Context

In the first two Sections of Part IV, the author has considered the bases of skepticism regarding the probabilistic inferences of reason and the faith we place in our senses. He ends by presuming that an external world exists and proceeds to examine two systems that attempt to account for its nature. The previous Section concerns the ancient systems that describe external objects as substances consisting of original matter, substantial form, and accidents. The present Section considers the modern system that rejects those categories in favor of a distinction between a body and its qualities, with a further distinction among qualities between those that are primary and those which are secondary.

Background

The modern revolt against the ancient systems began early in the seventeenth century with such thinkers as Descartes and Hobbes. In his 1641 Meditations, Descartes resolved only to accept as true what he could not doubt, and he discovered that he could not doubt that which he perceived clearly and distinctly. He then applied this criterion to the qualities of corporeal objects.

As belonging to the class of things that are clearly apprehended, I recognize the following, viz, magnitude or extension in length, breadth, and depth; figure, which results from the termination of extension; situation, which bodies of diverse figures preserve with reference to each other; and motion or the change of situation; to which may be added substance, duration, and number. But with regard to light, colors, sounds, odors, tastes, heat, cold, and the other tactile qualities, they are thought with so much obscurity and confusion, that I cannot determine even whether they are true or false; in other words, whether or not the ideas I have of these qualities are in truth the ideas of real objects. (Meditation Three)

And, though on approaching the fire I feel heat, and even pain on approaching it too closely, I have, however, from this no ground for holding that something resembling the heat I feel is in the fire, any more than that there is something similar to the pain; all that I have ground for believing is, that there is something in it, whatever it may be, which excites in me those sensations of heat or pain.

[T]o extended substance we refer magnitude, or extension in length, breadth, and depth, figure, motion, situation, divisibility of parts themselves, and the like. There are, however, besides these, certain things of which we have an internal experience that ought not to be referred either to the mind of itself, or to the body alone, but to the close and intimate union between them . . . . Of this class are . . . all the sensations, as of pain, titillation, light and colours, sounds, smells, tastes, heat, hardness, and the other tactile qualities.

John Locke’s 1689 An Essay concerning Human Understanding, Book II, Chapter 8, makes a similar distinction, describing the former class of qualities as primary and the latter as secondary. Locke first distinguished between ideas in the mind and powers in bodies to produce such ideas, which he called qualities of the bodies. Primary qualities are those that

are utterly inseparable from the body, in what state soever it be; and such as in all the alterations and changes it suffers, all the force can be used upon it, it constantly keeps; and such as sense constantly finds in every particle of matter which has bulk enough to be perceived; and the mind finds inseparable from every particle of matter, though less than to make itself singly be perceived by our senses . . . .

such qualities which in truth are nothing in the objects themselves but powers to produce various sensations in us by their primary qualities, i.e. by the bulk, figure, texture, and motion of their insensible parts, as colours, sounds, tastes, &c.

The distinction between primary and secondary qualities of bodies was attacked by Berkeley in his Principles of Human Knowledge (1710) and Three Dialogues between Hylas and Philonous (1713). In Section 9 of the former work, Berkeley describes the distinction.

Some there are who make a distinction betwixt primary and secondary qualities. By the former they mean extension, figure, motion, rest, solidity or impenetrability, and number; by the latter they denote all other sensible qualities, as colours, sounds, tastes, and so forth. The ideas we have of these they acknowledge not to be the resemblances of anything existing without the mind, or unperceived, but they will have our ideas of the primary qualities to be patterns or images of things which exist without the mind, in an unthinking substance which they call Matter.

Now, if it be certain that those original qualities are inseparably united with the other sensible qualities, and not, even in thought, capable of being abstracted from them, it plainly follows that they exist only in the mind. But I desire any one to reflect and try whether he can, by any abstraction of thought, conceive the extension and motion of a body without all other sensible qualities. For my own part, I see evidently that it is not in my power to frame an idea of a body extended and moving, but I must withal give it some colour or other sensible quality which is acknowledged to exist only in the mind. In short, extension, figure, and motion, abstracted from all other qualities, are inconceivable. Where therefore the other sensible qualities are, there must these be also, to wit, in the mind and nowhere else.

that which at other times seems sweet, shall, to a distempered palate, appear bitter. And, nothing can be plainer than that divers persons perceive different tastes in the same food; since that which one man delights in, another abhors. And how could this be, if the taste was something really inherent in the food?

in case colours were real properties or affections inherent in external bodies, they could admit of no alteration without some change wrought in the very bodies themselves: but, is it not evident from what hath been said that, upon the use of microscopes, upon a change happening in the humours of the eye, or a variation of distance, without any manner of real alteration in the thing itself, the colours of any object are either changed, or totally disappear? Nay, all other circumstances remaining the same, change but the situation of some objects, and they shall present different colours to the eye.

The Treatise

1. A potential objection to the author’s system is that it overtly relies on the imagination as the ultimate judge of all systems of philosophy. He has in the last Section condemned the ancient system on the grounds that it is entirely guided in its reasonings by the imagination. [So if the imagination is the criterion for judging the worth of a system, how can the system’s reliance on it be consistently criticized?] The author responds by distinguishing between two kinds of use of the imagination. The first use leads to “principles which are permanent, irresistible, and universal,” e.g. the customary transition from cause to effect and vice-versa. Their removal would mean the perishing and ruin of human nature. The second use, as in the ancient philosophy, leads to principles which are “changeable, weak, and irregular.” These are “neither unavoidable to mankind, nor necessary, or so much as useful in the conduct of life; but on the contrary are observ’d only to take place in weak minds, and being opposite to the other principles of custom and reasoning, may easily be subverted by a due contrast and opposition.” This difference leads philosophers to embrace the former kind of principle and reject the latter kind. For example, one makes a just and natural inference from hearing a voice in the dark to the belief in the presence of another person, despite the fact that this conclusion be deriv’d from nothing but custom, which infixes and enlivens the idea of a human creature, on account of his usual conjunction with the present impression. But someone who, for unknown reasons, is tormented by imaginary ghosts in the dark may also be said to reason naturally. What is natural is not necessarily a good thing, however, and the naturalness of this kind of reasoning is akin to that of the naturalness of an illness, which is “contrary to health, the most agreeable and most natural situation of man.”

2. The fictions of the ancient system, such as substance and accident are like specters in the dark, and their reasonings to the existence of substantial forms and occult qualities are like those of the tormented person, deriv’d from principles, which, however common, are neither universal nor unavoidable in human nature. The modern philosophy attempts to repudiate such weak and irregular principles of the imagination and embrace only those that are solid, permanent, and consistent. The author will now examine the grounds for this pretension.

3. According to the author, [t]he fundamental principle of that philosophy [the modern] is the opinion concerning colours, sounds, tastes, smells, heat and cold; which it assert to be nothing but impressions in the mind, deriv’d from the operation of external objects, and without any resemblance to the qualities of those objects. [Thus, the nature of the primary qualities is not taken by the author to be fundamental.] The author endorses only one of the arguments commonly given for this conclusion. The basis of the argument is the fact that the impressions of colors, sounds, etc. vary considerably while to all appearance the object remains the same. A number of instances of this relativity are cited.

• Different conditions of our health,
• Complexions and constitutions of different people,
• Difference in people’s situation and position.

4. From these instances of relativity, we may draw a conclusion which is “likewise as satisfactory as can possibly be imagin’d.” Suppose an object appears differently to the same sense [of different persons] at the same time. Not all of those impressions can resemble what is in the object itself. For as the same object cannot, at the same time, be endow’d with different qualities of the same sense, and as the same quality cannot resemble impressions entirely different; it evidently follows, that many of our impressions have no external model or archetype. [Take, for example, different impressions of color of a single object had by two different people at one time. The object cannot be both of those different colors at once, nor can the quality of the object resemble both impressions at once. In that case, at least one of the two impressions does not resemble the object, which is to say that the object is not the model or archetype of that impression.] The author now appeals to the principle [laid down in Part III, Section 15] that we presume like effects to have like causes. It has just been established that some impressions, such as of colors, do not resemble their objects. Philosophers have taken the origin of these impressions to be internal to the mind. Now there is nothing in the appearance of these impressions that distinguishes them from any others of the same kind. So all colors, etc., must be presumed to have the same kind of cause.

5. It appears to follow as an easy consequence of this view that once we remove colors, sounds, etc. from the ranks of what really exist, the only real qualities of which we have any kind of adequate conception are the so-called primary qualities. These primary qualities are extension and solidity, with their different mixtures and modifications; figure, motion, gravity, and cohesion. These qualities are supposed to explain all changes in bodies, whether physical or biological. One figure and motion produces another figure and motion; nor does there remain in the material universe any other principle, either active or passive, of which we can form the most distant idea.

6. Although the author thinks that many objections may be made to this system, he regards one as in my opinion very decisive. The objection is that rather than explaining how external things operate, this reasoning will “utterly annihilate all these objects, and reduce ourselves to the opinions of the most extravagant scepticism concerning them.” Given that colors, sounds, and their mates are merely perceptions, nothing we can conceive is possest of a real, continu’d, and independent existence; not even motion, extension and solidity, which are the primary qualities chiefly insisted on.

7. [In this and the following two paragraphs, the author will examine successively the qualities of motion, extension, and solidity.] To begin with motion, there is no way to conceive of motion without reference to a body. The idea of motion necessarily suggests that of a body moving. The idea of a body, in turn, must be understood in terms of extension or solidity, and consequently the reality of motion depends upon that of those other qualities. [Thus, only extension and solidity remain as candidates for real, continued, and independent existence.]

8. The author has already, in Part II, Section 3, shown that extension must be conceived as composed of parts, whether they be colored [visible] or solid [tangible]. Thus there is a dependence of extension on some other quality, just as motion is dependent on another quality—something that is acknowledged by all. Here, the author summarizes his previous argument. By the very nature of extension, every extended thing is composed of parts. These parts may be extended, but if so, they also have parts. Ultimately, there must be some parts which are perfectly simple and indivisible. Since they are not extended, these parts would be nothing unless they had some other quality, such as being colored or being solid. But the doctrine of the modern philosophers excludes color from real existence, so the only quality remaining is solidity. The reality, therefore, of our idea of extension depends upon the reality of that of solidity, nor can the former be just while the latter is chimerical. Thus, the author must now examine the one remaining quality of the trio, solidity, to determine whether it exists independently.

9. The idea of solidity is that of the continued separate existence of two objects which are impelled toward each other with the utmost force, rather than their inter-penetration. Thus, the idea of solidity is based on that of solid bodies which maintain their separate existence upon contact. So we now need the idea of body to explain that of solidity. But this idea of body cannot be based on secondary qualities, which are admitted not to belong to them. The idea of motion has been shown to depend on that of extension, and that of extension has been shown to depend on the idea of solidity. ’Tis impossible, therefore, that the idea of solidity can depend on either of them. For that woul’d be to run in a circle, and make one idea depend on another, while at the same time the latter depends on the former. Thus, because the modern philosophy cannot give us a just or satisfactory idea of solidity, it gives us none of matter.

10. Although the author believes that the argument will be entirely conclusive to every one that comprehends it, he recognizes that the general reader may have trouble with it, so he will try to make it more obvious by presenting it in other words. The idea of solidity requires conceiving two bodies pressing on each other with no penetration. We cannot conceive of such a situation without conceiving of two bodies, let alone without conceiving of any bodies at all. If we conceive of two non-entities, we cannot assign them any place, or any other quality, for that matter, so they cannot be thought to exclude each other from a place. Now, I ask, what idea do we form of these bodies or objects, to which we suppose solidity to belong? If we say that the idea is formed from the idea of solidity, then the argument can be re-cycled: the idea of solidity supposes that of body, which supposes an idea of solidity, and so on in infinitum. If we say that the idea of body is formed from that of extension, then, we either have run into a false idea [of colored extension] or we must argue in a circle [since extension depends on solidity, which depends on extension]. Extension cannot be colored, since color is a secondary quality that is supposed to be unreal. The same point applies to the other primary qualities of mobility and figure. [Mobility and figure both depend on extension, at which point the dilemma just raised applies anew.] So on the whole, after the exclusion of colours, sounds, heat and cold from the ranks of external existences, there remains nothing, which can afford us a just and consistent idea of body.

11. It was claimed in Part II, Section 4 that properly speaking, solidity or impenetrability is nothing but an impossibility of annihilation. [If one body lacked solidity, and its place could be penetrated by another, then the result would be that one of the bodies is annihilated, or ceases to exist altogether. As the author puts it in Part II, Section 4, Before the approach we have the idea of two bodies. After it we have the idea only of one. ’Tis impossible for the mind to preserve any notion of difference betwixt two bodies of the same nature existing in the same place at the same time. If a body has solidity, its place cannot be penetrated by another, in which case there cannot be annihilation of either of the bodies.] If we are to understand the notion of solidity in these terms, we must have some conception of what it is that cannot be annihilated. An impossibility of being annihilated cannot exist, and can never be conceiv’d to exist, by itself; but necessarily requires some object or real existence, to which it may belong. But if we do not have use of the secondary qualities to conceptualize the object, it is hard to see how we could do so, given that neither motion, figure, extension, nor solidity—the principal relevant primary qualities, is available.

12. Another principle which must not be overlooked is that all ideas are copies of impressions. [See Part I, Section 1 for this principle and its defense.] The impressions of vision, hearing, smell, taste, “are affirm’d by modern philosophers to be without any resembling objects.” [Locke allows that hearing, smell and taste produce ideas only of secondary qualities. But he did regard vision as producing ideas of primary qualities: sight [is] the most comprehensive of all our senses, conveying to our minds the ideas of light and colours, which are peculiar only to that sense; and also the far different ideas of space, figure, and motion (Essay, Book II, Chapter IX, Section 9. Berkeley argued in the New Theory of Vision, Section CXXX, that only light and colors, both secondary qualities, are perceived by sight.] Because solidity is supposed to be a primary quality, it cannot be derived from any of those sense-modalities. So touch or feeling is the only remaining sense that could produce an impression that is the origin of our idea of solidity. The author allows that we naturally imagine, that we feel the solidity of bodies, and need but touch any object in order to perceive this quality. [Locke put it his way in Section 8 of Book II of the Essay, If any one ask me, What this solidity is, I send him to his senses to inform him. Let him put a flint or a football between his hands, and then endeavour to join them, and he will know.] The author regards this way of thinking as more popular than philosophical, a claim he will try to justify in the next two paragraphs.

13. The first point is that bodies are felt by means of their solidity, but the feeling is not the same as the solidity, and the feeling and the solidity do not resemble each other. Someone who cannot feel a table with one hand because he has the palsy in it, “has as perfect an idea of impenetrability, when he observes that hand to be supported by the table, as when he feels the same table with the other hand.” The felt sensation is conveyed by the mind by a motion given to the nerves and animal spirits by the resistance of the object. But the individual links of this chain need not the resemble one another.

14. The second point regards the simplicity of feelings, or sensations, of touch. While the feeling of an extended thing is complex, the feeling of a tangible point must be simple. [And as was argued in Part II, Section 3, there must be simple visible and tangible points if there is to be extension at all.] The feeling of an extended thing is not relevant here, since we are trying to understand solidity independently of extension in order to understand our idea of extension. The author infers from the simplicity of the sensations of touch that they neither represent solidity, or any real object. He produces a thought-experiment to make his point. Consider the difference between a person’s touching a stone and another stone touching it. In both cases there is solidity, but in the former case, there is also a feeling or sensation. To make the cases alike, it would be necessary to remove at least some part of the impression produced by the contact of the hand with the stone. But since the impression is simple, the whole impression would have to be removed. Since the whole impression would have to be removed to make the two cases alike, this “proves that this whole impression has no archetype or model in external objects.” [It is not clear how this conclusion follows from what has been stated. The difference in the two cases is the existence of an impression in one and not the other. To make the two alike, the impression (whether simple or not) would have to be removed. However, this does not seem to prevent there being a resemblance between the impression and the solidity in the object.] A further consideration is that contiguity and impulse add a measure of complexity to the idea of solidity, unlike the simplicity of the feeling. Yet further, the impressions of touch are variable while the solidity that they allegedly represent remains the same, “which is a clear proof that the latter are not representations of the former.”

15. The Section ends with an assessment by the author of the upshot of the criticism of the modern system of philosophy. Reason, or more precisely, the conclusions we form on the basis of cause and effect, tells us that neither colour, sound, taste, nor smell have a continu’d and independent existence. But the arguments of the present Section have shown that without these qualities, nothing has a continued and independent existence [since objects would be bereft of the qualities of motion, figure, extension, and solidity without them]. These conclusions are in a direct and total opposition to the evidence of the senses, which persuades us that bodies have a continued and independent existence.

The Enquiry

The topic of this Section is dealt with briefly in the penultimate paragraph of Part I of the concluding Section 12 of the Enquiry. Hume has there concluded his discussion of a train of skeptical argument against there being a rational basis of the faith we have in our senses. [That argument is described in the notes to Section 2 of Part IV.] He then considers a similar skeptical argument, of a like nature, derived from the most profound philosophy. The examination of this argument could go deeper than what is presented here, but because this kind of argument can so little serve to any serious purpose, the description of it will be brief. Hume recounts the distinction between primary and secondary qualities, which is universally allowed by modern enquirers. Secondary qualities such as colors and tastes are said to be perceptions of the mind which do not exist in external objects or have any resemblance to anything in those objects. [Primary qualities, such as extension and solidity, are said to exist in objects external to our minds and, and our perceptions of them are said to resemble those qualities.] Hume asserts that the account of secondary qualities must apply to the primary qualities as well. The idea of extension is wholly dependent on the sensible ideas or the ideas of secondary qualities. The reason is that the idea of extension is acquired by sight and touch. Given that all visual and tactile qualities are perceptions of the mind, extension must be a perception in the mind as well. One might object that the idea of extension can be abstracted from the sensible ideas. Hume replies that such an abstraction is, upon accurate examination, found to be unintelligible, and even absurd. To perform the abstraction, we would need to separate the extension from its color or from feelings of hardness or softness, but this is inconceivable. Hume compares this fruitless endeavor to that of conceiving a triangle that is neither Isosceles nor Scalenum, nor has any particular length or proportion of sides. The impossibility of doing this leads us to recognize the absurdity of all the scholastic notions with regard to abstraction and general ideas. In a footnote, Hume credits Berkeley for this argument, and he notes that most of the writings of this ingenious author form the best lessons of scepticism, which are to be found either among the ancient or modern philosophers, Bayle not excepted. Berkeley intended to be arguing against skeptics, but in the end his arguments were skeptical only, because they admit of no answer and produce no conviction. The only results of his arguments are to cause that momentary amazement and irresolution and confusion, which are the result of scepticism.

[ Previous Section | Next Section | Treatise Contents | Text of the Treatise ]