 Our sense-organs enable the mind to receive ideas of objects and events in our immediate environment. Some of these ideas, those of the primary properties or qualities, such as shape, size, and solidity, are both caused by and standardly resemble those qualities as they actually are in the objects themselves. Thus the computer screen I am looking at now looks oblong and is oblong. Under ideal conditions, the way the primary qualities of an object appear accurately represent its real nature, both as portrayed by common sense and as understood by scientific investigation. By contrast, the ideas of secondary qualities do not resemble the properties in the object that cause us to have those ideas. There is nothing in the objects themselves that resembles our ideas of color, sound, and so on. The story, as revealed by scientific investigation, of what is going on in the physical world when someone sees a red ball, or smells the aroma of their morning coffee, would not mention colors or smells at all. Rather, the objects in question are so constituted that, in suitable conditions, they emit waves or particles that stimulate the sense-organs in certain ways causing us to have the characteristic secondary quality experience. The full scientific account of how this happens is complicated, more complicated than people in Locke’s time realized, but however the story goes, there will be nothing in the world at all like colors-as-we-see-them, or sounds-as-we-hear-them. Since the ideas of secondary qualities that arise in our minds when our sense-organs are stimulated depend on the nature and constitution of our sensory apparatus, as well as on the nature of external reality, it follows that creatures whose sense-organs differ from ours would have a different kind of secondary quality experience. Nor is this merely a thought experiment; it seems that insects, for example, make color distinctions that do not match ours in significant respects.