 Siewert (1998) asks his readers to compare an experience of hearing or reading a sentence without understanding, as when one reads a difficult passage without paying attention to it, and an experience of hearing or reading a sentence with understanding. There is clearly a phenomenal difference between these cases. Siewert argues that the difference is not a difference in verbal or perceptual imagery, since the verbal and perceptual imagery might be the same in both cases. The best explanation of the phenomenal contrast is that thought involves proprietary cognitive phenomenology. 