Imagination is the act of bringing back into the mind impressions or images not presently available to the sense. In the simplest form of imagination, memory, the images appearing in the mind are based wholly on something earlier perceived. It requires little effort, for example, for a person to bring to mind a picture of the breakfast he ate that day.

Imagination may also include not just reconstructing past experiences but also creating mental images from partly noticed experiences. For example, a baseball fan was busy eating his popcorn and so missed seeing the batter hit the home run although he did look up in time to see the ball as it cleared the fence. In his imagination the fan can recreate the whole event (the pitcher winding up and throwing, the batter flexing his muscles and smashing the ball, and the center fielder running in vain), even though he did not actually see all these events taking place.

Individuals are said to have a good imagination when they are able to take images and put them together into an unusual mental picture, often of events that never took place. Such a person, when asked to write a story entitled "I Was the First Man on Mars," would quickly create a story, complete with elaborate details, while people with poor imaginations would sit back unproductively. Creative artists, such as novelists and playwrights, are gifted with active imaginations, and great scientists often are also. Children seem to have more creative imaginations than most adults. A three-year-old, for example, may play happily with an imaginary friend for hours. As the child grows older he tends to repress images that do not make sense to persons around him. Nevertheless, most adults indulge in daydreams from time to time as a relief from the monotony or unpleasantness of real life.

Eidetic imagery occurs when a person in his imagination is able to recall a complicated experience exactly as it happened. Persons with this so-called photographic memory can recall all the details of a picture as though the picture were still in front of them, and those persons with acoustic eidetic imagery can repeat a long list of words after hearing them only once. Young children seem to have this capacity more than adults.