Outline the argument from illusion against direct realism

According to direct realism, we perceive objects in the external world directly. This is contrasted with indirect realism, which holds that the immediate objects of perception are mental representations or sense data that represent objects in the external world. Direct realism does not deny that perception involves perhaps quite complex causal chains, where e.g. photons must travel from the object to my retina; but it holds that the photons, the pattern of stimulation on the retina, etc, are not themselves perceived but are part of the mechanism of perception. ¶ The argument from illusion rests on the phenomenal principle, which states that if an object appears to you to have some property F, then what you are directly perceiving does in fact have property F. Consider looking at a stick half-submerged in water. By the phenomenal principle, it follows that you are directly perceiving something that is bent. But the stick itself is not bent, nor is any other mind-independent object in the vicinity bent. Therefore, you are not directly perceiving any mind-independent object when you look at the stick. The next step of the argument claims that illusory experiences and veridical perception should be explained in terms of the same theory of perception. So, since we do not directly perceive mind-independent objects during illusions, we also do not directly perceive mind-independent objects in veridical perception.