Final answer:
The idea that dreams are crucial for understanding mental illness is attributed to Sigmund Freud, who considered dreams a window to the unconscious mind. Carl Jung and Rosalind Cartwright later offered alternative theories, with Jung focusing on the collective unconscious and Cartwright emphasizing personal significance and empirical evidence.
Step-by-step explanation:
The original idea that dreams play an important role in understanding mental illness can be primarily credited to Austrian psychiatrist Sigmund Freud.
Freud believed that dreams are the 'royal road' to the unconscious mind and through the analysis of dreams, particularly their manifest and latent contents, one could gain insights into mental processes that are otherwise not accessible. While Freud's ideas were groundbreaking, various criticisms have been raised regarding his dream theory. Critics suggest that the interpretation of dreams is too subjective and lacks empirical support.
Moreover, other theorists like Carl Jung and Rosalind Cartwright have contributed different perspectives on the significance of dreams. Jung posited that dreams connect us to the collective unconscious, a reservoir of universal symbols and meanings shared among all humans, while Cartwright's research indicates that dreams often reflect important life events of the dreamer, which she and other researchers have backed with empirical evidence.