When we experience the world, Locke thinks, our ideas are caused by features in the things we experience. We perceive some of those features as they are, these features are “bulk, figure, texture, or motion”. Locke calls these features of objects ‘primary qualities’. Other features are perceived in ways that are unique to our species. Colour is like that. We perceive colour differently from a deer, and differently again from an eagle. What is going on is that the coloured body’s primary qualities (in this case its surface texture) interacts differently with our different senses: one way with your senses, another with the eagle’s, another with the deer’s. Locke calls these qualities in bodies ‘secondary qualities’. The ideas that we get of these secondary qualities do not resemble the objects. There is no real colour in things.
We also saw some ways in which Locke’s theory of ideas works. We saw that memory is the process of retrieving ideas. Abstraction is the process of discarding all that is not specific about an idea.