Traditionally, the sense datum view is pitted against naive realism. This chapter deals with naive realism and formulates the sense datum view. Sense datum theorists focused on visual experience. However, Russell, Moore, and Price applied the theory to all sensory-perceptual experiences. Many sense datum theorists said that visual sense data are indeed flat or two-dimensional. To have a sensory-perceptual experience with a certain character is to stand in the experiencing relation to certain states, like the redness and roundness of something or the movement of something from one place to another. People have different sensory-perceptual experiences if, and only if, they experience different such states. In the actual world, these states always wholly concern sense data. In effect, the sense datum theory is the act-object assumption together with the claim that the relevant “objects” are always non-physical sense data created by the brain. These objects exist, even though they are non-physical.