There are many things that people sometimes claim they “see” that really aren’t there. They may have visions of “ghosts” or strange creatures. Sometimes little children claim they “saw” things that no one else did. Sometimes these are fantasies or day dreams; sometimes they are illusions.

There is a difference between an illusion and an hallucination. When a person has an illusion, there is something present that stimulates the eyes or senses. It can be verified, because other people see it, too. A mirage, for example, is a kind of illusion. But the main point is that something is there that causes the person to think he saw what he saw.