Universities. They held an Aristotelian view of perception which claimed that all qualities are real and exist independent of the mind. Galileo, Descartes, Boyle and Locke all rejected the Scholastic view, and were at pains to show that this is not true of a whole set of qualites -- the set of qualities which Descartes calls "sensible qualities" and which Boyle and Locke refer to as secondary qualities. Berkeley is repeating the arguments of these philosophers and perhaps going into even more detail than they do in making these arguments. Since he agrees with them about the nature of these qualities, why recapitulate the arguments in great detail? The answer has to do with the nature of dialogue. I suggest you consult the section on "Dialogue" in the OSU Philsophy Department Writing Philosophy Papers: A Student Guide for an explanation.
On Pp. 233-4 we get to the heart of what the first dialogue is all about. Hylas is at last forced to make the distinction between primary and secondary qualities, and Philonous tells him the strategy he is going to follow to show that the distinction is not tenable. Berkeley is going to show that the same kind of arguments which show that the so called secondary qualities are mind dependent apply to the primary qualities as well, and so no distinction can be drawn between them --at least on the basis of empirical evidence. Here we have, at least in part, the justification for the detailed arguments going to show that secondary qualities are mind dependent. They are going to serve as the model for showing the same result applies to primary qualities. And the beauty of it is, that the other side, Descartes, Boyle and Locke -- all of whom make the distinction to which Berkeley objects, all accept the arguments in the model! Here is what Berkeley writes:
Phil. You are still then of the opinion, that extension and figure are inherent in external unthinking substances.So, there it is, that is the main conclusion which this whole first dialogue is aimed to establish.
Hylas I am.
Phil. But what if the same arguments which are brought against secondary qualities, will hold proof against these also?
Hylas Why then I shall be obliged to think, they too exist only in the mind
On Pp. 234-236 Berkely deals with figure and extension together. On Pg. 236 he takes up motion, then on Pg. 237 (towards the bottom) returns to extension, when Hylas makes a distinction between "absolute and sensible extension" and which leads to a discussion of abstraction and the ideas of "extension in general and motion in general." This discussion continues up to Pg. 240. There Hylas makes yet another distinction, between the sensation of something and the object which causes the sensation. This leads (Pg. 241) to a distinction between two elements in perception, active and passive. This ends towards the bottom of Pg. 242. Hylas then makes another distinction, between qualities and modes, on the one hand and substances or substratum on the other. The substratum or substance is necessary to support the qualities. Philonous finishes with this on Pg. 244. Hylas then (at the bottom of Pg. 244) makes the suggestion that the problem is that Philonous took the qualities separately, rather than together. This continues until the top of Pg. 246. Hylas then introduces some new problems. The first of these is the claim that we see objects at a distance. Philonous finishes with this on Pg. 248. Hylas brings up the causal or representational theory of perception. This finishes on Pg. 251.Philonous then concludes that he has demonstrated from Hylas' principles that Hylas is a skeptic. Hylas admits that while he is not entirely convinced, for the present he is silenced. They agree to meet again the next day to reconsider the matter.
So, it turns out that the actual analysis of primary qualities is much more brief than that of the secondary qualities. The arguments about extension, figure and motion go for about three pages. Then Hylas starts make distinctions which lead to the discussion of abstraction, of the active and passive elements in perception (with the conclusion that perception is purely passive), and the discussion of the doctrine of substance and substratum. (Here we have an attack on Locke's account of material substance, using Locke's own doubts about the cogency of the concept to conclude that it is incoherent! Yet Berkeley believes in immaterial substances!) The discussion of whether qualites together can exist outside of the mind leads to the assertion of one of Berkeley's most fundamental claims, that to be is to perceive or be perceived, and that no thing can exist unperceived. Then we get the discussion of seeing at a distance. If we actually immediately see things at a distance, that suggests that extension exists independently of the mind. Berkeley had dealt with that problem in his first book A New Theory of Vision, and his conclusion is that we do not immediately perceive distance, we infer it. Finally, he takes up the representational or causal theory of perception and demonstrates some fundamental problems in it, at least interpreted in the way in which he interprets it. In effect we get the problem of the "veil of perception" -- that because we see ideas, we do not see objects, and hence there is no basis for saying the ideas resemble the objects which cause them. In fact, in principle, we cannot experience such objects. Nor do we have any reason to say that they exist.
Having taken up all this time in examining Berkeley's attacks on the mechanical philosophers, materialists and dualists, we should consider Berkeley's own account of things in the external world. It is plain that Berkeley does not belive that there is any such thing as matter or material substance existing indpendently of us. What then is a thing? The answer is largely contained in Berkeley's definition of sensible things, given earlier. "It seems then that by sensible things you mean those only which can be perceived immediately by sense." He then goes on to note that we immediately perceive by sight light, colours, and figures; by hearing, sounds; by the palate, tastes; by the smell, odours; and by the touch, tangible qualities. So, a thing for Berkeley is simply a collection of sensible qualities which are mind dependent. So to be a sensible thing is to be a collection of sensible qualities perceived by some mind. The advantage to this view of sensible things becomes clear if we go back to Descartes and recall that for Descartes it was certain that he seemed to see a fire and a piece of paper and some hands in front of him. What he could not be certain of was that these ideas acutally corresponded to the situation in the world. He might have hands but he might be in bed, or perhaps he did not have a body at all. Perhaps there was a fire and a piece of paper, but perhaps not. In order to resolve these doubts, Descartes has to engage in heroics. He has to prove the existence of God, trace the connection of mathematics through the understanding and imagination, prove the existence of external objects, and so on. Berkeley removes these difficulties at one fell swoop, by making the ideas we perceive for certain the very things themselves. Berkeley saw his positive account of things as collections of sensible ideas as the vindication of common sense against skepticism, and consequently atheism. There is, however, a clear difficulty with this. Common sense tells us that objects in the external world exist and persist independently of us. When we look the other way, trees do not just go out of existence. And what about the unperceived beams above the ceiling which are holding up the roof? Dr. Johnson once begged a Berkelian not to leave his group, for he said, they might stop thinking of him and he would go out of existence! Of course, this is not right, for the Berkelian was a perceiver, and so did not need to be perceived in order to exist. But it gives you a sense of the difficulty. Berkeley's response to this is clever. It is here that we can advantageously turn to limericks to get the full effect of this Irish philosophy: There was a young man who said "God, must think it exceedingly odd If he finds that this tree continues to be When there is no one about in the Quad." Reply: Dear Sir, Your astonishment's odd: I am always about in the Quad. And that's why the tree Will continue to be, Since observed by Yours faithfully, God