1. Primary and secondary qualities
Michael Lacewing
© Michael Lacewing

2. Primary qualities
A ‘quality’ is a ‘power’ a physical object has ‘to produce an idea in our mind’
A snowball produces in us the ideas of ‘white’, ‘cold’ and ‘round’.
Primary qualities are ‘utterly inseparable’ from the object
It has them whatever changes it goes through, even if it is divided into smaller and smaller pieces
The object has these properties ‘in and of itself’
Locke: extension (size), shape, motion, number and solidity.
© Michael Lacewing

3. Solidity
‘Solidity’ doesn’t contrast with being liquid or gas, but is the quality of a physical object whereby it takes up space and excludes other physical objects from occupying exactly the same space.
© Michael Lacewing

4. Secondary qualities
Secondary qualities: qualities that are ‘nothing but powers to produce various sensations in us’
Colours, sounds, tastes, smells, temperature.
By definition, colour is something that is experienced in vision
It is a quality that an object can have only in relation to its being seen by someone. (Likewise for other secondary qualities.)
By contrast, primary qualities are properties of an object that are not related by definition to perceivers.
© Michael Lacewing

5. Locke’s primary qualities
Physical objects must always have some size and shape, they must always be at rest or in motion of some kind, they can be counted
They don’t always have colour or smell, e.g. glass.
But physics suggests physical objects don’t retain all of Locke’s properties, and adds others that aren’t related to being perceived
Electrical charge
Matter/energy transformations.
© Michael Lacewing

6. Are secondary qualities mind-dependent?
Locke first defines secondary qualities as relational properties of physical objects
A power to produce certain sensations when perceived
The power results from the object’s atomic and molecular structure (colour, smell).
Locke also says that secondary qualities don’t ‘really exist in’ physical objects
Without being perceived they ‘vanish and cease, and are reduced to their causes’
A red and white stone in darkness, loses its colour.
© Michael Lacewing

7. Are secondary qualities mind-dependent?
Locke’s second account confuses qualities and ideas:
Qualities are powers in the object, and the causes of ideas
Ideas are the effects of these powers on our minds.
Is colour an idea, a type of sensation we experience, or is it a quality, the property of an object to cause this type of sensation?
If the latter, the stone does not lose its colour in the dark.
© Michael Lacewing

8. Perceptual variation
Put one warm hand and one cold hand in a bowl of tepid water. The water will feel hot to the cold hand, and cold to the hot hand.
The object can’t have two temperatures
So temperature is subjective.
Perceptual variation shows that secondary qualities are mind-dependent.
© Michael Lacewing

9. Direct v. indirect realism
Indirect realism: secondary qualities are mind-dependent, which shows that we don’t perceive physical objects directly
The physical world contains primary qualities only.
Direct realism: secondary qualities are relational properties of physical objects
Science explains what it is for something to be coloured, but colours are no less real than primary qualities.
Indirect realism: no, science explains what it is for us to perceive these properties
A blind man can understand the physics, but not what colour is – because colour is the experience of colour.
© Michael Lacewing