An Essay Concerning Human Understanding / Ein Versuch über den menschlichen Verstand. Auswahlausgabe. John Locke
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§ 19. Let us consider the red and white colours in Porphyre: Hinder light but 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 Porphyre, by the presence or absence of Light; and that those Ideas of whiteness and redness, are really in Porphyre in the light, when ’tis 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.
§ 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 any Body, but an Alteration of the Texture of it?
[146]§ 21. 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 Sensation 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.
§ 22. I have in what just goes before, been engaged in Physical Enquiries a little farther 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 [148]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 Enquiry, 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 also may come to know what Ideas are, and what are not Resemblances of something really existing in the Bodies, we denominate from them.
§ 23. The Qualities then that are in Bodies rightly considered, are of Three sorts.
First, the Bulk, Figure, Number, Situation, and Motion, or Rest of their solid Parts; those are in them, whether we perceive them or no; 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 it self, as is plain in artificial things. These I call 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, Tasts, etc. These are usually called sensible Qualities.
[150]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. These are usually called Powers.
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 no: and upon their different Modifications it is, that the secondary Qualities depend. […]
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§ 26. 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.
Of Perception
§ 1. PERCEPTION, as it is the first faculty of the Mind, exercised about our Ideas; so it is the first and simplest Idea we have from Reflection, and is by some called Thinking in general. Though Thinking, in the propriety of the English Tongue, signifies that sort of operation of the Mind about its Ideas, wherein the Mind is active; where it with some degree of voluntary attention, considers any thing. For in bare naked Perception, the Mind is, for the most part, only passive; and what it perceives, it cannot avoid perceiving.
§ 2. What Perception is, every one will know better by reflecting on what he does himself, when he sees, hears, feels, etc. or thinks, than by any discourse of mine. Whoever reflects on what passes in his own Mind, cannot miss it: And if he does not reflect, all the Words in the World, cannot make him have any notion of it.
§ 3. This is certain, That whatever alterations are made in the Body, if they reach not the Mind; whatever impressions are made on the outward parts, if they are not taken notice of within, there is no Perception. Fire may burn our Bodies, with no other effect, than it does a Billet, unless the motion be continued to the Brain, and there the sence of Heat, or Idea of Pain, be produced in the Mind, wherein consists actual Perception.
§ 4. How often may a Man observe in himself, that whilst his Mind is intently employ’d in the contemplation of some [154]Objects; and curiously surveying some Ideas that are there, it takes no notice of impressions of sounding Bodies, made upon the Organ of Hearing, with the same alteration, that uses to be for the producing the Idea of a Sound? A sufficient impulse there may be on the Organ; but it not reaching the observation of the Mind, there follows no perception: And though the motion, that uses to produce the Idea of sound, be made in the Ear, yet no sound is heard. Want of Sensation in this case, is not through any defect in the Organ, or that the Man’s Ears are less affected, than at other times, when he does hear: