Primary and secondary qualities Michael Lacewing enquiries@alevelphilosophy.co.uk © Michael Lacewing

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

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

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

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

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

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

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

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