The Dialogue of Dreams

Are dreams a source of reliable divination? Generations upon generations seem to have thought so. They incubated dreams by travelling afar, by fasting and by engaging in all other manners of self deprivation or intoxication. With the exception of this highly dubious role, dreams do seem to have three important functions:

To process repressed emotions (wishes, in Freud's speech) and other mental content which was suppressed and stored in the unconscious.
To order, classify and, generally, to pigeonhole conscious experiences of the day or days preceding the dreaming ("day residues"). A partial overlap with the former function is inevitable: some sensory input is immediately relegated to the darker and dimmer kingdoms of the subconscious and unconscious without being consciously processed at all.
To "stay in touch" with the outside world. External sensory input is interpreted by the dream and represented in its unique language of symbols and disjunction. Research has shown this to be a rare event, independent of the timing of the stimuli: during sleep or immediately prior to it. Still, when it does happen, it seems that even when the interpretation is dead wrong - the substantial information is preserved. A collapsing bedpost (as in Maury's famous dream) will become a French guillotine, for instance. The message conserved: there is physical danger to the neck and head.
All three functions are part of a much larger one: