 Fortunately, it is relatively clear what phenomena are: “appearances to the extent that as objects they are thought in accordance with the unity of the categories are called phenomena” (A249). Earlier, in the “Aesthetic”, Kant had defined appearance as: “the undetermined object of an empirical intuition” (A20/B34). All objects of empirical intuition are appearances, but only those that are “thought in accordance with the unity of the categories” are phenomena. For instance, if I have a visual after-image or highly disunified visual hallucination, that perception may not represent its object as standing in cause-effect relations, or being an alteration in an absolutely permanent substance. These would be appearances but not phenomena. The objects of “universal experience”, as defined in section 3, are phenomena because the categories determine the a priori conceptual form; universal experience represents its objects under the unity of the categories.