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Locke's Essay Book II, Chapter VIII, Sections 7-26.
Locke articulated and defended a distinction between 'primary' and 'secondary' qualities.
"Qualities thus considered in bodies are:
First, such as are utterly inseparable from the body ...[namely] solidity, extension,
figure, and mobility ...
Secondly, such qualities which in truth are nothing in the objects themselves
but powers to produce various sensations in us by their primary qualities, ie
by their bulk, figure, texture, and motion of their insensible parts, as colours,
sounds, tastes, etc. These I call secondary qualities."
An Essay concerning human Understanding, Bk
II, Ch. VIII, Section 9.
Notice that ideas are to be distinguished from qualities. A quality is a power. It is the power a thing has to give rise to an idea in our mind.
There are according to Locke two sorts of qualities: primary and secondary.
A primary quality gives rise to an idea which resembles it. Secondary qualities give rise to ideas, but the ideas are not 'like' the qualities that give rise to them.
Eg taste is produced by the shape and size of the particles of which the substance was made.
Compare that to the idea we have of motion: the moving body has a property which is 'like' the idea it gives rise to.
Thus one attempt to distinguish two sorts of qualities is this:
A secondary quality is a quality which gives rise to an idea which does not resemble it.
Some examples?:
PRIMARY |
SECONDARY |
motion |
smell |
shape |
roughness |
extension |
shininess |
mass |
sound |
Locke says that primary qualities are really 'in' the bodies that have them, whereas secondary qualities are not.
'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 porphyry 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.'
We can imagine a black dog turning grey, but not losing its extension.
A piece of paper can lack smell but not size.
'The ideas of the primary alone 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 ears 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.'
'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.' Essay, Bk II, Ch. VIII, Section 21
'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?' Essay, Bk II, Ch. VIII, Section 20
(Descartes had argued (among other things): Secondary qualities are only perceptible through a single sense.
Malebranche had argued: the perception of secondary qualities varied with the position of the observer, and so cannot be 'in' the object. E.g. a thing appears to have a different colour depending on the angle of perception, or the light.)
Corpuscularianism: You can understand how big things like tables can be thought of as made up of many smaller things grouped together.
But a second thesis is that some of the properties of the big things are to be explained in terms of a simpler set of properties of the elementary things.
and :
"[D]ivision ... can never take away either solidity, extension, figure,
and mobility."
Essay,
Bk II, Ch. VIII, Section 9.
