  But is sense perception reliable? Perceptual errors and dreams seem to indicate that things are not always as they seem. Autrecourt discusses several sceptical doubts (dubia), versions of what would later be called the “argument from illusion” and the “argument from dreaming”. These arguments work from the common sense assumption that things often appear to be other than they are: e.g., sweet food can appear bitter, a white object can appear red, in sleep it can seem to someone that he is flying through the air or fighting the Saracens.