Primary and Secondary Qualities

This topic is concerned with the properties that objects appear to have. The question is whether they are really properties of the objects, or whether some are actually properties of us that we project onto the objects.

Argument for a Distinction

Sharp objects are painful if you touch them. However, we do not think that 'painful' is a property of the object. Why, then, should all the other sensations that arise in us when we interact with objects be properties of the objects?

The Nature of the Distinction

Galileo: Primary qualities are properties of the objects. Secondary qualities are purely in us, and nothing to do with the object at all.

Locke: Primary qualities are those properties of the object that cause a sensation in us which resembles the property in the object. Secondary qualities are those properties that cause a sensation in us which does not resemble the property in the object.

Drawing the Line

Which properties are primary, and which secondary? There are a few ways to draw the line.

• Properties which would exist even if the object were always unobserved are primary.
• Properties which would exist even if the object were the only thing in the universe are primary.
• Properties, like shape, which we can detect with two or more senses are primary.
• If we could be completely mistaken about a property and still function, that property is secondary.

Shape, number, and motion are generally thought of as primary qualities. Colour, odour, and taste are generally thought of as secondary.

Possible Objections

The two accounts of the nature of the distinction are different, so you could criticise either or both.

All of the ways to draw the line are different. You might be able to criticise them for being the wrong sort of distinction, or for classifying properties wrongly, or for making all properties either primary or secondary.

You might also think that you shouldn't draw the distinction at all.