According to Locke, since we know only our ideas, it is important to understand them well. Some ideas represent things in the world truly or exactly as those things are apart from how we perceive them. Examples of this according to Locke would be an objects solidity, extension, figure, motion, and number. These are the primary qualities of an object. Other ideas occur in our minds as a result of their being caused by primary qualities. Examples of this would be the figure or motion or insensible particles such as atoms or molecules. These ideas are what Locked called secondary qualities. The secondary qualities do not represent thing in the world as they are. They only appear to us in that way (e.g. colors, sounds). As long as we limit claims about the world to ideas of primary qualities we can rely on our experience for knowledge.
Representative Realism is a modification of Common Sense Realism which is a view that assumes that there is a world of physical objects such as houses, trees, cars, goldfish, teaspoons, footballs, human bodies, philosophy books, tables, chairs, and so on. These physical objects continue to exist whether or not they are perceived. In addition, these objects are also assumed to actually be as they appear to us, for example goldfish are truly gold, footballs are spherical. Common Sense Realism assumes that our sensory organs are generally reliable and that they give us a realistic sense of the external world.
Representative Realism is called "representative" because it suggests that all perception is a result of awareness of inner representations of the external world. When I see s seagull I do not see it directly in the way that common sense realism suggests. I have no direct sensory contact with the bird. Rather, what I am aware of is a mental representation, something like an inner picture, of the sea gull. My visual experience is not directly of the seagull, though it is caused by it, but rather it is experience of the representation of the seagull my senses produce.
