āOn Dreamsā is part of Aristotleās Parva Naturalia, a collection of works on the phenomena of human life. In this treatise, he hypothesizes that we dream because our sensory organs continue to function while we sleep. He compares dreams to hallucinationsāerrors in our sense perception. Aristotleās view of dreams influenced philosopher Thomas Hobbes and psychologist Sigmund Freud, and it continues to fascinate readers today.