  Sturgeon points to a number of features that can be common to veridical perceptions, illusions, and hallucinations. Among the features he points to are the following: (i) veridical perceptions, illusions and hallucinations can produce similar behavioural effects. For example, in general, if it sensibly appears to you as though a rock is flying towards you, you will duck, irrespective of whether the experience you are having is a veridical perception, an illusion, or a hallucination. (ii) If, on the basis of that experience, you believe that a rock is flying towards you, and you act on that belief and duck, there is a sense in which your belief and action are rational, irrespective of whether that experience is a veridical perception, an illusion, or a hallucination. (iii) If you have an experience as of a rock flying towards you, you can know what it’s like to see a rock flying towards you, irrespective of whether that experience is a veridical perception, an illusion, or a hallucination. (iv) Veridical perceptions, illusions and hallucinations can be introspectively indistinguishible.