Sigmund Freud revolutionized our understanding of dreams by proposing that they are a window into the unconscious mind. According to Freud, dreams are not mere stories our minds create while we sleep but are profoundly meaningful narratives about our hidden desires and fears. He introduced two key concepts: manifest content and latent content. The manifest content is the actual content and imagery of the dream — what we remember when we wake up. The latent content, however, represents the underlying, hidden meaning of the dream, revealing our unconscious wishes.

Freud's approach requires the dreamer to explore the symbolic meanings of dream elements. For instance, a dream about a train ride might seem straightforward. Still, Freud would suggest that each aspect of the dream, including the train and the act of riding, could symbolize deeper, unconscious issues or desires needing interpretation.

Freud's theories paved the way for other psychologists, including Carl Jung, who expanded the theory to include collective unconscious elements shared across humanity, manifesting in dreams through universal symbols or archetypes.

In contrast to these psychoanalytical views, more contemporary theories have shifted the perspective on dreams. For example, the cognitive theory of dreaming posits that dreams are essentially an extension of our waking thought processes, functioning as mental simulations that occur while we sleep. This perspective suggests that the themes and concerns we engage with during the day continue to influence our thoughts and dreams, effectively blurring the line between our conscious and unconscious cognitive activities.

Similarly, the activation-synthesis theory posits that dreaming occurs when the cerebral cortex synthesizes neural signals generated from activity in the lower part of the brain. Dreams result from the brain's attempts to find logic in random brain activity that occurs during sleep.

Despite the diverse views on their purpose and meaning, dreams continue to be a rich subject for psychological research and theory, reflecting the evolving understanding of the human mind.