As we have seen, Whitehead believes that in sense-perception we only obtain a simplified version of physical reality. We experience our common-sense world in what Whitehead calls perception in the mode of presentational immediacy, as made up of spatial regions marked out by clear-cut sensory qualities — coloured patches, tactual expanses, volumes of sounds, etc. -occurring at definite moments of time. On a somewhat different level, images occur in such mental states as memory and imagination. Although images have a similar structure to our percepts, i.e., they are qualities predicated of certain places and times, Whitehead would not accept Hume's view that they are merely faint copies of these percepts. He does allow that we have a capacity to generate new types of ideas.