Aristotle wrote two short pieces on dreams and their meaning: On Dreams and On Prophesying on Dreams. In the first he presents arguments for the origin of dreams and their relationship to other aspects of human existence. In the second he analyzes whether dreams can foreshadow the future.
Aristotle approaches his subject as a scientist, looking for a practical explanation for an experience men found mysterious and frightful. Given that the only ways to acquire knowledge are through sense perception or intelligence, and that our senses are not operating during sleep, he asserts that the senses cannot contribute to dreaming. That means dreams must originate in our intellect. Of course the experiences in dreams are still based on sense perception (we see things when we dream), but that experience is disconnected from reality.