Ayer thinks the theory that the first thing you"re aware of when you open your mind is an object cannot explain illusions, delusions is false. When the brain is stimulated a mental image appears in your minds eye. When you open your eyes, the first thing you"re aware of isn"t the object, but the presence of the object in your mind. (theory of indirect perception) Sense data non-physical object that exists only in the mind of the observer. Ayer argues that all we"re aware of is sense data. Sometimes sense data is caused by things it resembles (accurate perceptions) Representational theory of perception, indirect theory of perception. Na ve realism (theory of direct perception) the first thing you see is the object in the real world. Theory of indirect perception the first thing you see isn"t in the real world, but a mental image.