Further Thoughts on Our Simple Ideas from Sensation

1. Positive Ideas from privative causes.

1. Positive ideas caused by the absence of something.

Concerning the simple ideas of Sensation; it is to be considered,—that whatsoever is so constituted in nature as to be able, by affecting our senses, to cause any perception in the mind, doth thereby produce in the understanding a simple idea; which, whatever be the external cause of it, when it comes to be taken notice of by our discerning faculty, it is by the mind looked on and considered there to be a real positive idea in the understanding, as much as any other whatsoever; though, perhaps, the cause of it be but a privation of the subject.

Consider the simple ideas of sensation. Anything in nature capable of causing a perception in the mind by affecting our senses produces a simple idea. Whatever the external cause, once our power of discernment notices the idea, the mind regards the idea as real and positive. The idea is as real and positive as any other idea in the understanding. Yet perhaps the cause is merely the absence of something in the object.

2. Ideas in the mind distinguished from that in things which gives rise to them.

2. Ideas in the mind are distinct from whatever gives rise to those ideas in things.

Thus the ideas of heat and cold, light and darkness, white and black, motion and rest, are equally clear and positive ideas in the mind; though, perhaps, some of the causes which produce them are barely privations, in those subjects from whence our senses derive those ideas. These the understanding, in its view of them, considers all as distinct positive ideas, without taking notice of the causes that produce them: which is an inquiry not belonging to the idea, as it is in the understanding, but to the nature of the things existing without us. These are two very different things, and carefully to be distinguished; it being one thing to perceive and know the idea of white or black, and quite another to examine what kind of particles they must be, and how ranged in the superficies, to make any object appear white or black.

Thus, the ideas of heat and cold, light and darkness, white and black, motion and rest are equally clear. All are positive ideas in the mind. Yet perhaps some causes of these ideas are merely absences in the objects from which our senses receive these ideas. The mind considers all these ideas distinct and positive, without considering their causes. Investigating those causes concerns not the ideas as they exist in the mind, but the nature of things outside us. These are two very different matters, and we must carefully distinguish between them. Perceiving and knowing the idea of white or black is one thing. Examining what kinds of particles, arranged in what ways on an object's surface, make that object appear white or black is quite another.

3. We may have the ideas when we are ignorant of their physical causes.

3. We may have ideas even when we do not know their physical causes.

A painter or dyer who never inquired into their causes hath the ideas of white and black, and other colours, as clearly, perfectly, and distinctly in his understanding, and perhaps more distinctly, than the philosopher who hath busied himself in considering their natures, and thinks he knows how far either of them is, in its cause, positive or privative; and the idea of black is no less positive in his mind than that of white, however the cause of that colour in the external object may be only a privation.

A painter or dyer may never have investigated the causes of white, black, or other colours. Yet such a person’s ideas of these colours are as clear, complete, and distinct as a philosopher’s, perhaps more distinct. The philosopher has studied the nature of these colours. He thinks he knows how far each colour’s cause is something present or merely something absent. And the painter’s or dyer’s idea of black is no less a definite idea than the idea of white. This is so even if black in an external object may be caused only by something’s absence.

4. Why a privative cause in nature may occasion a positive idea.

4. Why the absence of something in nature may give rise to a positive idea.

If it were the design of my present undertaking to inquire into the natural causes and manner of perception, I should offer this as a reason why a privative cause might, in some cases at least, produce a positive idea; viz. that all sensation being produced in us only by different degrees and modes of motion in our animal spirits, variously agitated by external objects, the abatement of any former motion must as necessarily produce a new sensation as the variation or increase of it; and so introduce a new idea, which depends only on a different motion of the animal spirits in that organ.

If my present purpose were to investigate the natural causes of perception and how perception works, I would offer this explanation. A cause involving an absence might, at least in some cases, produce a positive idea for the following reason. All sensation arises in us only from different degrees and kinds of motion in our animal spirits. External objects set these spirits moving in different ways. So a decrease in an existing motion must produce a new sensation just as necessarily as a change or increase. That new sensation would then introduce a new idea. The new idea depends only on a different motion of the animal spirits in the organ involved.

5. Negative names need not be meaningless.

5. Negative terms do not have to be meaningless.

But whether this be so or not I will not here determine, but appeal to every one’s own experience, whether the shadow of a man, though it consists of nothing but the absence of light (and the more the absence of light is, the more discernible is the shadow) does not, when a man looks on it, cause as clear and positive idea in his mind, as a man himself, though covered over with clear sunshine? And the picture of a shadow is a positive thing. Indeed, we have negative names, to which there be no positive ideas; but they consist wholly in negation of some certain ideas, as SILENCE, INVISIBLE; but these signify not any ideas in the mind but their absence.

But I will not decide here whether this is so. Instead, I ask everyone to consider their own experience. A man’s shadow consists only of the absence of light. (The greater the absence of light, the clearer the shadow.) Yet doesn’t looking at the shadow produce an idea as clear and positive as looking at the man in full sunshine? And a picture of a shadow is a positive thing. We do have negative names that correspond to no positive ideas. But these names express only the absence of certain ideas, as with SILENCE and INVISIBLE. These words do not signify ideas in the mind, but the absence of those ideas.

6. Whether any ideas are due to causes really private.

6. Whether any ideas come from truly private causes.

And thus one may truly be said to see darkness. For, supposing a hole perfectly dark, from whence no light is reflected, it is certain one may see the figure of it, or it may be painted; or whether the ink I write with makes any other idea, is a question. The privative causes I have here assigned of positive ideas are according to the common opinion; but, in truth, it will be hard to determine whether there be really any ideas from a privative cause, till it be determined, whether rest be any more a privation than motion.

And so someone may truly be said to see darkness. Suppose a hole is completely dark and reflects no light. We can certainly see its shape, or paint it. Whether the ink I write with produces any different idea is a question. In identifying absences as causes of positive ideas, I have followed the common view. But in truth, it will be hard to determine whether any ideas really arise from an absence. First, we must determine whether rest is any more an absence than motion is.

7. Ideas in the Mind, Qualities in Bodies.

7. Ideas in the Mind, Qualities in Physical Objects.

To discover the nature of our IDEAS the better, and to discourse of them intelligibly, it will be convenient to distinguish them AS THEY ARE IDEAS OR PERCEPTIONS IN OUR MINDS; and AS THEY ARE MODIFICATIONS OF MATTER IN THE BODIES THAT CAUSE SUCH PERCEPTIONS IN US: that so we may not think (as perhaps usually is done) that they are exactly the images and resemblances of something inherent in the subject; most of those of sensation being in the mind no more the likeness of something existing without us, than the names that stand for them are the likeness of our ideas, which yet upon hearing they are apt to excite in us.

To better understand the nature of our IDEAS and discuss them clearly, we should distinguish between two aspects of them. First, AS IDEAS OR PERCEPTIONS IN OUR MINDS. Second, AS PHYSICAL FEATURES OF THE BODIES THAT CAUSE THESE PERCEPTIONS IN US. This distinction may prevent us from thinking that our ideas exactly resemble something inherent in the objects themselves. Perhaps we usually make this mistake. Most ideas produced by sensation resemble nothing outside us any more than names resemble the ideas they represent. Yet hearing those names tends to bring those ideas to mind.

8. Our Ideas and the Qualities of Bodies.

8. Our Ideas and the Properties of Physical Objects.

Whatsoever the mind perceives IN ITSELF, or is the immediate object of perception, thought, or understanding, that I call IDEA; and the power to produce any idea in our mind, I call QUALITY of the subject wherein that power is. Thus a snowball having the power to produce in us the ideas of white, cold, and round,—the power to produce those ideas in us, as they are in the snowball, I call qualities; and as they are sensations or perceptions in our understandings, I call them ideas; which IDEAS, if I speak of sometimes as in the things themselves, I would be understood to mean those qualities in the objects which produce them in us.

Whatever the mind perceives within itself, I call an IDEA. This includes any immediate object of perception, thought, or understanding. The power of something to produce an idea in our mind, I call a QUALITY of that thing. For example, a snowball has the power to produce in us the ideas of white, cold, and round. I call the powers in the snowball that produce these ideas qualities. I call the resulting sensations or perceptions in our minds ideas. If I sometimes speak of these IDEAS as being in things themselves, I mean the qualities in those objects. These qualities produce the ideas in us.

9. Primary Qualities of Bodies.

9. Primary Qualities of Physical Objects.

Concerning these qualities, we, I think, observe these primary ones in bodies that produce simple ideas in us, viz. SOLIDITY, EXTENSION, MOTION or REST, NUMBER or FIGURE. These, which I call ORIGINAL or PRIMARY qualities of body, are wholly inseparable from it; 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: v.g. Take a grain of wheat, divide it into two parts; each part has still solidity, extension, figure, and mobility: divide it again, and it retains still the same qualities; and so divide it on, till the parts become insensible; they must retain still each of them all those qualities. For division (which is all that a mill, or pestle, or any other body, does upon another, in reducing it to insensible parts) can never take away either solidity, extension, figure, or mobility from any body, but only makes two or more distinct separate masses of matter, of that which was but one before; all which distinct masses, reckoned as so many distinct bodies, after division, make a certain number.

Among these qualities, I think we observe these primary ones in bodies that produce simple ideas in us: SOLIDITY, EXTENSION, MOTION or REST, NUMBER or FIGURE. I call these the ORIGINAL or PRIMARY qualities of a body. They are entirely inseparable from the body. The body always keeps these qualities through every alteration and change, whatever force is applied to it. Our senses always find these qualities in every particle of matter large enough to be perceived. The mind also finds these qualities inseparable from every particle, even those too small for our senses to perceive individually. For example, take a grain of wheat and divide it into two parts. Each part still has solidity, extension, shape, and the ability to move. Divide the grain again, and each part still retains the same qualities. Continue dividing until the parts become too small to perceive. Each part must still retain all those qualities. For division can never remove solidity, extension, shape, or the ability to move from any body. Division is all that a mill, pestle, or any other body does to another when reducing it to imperceptible parts. Division only turns what was one mass of matter into two or more distinct, separate masses. After division, these separate masses, counted as distinct bodies, make up a definite number.

10. [not in early editions]

10. [not included in early editions]

11. How Bodies produce Ideas in us.

11. How physical objects produce ideas in us.

The next thing to be considered is, how bodies operate one upon another; and that is manifestly by impulse, and nothing else. It being impossible to conceive that body should operate on WHAT IT DOES NOT TOUCH (which is all one as to imagine it can operate where it is not), or when it does touch, operate any other way than by motion.

The next question is how bodies act on one another. Clearly, they do so by impact and nothing else. For it is impossible to imagine a body acting on WHAT IT DOES NOT TOUCH. That would be the same as imagining a body acting where it is not present. And when bodies do touch, it is impossible to imagine them acting on one another in any way except through motion.

12. By motions, external, and in our organism.

12. Through movements outside us and within our bodies.

If then external objects be not united to our minds when they produce ideas therein; and yet we perceive these ORIGINAL qualities in such of them as singly fall under our senses, it is evident that some motion must be thence continued by our nerves, or animal spirits, by some parts of our bodies, to the brains or the seat of sensation, there to produce in our minds the particular ideas we have of them. And since the extension, figure, number, and motion of bodies of an observable bigness, may be perceived at a distance by the sight, it is evident some singly imperceptible bodies must come from them; to the eyes, and thereby convey to the brain some motion; which produces these ideas which we have of them in us.

Suppose, then, that external objects are not united with our minds when they produce ideas in our minds. Yet we perceive these ORIGINAL qualities in individual objects that our senses can detect. If so, some motion must clearly travel from those objects through our nerves, animal spirits, or other bodily parts. That motion must reach the brain, or the seat of sensation, to produce our particular ideas of those objects. And we can see the size, shape, number, and motion of bodies large enough to observe, even at a distance. Since we can perceive these qualities from a distance, some bodies too small to perceive individually must clearly reach our eyes. These tiny bodies must come from the bodies we see and transmit some motion to the brain through the eyes. That motion produces in us the ideas we have of the bodies we see.

13. How secondary Qualities produce their ideas.

13. How secondary qualities produce ideas in us.

After the same manner that the ideas of these original qualities are produced in us, we may conceive that the ideas of SECONDARY qualities are also produced, viz. by the operation of insensible particles on our senses. For, it being manifest that there are bodies and good store of bodies, each whereof are so small, that we cannot by any of our senses discover either their bulk, figure, or motion,—as is evident in the particles of the air and water, and others extremely smaller than those; perhaps as much smaller than the particles of air and water, as the particles of air and water are smaller than peas or hail-stones;—let us suppose at present that, the different motions and figures, bulk and number, of such particles, affecting the several organs of our senses, produce in us those different sensations which we have from the colours and smells of bodies; v.g. that a violet, by the impulse of such insensible particles of matter, of peculiar figures and bulks, and in different degrees and modifications of their motions, causes the ideas of the blue colour, and sweet scent of that flower to be produced in our minds. It being no more impossible to conceive that God should annex such ideas to such motions, with which they have no similitude, than that he should annex the idea of pain to the motion of a piece of steel dividing our flesh, with which that idea hath no resemblance.

We may understand how ideas of SECONDARY qualities arise in the same way as ideas of these original qualities. Both arise through the action of particles too small for our senses to detect. Clearly, there are many bodies so small that none of our senses can detect their size, shape, or motion. The particles of air and water show this, as do other particles far smaller than those. Perhaps these other particles are smaller by as much as air and water particles are smaller than peas or hailstones. For now, let us suppose that such particles act on our various sense organs through differences in motion, shape, size, and number. Let us suppose these differences produce the different sensations we receive from the colours and smells of bodies. For example, a violet sends out tiny particles of matter that strike our senses. These particles have particular shapes and sizes, and their movements differ in degree and kind. Through these particles, the violet produces in our minds the ideas of its blue colour and sweet scent. We can conceive of God linking such ideas to such movements, even though the ideas bear no resemblance to the movements. This is no harder to conceive than God linking the idea of pain to a steel blade moving through our flesh. The idea of pain bears no resemblance to that movement either.

14. They depend on the primary Qualities.

14. They depend on the primary qualities.

What I have said concerning colours and smells may be understood also of tastes and sounds, and other the like sensible qualities; which, whatever reality we by mistake attribute to them, are in truth nothing in the objects themselves, but powers to produce various sensations in us; and depend on those primary qualities, viz. bulk, figure, texture, and motion of parts and therefore I call them SECONDARY QUALITIES.

What I have said about colours and smells also applies to tastes, sounds, and other similar qualities we sense. Whatever reality we mistakenly attribute to these qualities, they are only powers in objects to produce various sensations in us. These powers depend on the primary qualities of the objects' parts: size, shape, arrangement, and motion. For this reason, I call them SECONDARY QUALITIES.

15. Ideas of primary Qualities are Resemblances; of secondary, not.

15. Ideas of primary qualities resemble those qualities, but ideas of secondary qualities do not.

From whence I think it easy to draw this observation,—that the ideas of primary qualities of bodies are resemblances of them, and their patterns do really exist in the bodies themselves, but the ideas produced in us by these secondary qualities have no resemblance of them at all. There is nothing like our ideas, existing in the bodies themselves. They are, in the bodies we denominate from them, only a power to produce those sensations in us: and what is sweet, blue, or warm in idea, is but the certain bulk, figure, and motion of the insensible parts, in the bodies themselves, which we call so.

From this, I think we can easily draw the following conclusion. Our ideas of bodies’ primary qualities resemble those qualities, and the patterns for these ideas really exist in bodies themselves. But the ideas produced in us by secondary qualities do not resemble those qualities at all. Nothing like these ideas exists in the bodies themselves. In the bodies we name after these sensations, secondary qualities are only powers to produce those sensations in us. What we experience as sweet, blue, or warm is, in the bodies themselves, only a particular size, shape, and motion of parts too small to perceive.

16. Examples.

16. Examples.

Flame is denominated hot and light; snow, white and cold; and manna, white and sweet, from the ideas they produce in us. Which qualities are commonly thought to be the same in those bodies that those ideas are in us, the one the perfect resemblance of the other, as they are in a mirror, and it would by most men be judged very extravagant if one should say otherwise. And yet he that will consider that the same fire that, at one distance produces in us the sensation of warmth, does, at a nearer approach, produce in us the far different sensation of pain, ought to bethink himself what reason he has to say—that this idea of warmth, which was produced in him by the fire, is ACTUALLY IN THE FIRE; and his idea of pain, which the same fire produced in him the same way, is NOT in the fire. Why are whiteness and coldness in snow, and pain not, when it produces the one and the other idea in us; and can do neither, but by the bulk, figure, number, and motion of its solid parts?

We call flame hot and bright, snow white and cold, and manna white and sweet, because of the ideas they produce in us. People commonly think these qualities in objects are just like the ideas in our minds. They think one perfectly resembles the other, as in a mirror. Most people would think anyone who said otherwise was being very unreasonable. Yet consider how the same fire produces a sensation of warmth at one distance and a very different sensation, pain, closer up. Anyone who considers this should ask what reason there is for the following distinction. Why say the idea of warmth produced by the fire is ACTUALLY IN THE FIRE? And why say the idea of pain, produced by the same fire in the same way, is NOT in the fire? Why are whiteness and coldness in snow, but pain is not, when snow produces all these ideas in us? Snow can produce these ideas only through the size, shape, number, and motion of its solid parts.

17. The ideas of the Primary alone really exist.

17. Only ideas of primary qualities really exist.

The particular bulk, number, figure, and motion of the parts of fire or snow are really in them,—whether any one’s senses perceive them or no: and therefore they may be called REAL qualities, because they really exist in those bodies. But light, heat, whiteness, or coldness, are no more really in them than sickness or pain is in manna. Take away the sensation of them; let not the eyes see light or colours, nor the ear hear sounds; let the palate not taste, nor the nose smell, and all colours, tastes, odours, and sounds, AS THEY ARE SUCH PARTICULAR IDEAS, vanish and cease, and are reduced to their causes, i.e. bulk, figure, and motion of parts.

The size, number, shape, and motion of the particles in fire or snow really exist in those substances. These qualities exist whether anyone senses them or not. So they may be called REAL qualities, because they really exist in those bodies. But light, heat, whiteness, and coldness are no more really in fire or snow than sickness or pain is in manna. Remove the sensations of these qualities. Let the eyes see no light or colours, and the ears hear no sounds. Let the tongue taste nothing, and the nose smell nothing. Then all colours, tastes, smells, and sounds, AS THEY ARE SUCH PARTICULAR IDEAS, vanish and cease to exist. All that remains is their causes: the size, shape, and motion of particles.

18. The secondary exist in things only as modes of the primary.

18. Secondary qualities exist in things only as forms of their primary qualities.

A piece of manna of a sensible bulk is able to produce in us the idea of a round or square figure; and by being removed from one place to another, the idea of motion. This idea of motion represents it as it really is in manna moving: a circle or square are the same, whether in idea or existence, in the mind or in the manna. And this, both motion and as figure, are really in the manna, whether we take notice of primary, them or no: this everybody is ready to agree to. Besides, manna, by the bulk, figure, texture, and motion of its parts, has a power to produce the sensations of sickness, and sometimes of acute pains or gripings in us. That these ideas of sickness and pain are NOT in the manna, but effects of its operations on us, and are nowhere when we feel them not; this also every one readily agrees to. And yet men are hardly to be brought to think that sweetness and whiteness are not really in manna; which are but the effects of the operations of manna, by the motion, size, and figure of its particles, on the eyes and palate: as the pain and sickness caused by manna are confessedly nothing but the effects of its operations on the stomach and guts, by the size, motion, and figure of its insensible parts, (for by nothing else can a body operate, as has been proved): as if it could not operate on the eyes and palate, and thereby produce in the mind particular distinct ideas, which in itself it has not, as well as we allow it can operate on the guts and stomach, and thereby produce distinct ideas, which in itself it has not. These ideas, being all effects of the operations of manna on several parts of our bodies, by the size, figure, number, and motion of its parts;—why those produced by the eyes and palate should rather be thought to be really in the manna, than those produced by the stomach and guts; or why the pain and sickness, ideas that are the effect of manna, should be thought to be nowhere when they are not felt; and yet the sweetness and whiteness, effects of the same manna on other parts of the body, by ways equally as unknown, should be thought to exist in the manna, when they are not seen or tasted, would need some reason to explain.

A piece of manna large enough to perceive can give us the idea of a round or square shape. Moving the manna from one place to another can give us the idea of motion. This idea represents motion as it really occurs in the moving manna. A circle or square is the same whether it exists as an idea in the mind or in the manna. Both motion and shape are really in the manna, whether we notice these primary qualities or not. Everyone readily agrees to this. Besides, manna can make us feel sick and sometimes cause sharp pains or cramps. Manna has this power because of the size, shape, arrangement, and motion of its parts. Everyone also readily agrees that these ideas of sickness and pain are NOT in the manna. Instead, these sensations result from manna acting on us, and exist nowhere when we do not feel them. Yet people can hardly be persuaded that sweetness and whiteness are not really in manna. These sensations are merely effects of manna acting on our eyes and palate through its particles’ motion, size, and shape. Similarly, everyone admits that manna causes pain and sickness merely by acting on the stomach and intestines. Manna acts on these organs through the size, motion, and shape of parts too small to perceive. As has been proved, a body can act only through these properties. People reason as if manna could not act on the eyes and palate to produce particular, distinct ideas it does not itself contain. Yet we allow that manna can act on the intestines and stomach to produce distinct ideas it does not itself contain. All these ideas result from manna acting on different parts of our bodies. Manna produces these effects through the size, shape, number, and motion of its parts. Why, then, should sensations produced through the eyes and palate be considered really present in the manna? Why should we think these sensations are in manna any more than sensations produced through the stomach and intestines? Pain and sickness are ideas caused by manna, yet we consider them to exist nowhere when we do not feel them. Sweetness and whiteness result from the same manna acting on other parts of the body, in ways equally unknown to us. Yet we consider sweetness and whiteness to exist in manna even when no one sees or tastes it. Some reason is needed to explain this distinction.

19. Examples.

19. Examples.

Let us consider the red and white colours in porphyry. Hinder light from striking on it, and its colours vanish; it no longer produces any such ideas in us: upon the return of light it produces these appearances on us again. Can any one think any real alterations are made in the porphyry by the presence or absence of light; and that those ideas of whiteness and redness are really in porphryry in the light, when it is plain IT HAS NO COLOUR IN THE DARK? It has, indeed, such a configuration of particles, both night and day, as are apt, by the rays of light rebounding from some parts of that hard stone, to produce in us the idea of redness, and from others the idea of whiteness; but whiteness or redness are not in it at any time, but such a texture that hath the power to produce such a sensation in us.

Consider the red and white colours in porphyry. Block light from reaching the stone, and its colours vanish. The stone no longer produces any such ideas in us. When light returns, the stone produces these appearances in us again. Can anyone think that the presence or absence of light makes any real changes in the porphyry? Can anyone think that ideas of whiteness and redness really exist in the stone when light strikes it? Yet plainly, THE STONE HAS NO COLOUR IN THE DARK. The stone does have an arrangement of particles, both night and day, capable of producing these ideas in us. Light rays reflected from some parts of the hard stone produce the idea of redness. Rays reflected from other parts produce the idea of whiteness. But neither whiteness nor redness is ever in the stone. The stone has only a structure with the power to produce these sensations in us.

20. Pound an almond, and the clear white colour will be altered into a dirty one, and the sweet taste into an oily one. What real alteration can the beating of the pestle make in an body, but an alteration of the texture of it?

20. Pound an almond, and its pure white colour will turn dirty, and its sweet taste will turn oily. What real change can pounding with a pestle make in a body, except to change its structure?

21. Explains how water felt as cold by one hand may be warm to the other.

21. Explains how water that feels cold to one hand may feel warm to the other.

Ideas being thus distinguished and understood, we may be able to give an account how the same water, at the same time, may produce the idea of cold by one hand and of heat by the other: whereas it is impossible that the same water, if those ideas were really in it, should at the same time be both hot and cold. For, if we imagine WARMTH, as it is in our hands, to be nothing but a certain sort and degree of motion in the minute particles of our nerves or animal spirits, we may understand how it is possible that the same water may, at the same time, produce the sensations of heat in one hand and cold in the other; which yet FIGURE never does, that never producing the idea of a square by one hand which has produced the idea of a globe by another. But if the sensation of heat and cold be nothing but the increase or diminution of the motion of the minute parts of our bodies, caused by the corpuscles of any other body, it is easy to be understood, that if that motion be greater in one hand than in the other; if a body be applied to the two hands, which has in its minute particles a greater motion than in those of one of the hands, and a less than in those of the other, it will increase the motion of the one hand and lessen it in the other; and so cause the different sensations of heat and cold that depend thereon.

With these ideas distinguished and understood, we may explain how the same water can feel cold to one hand and hot to the other. If those ideas were really in the water, the water could not be both hot and cold at once. Suppose WARMTH in our hands is only a certain kind and degree of motion in tiny particles. These particles belong to our nerves or animal spirits. We can then understand how the same water may feel hot to one hand and cold to the other. Yet FIGURE never does anything like this. The same shape never produces the idea of a square through one hand and a globe through the other. But suppose sensations of heat and cold are only increases or decreases in the motion of our bodies’ tiny parts. Suppose these changes are caused by the tiny particles of another body. We can then easily understand how the different sensations arise. Suppose the motion in one hand is greater than in the other. Now suppose an object touches both hands. Its tiny particles move more than those in one hand, but less than those in the other. The object will increase the motion in one hand and reduce the motion in the other. In this way, the object will cause the different sensations of heat and cold that depend on those changes.

22. An excursion into natural philosophy.

22. A digression into the study of nature.

I have in what just goes before been engaged in physical inquiries a little further than perhaps I intended. But, it being necessary to make the nature of sensation a little understood; and to make the difference between the QUALITIES in bodies, and the IDEAS produced by them in the mind, to be distinctly conceived, without which it were impossible to discourse intelligibly of them;—I hope I shall be pardoned this little excursion into natural philosophy; it being necessary in our present inquiry to distinguish the PRIMARY and REAL qualities of bodies, which are always in them (viz. solidity, extension, figure, number, and motion, or rest, and are sometimes perceived by us, viz. when the bodies they are in are big enough singly to be discerned), from those SECONDARY and IMPUTED qualities, which are but the powers of several combinations of those primary ones, when they operate without being distinctly discerned;—whereby we may also come to know what ideas are, and what are not, resemblances of something really existing in the bodies we denominate from them.

In the preceding discussion, I have gone a little further into physical inquiries than perhaps I intended. But I needed to explain something of the nature of sensation. I also needed to clarify the difference between the QUALITIES in bodies and the IDEAS they produce in the mind. Without that distinction, it would be impossible to discuss these matters intelligibly. So I hope I will be forgiven this brief excursion into natural philosophy. Our present inquiry requires us to distinguish the PRIMARY and REAL qualities of bodies from their SECONDARY and IMPUTED qualities. Primary qualities are always present in bodies: solidity, extension, shape, number, and motion or rest. We sometimes perceive these qualities, namely when individual bodies are large enough for us to distinguish them. Secondary qualities are merely powers arising from various combinations of primary qualities, operating without those primary qualities being separately perceived. By making this distinction, we may also learn which ideas resemble something actually existing in bodies, and which do not. These are the bodies we name after those ideas.

23. Three Sorts of Qualities in Bodies.

23. Three Types of Qualities in Physical Objects.

The qualities, then, that are in bodies, rightly considered are of three sorts:—

So, when properly understood, the qualities in physical objects fall into three types:

FIRST, The bulk, figure, number, situation, and motion or rest of their solid parts. Those are in them, whether we perceive them or not; and when they are of that size that we can discover them, we have by these an idea of the thing as it is in itself; as is plain in artificial things. These I call PRIMARY QUALITIES.

FIRST, the size, shape, number, arrangement, and motion or rest of their solid parts. These qualities exist in objects whether we perceive them or not. When the parts are large enough for us to detect, these qualities give us an idea of the object as it really is. This is clear in human-made objects. I call these PRIMARY QUALITIES.

SECONDLY, The power that is in any body, by reason of its insensible primary qualities, to operate after a peculiar manner on any of our senses, and thereby produce in US the different ideas of several colours, sounds, smells, tastes, &c. These are usually called SENSIBLE QUALITIES.

SECONDLY, a body’s power to affect any of our senses in a particular way comes from its imperceptible primary qualities. This power produces in US different ideas of colours, sounds, smells, tastes, and so on. These powers are usually called SENSIBLE QUALITIES.

THIRDLY, The power that is in any body, by reason of the particular constitution of its primary qualities, to make such a change in the bulk, figure, texture, and motion of ANOTHER BODY, as to make it operate on our senses differently from what it did before. Thus the sun has a power to make wax white, and fire to make lead fluid.

THIRDLY, a body has the power to change the size, shape, texture, and motion of ANOTHER BODY. This power comes from the particular arrangement of the first body's primary qualities. Such changes cause the other body to affect our senses differently than before. Thus the sun has the power to make wax white, and fire has the power to make lead liquid.

The first of these, as has been said, I think may be properly called real, original, or primary qualities; because they are in the things themselves, whether they are perceived or not: and upon their different modifications it is that the secondary qualities depend.

As I have said, I think the first of these may properly be called real, original, or primary qualities. This is because these qualities exist in things themselves, whether anyone perceives them or not. And secondary qualities depend on the different forms these primary qualities take.

The other two are only powers to act differently upon other things: which powers result from the different modifications of those primary qualities.

The other two are only powers to act on other things in different ways. These powers result from differences in how those primary qualities are arranged.

24. The first are Resemblances; the second thought to be Resemblances, but are not, the third neither are nor are thought so.

24. The first are resemblances. The second are thought to be resemblances, but are not. The third are neither resemblances nor thought to be resemblances.

But, though the two latter sorts of qualities are powers barely, and nothing but powers, relating to several other bodies, and resulting from the different modifications of the original qualities, yet they are generally otherwise thought of. For the SECOND sort, viz. the powers to produce several ideas in us, by our senses, are looked upon as real qualities in the things thus affecting us: but the THIRD sort are called and esteemed barely powers, v.g. The idea of heat or light, which we receive by our eyes, or touch, from the sun, are commonly thought real qualities existing in the sun, and something more than mere powers in it. But when we consider the sun in reference to wax, which it melts or blanches, we look on the whiteness and softness produced in the wax, not as qualities in the sun, but effects produced by powers in it. Whereas, if rightly considered, these qualities of light and warmth, which are perceptions in me when I am warmed or enlightened by the sun, are no otherwise in the sun, than the changes made in the wax, when it is blanched or melted, are in the sun. They are all of them equally POWERS IN THE SUN, DEPENDING ON ITS PRIMARY QUALITIES; whereby it is able, in the one case, so to alter the bulk, figure, texture, or motion of some of the insensible parts of my eyes or hands, as thereby to produce in me the idea of light or heat; and in the other, it is able so to alter the bulk, figure, texture, or motion of the insensible parts of the wax, as to make them fit to produce in me the distinct ideas of white and fluid.

But the last two kinds of qualities are merely powers, and nothing more. These powers relate to various other bodies and arise from different arrangements of the original qualities. Yet people generally think of these two kinds differently. The SECOND kind consists of powers to produce various ideas in us through our senses. People regard these powers as real qualities in the things affecting us. But the THIRD kind is called and regarded as merely powers. For example, we receive ideas of heat or light from the sun through sight or touch. People commonly think heat and light are real qualities existing in the sun, something more than mere powers. But we think differently when we consider how the sun melts or whitens wax. We regard the whiteness and softness produced in the wax not as qualities in the sun, but as effects of its powers. Yet, properly considered, light and warmth are perceptions in me when the sun lights or warms me. These qualities exist in the sun only as the changes in wax exist there when the sun whitens or melts it. All these are equally POWERS IN THE SUN, DEPENDING ON ITS PRIMARY QUALITIES. In one case, these powers alter the size, shape, texture, or motion of some parts of my eyes or hands. Those parts are too small to perceive, and these changes produce in me the idea of light or heat. In the other case, the sun alters the size, shape, texture, or motion of the wax’s parts, also too small to perceive. These changes make the wax’s parts capable of producing in me the distinct ideas of whiteness and fluidity.

25. Why the secondary are ordinarily taken for real Qualities and not for bare Powers.

25. Why secondary qualities are usually seen as real qualities rather than mere powers.

The reason why the one are ordinarily taken for real qualities, and the other only for bare powers, seems to be because the ideas we have of distinct colours, sounds, &c. containing nothing at all in them of bulk, figure, or motion we are not apt to think them the effects of these primary qualities; which appear not, to our senses, to operate in their production, and with which they have not any apparent congruity or conceivable connexion. Hence it is that we are so forward as to imagine, that those ideas are the resemblances of something really existing in the objects themselves since sensation discovers nothing of bulk, figure, or motion of parts in their production; nor can reason show how bodies BY THEIR BULK, FIGURE, AND MOTION, should produce in the mind the ideas of blue or yellow, &c. But, in the other case in the operations of bodies changing the qualities one of another, we plainly discover that the quality produced hath commonly no resemblance with anything in the thing producing it; wherefore we look on it as a bare effect of power. For, through receiving the idea of heat or light from the sun, we are apt to think IT is a perception and resemblance of such a quality in the sun; yet when we see wax, or a fair face, receive change of colour from the sun, we cannot imagine THAT to be the reception or resemblance of anything in the sun, because we find not those different colours in the sun itself. For, our senses being able to observe a likeness or unlikeness of sensible qualities in two different external objects, we forwardly enough conclude the production of any sensible quality in any subject to be an effect of bare power, and not the communication of any quality which was really in the efficient, when we find no such sensible quality in the thing that produced it. But our senses, not being able to discover any unlikeness between the idea produced in us, and the quality of the object producing it, we are apt to imagine that our ideas are resemblances of something in the objects, and not the effects of certain powers placed in the modification of their primary qualities, with which primary qualities the ideas produced in us have no resemblance.

We usually treat the first kind as real qualities and the second as mere powers. The reason seems to be that our ideas of distinct colours, sounds, and so on contain no size, shape, or motion. So we are not inclined to think these ideas result from those primary qualities. Our senses do not show these primary qualities at work in producing the ideas. Nor do the ideas have any apparent similarity or conceivable connection to those qualities. Because of this, we readily imagine that our ideas resemble something actually existing in the objects themselves. Our senses reveal no size, shape, or movement of parts involved in producing these ideas. Nor can reason explain how bodies, THROUGH THEIR SIZE, SHAPE, AND MOTION, produce ideas of blue, yellow, and so on in the mind. But the situation is different when bodies act on one another and change one another’s qualities. Here we clearly observe that the quality produced commonly resembles nothing in the body producing it. So we regard the new quality as merely the effect of a power. For when we receive an idea of heat or light from the sun, we tend to think of IT as a perception of, and resemblance to, such a quality in the sun. Yet we also see wax or a fair face change colour because of the sun. We cannot imagine THAT change as receiving or resembling anything in the sun. For we do not find those different colours in the sun itself. Our senses can observe similarities or differences between the qualities we perceive in two external objects. So we readily draw a conclusion when something produces a perceptible quality that we cannot find in the producer itself. We conclude that the new quality results merely from a power. We do not think a quality actually present in the cause has been passed on to the object affected. But our senses cannot discover any difference between an idea produced in us and the object’s quality that produces it. So we tend to imagine that our ideas resemble something in the objects. We do not regard these ideas as effects of certain powers arising from the particular arrangements of the objects’ primary qualities. Yet the ideas produced in us bear no resemblance to those primary qualities.

26. Secondary Qualities twofold; first, immediately perceivable; secondly, mediately perceivable.

26. Secondary qualities are of two kinds: first, those perceived directly, and second, those perceived indirectly.

To conclude. Beside those before-mentioned primary qualities in bodies, viz. bulk, figure, extension, number, and motion of their solid parts; all the rest, whereby we take notice of bodies, and distinguish them one from another, are nothing else but several powers in them, depending on those primary qualities; whereby they are fitted, either by immediately operating on our bodies to produce several different ideas in us; or else, by operating on other bodies, so to change their primary qualities as to render them capable of producing ideas in us different from what before they did. The former of these, I think, may be called secondary qualities IMMEDIATELY PERCEIVABLE: the latter, secondary qualities, MEDIATELY PERCEIVABLE.

To conclude, bodies have the primary qualities mentioned earlier: size, shape, extension, number, and the motion of their solid parts. All other qualities by which we notice bodies and distinguish one from another are merely powers in those bodies. These powers depend on the primary qualities and work in either of two ways. Bodies can act directly on our bodies to produce different ideas in us. Or bodies can act on other bodies, changing those other bodies’ primary qualities. These changes enable the affected bodies to produce different ideas in us than before. The first kind, I think, may be called secondary qualities DIRECTLY PERCEIVABLE. The second kind may be called secondary qualities INDIRECTLY PERCEIVABLE.