Dreams are very different from waking life, but it is extremely difficult clearly to define in what the difference consists. When we are dreaming, we are nearly always convinced that we are awake, and in some cases real experiences have been mistaken for dreams.
The latter mistake forms the subject of a celebrated Spanish play called Life a Dream, and of an amusing story in the Arabian Nights, in which a poor man is for a jest treated as a mighty monarch, and it is contrived that he should afterwards think that all the honourable treatment he had actually received was merely a vivid dream.
Sometimes even after waking, we may be doubtful whether our dream was a reality or not, especially if we happen to fall asleep in our chair and do not remember the circumstance of having fallen to sleep. Of course this doubt can only arise when there has been nothing in our dream that seems impossible to our wakened mind.
It is, however, only in rare cases that a dream exactly copies the experience of our waking hours. As a rule, in our sleep all kinds of events seem to happen which in our waking hours we should know to be impossible. In our dreams we see and converse with friends who are at the other side of the world or have been long dead.
We may even meet historical or fictitious characters that we have read about in books. We often lose our identity and dreams that we are someone else, and in the course of a single dream may be in turn several different persons. Space and time to the dreamer lose their reality.
It is possible in a dream that lasts a few seconds to appear to have gone through the experience of many years. The limitations of space may also vanish into nothing, so that we seem to travel the most distant parts of the universe with the rapidity of thought.
Our imagination gains in some cases such complete control over our reason that we can contemplate all such contradictions to our ordinary experience without the least feeling of wonder. But this is not always the case. It is impossible to assert as a universal rule that in a dream nothing, however extraordinary, can surprise us.
Sometimes dreamers do have feeling of wonder at their strange experiences. Nor can we say that the moral reason loses all control in our sleep.
It does indeed sometimes happen that good men in their dreams seem to do without the slightest compunction horribly wicked deeds, but, on the other hand, even the dreamer sometimes hears the voice of conscience.
The origin of dreams may in many cases be traced to internal or external causes. Nightmare is frequently due to indigestion or ill-health.
When a dream is connected with an external cause, it is often possible to trace some resemblance between the cause and the effect, although our imagination erects a great dream fabric on a very small foundation.
Instances are quoted of a dreamer who dreamt that he was wandering through regions of polar ice and woke up to find that he had kicked off his bedclothes; and of another who, going to sleep with a hot bottle at his feet, dream that he was walking over the crater of a volcano.
The sound of a whistle heard at the moment of waking may make us dream of a long-continued struggle to catch a railway train on the point of starting.
In other cases a dream originates in something that the dreamer saw or we thinking about just before sleep came upon him. Coleridge once fell asleep in his chair after reading how Kubla Khan ordered a palace to be made. The idea worked upon his imagination, and the consequence was that he composed a fine poem in his sleep.
When he woke up, he remembered perfectly the lines that had presented themselves to his mind in the form of a dream, and he immediately began to write them down. Unfortunately he was interrupted in the middle of his task by a visitor, after whose departure he could remember no more, so that the poem is only a fragment.
Not only the imagination but also the reason has been known to do good work in dreams. There are instances of mathematicians solving in their sleep problems that they had vainly puzzled over when awake.
All the fact that we have been considering are so various that they chiefly illustrate the extreme difficulty of making any general statement about dreams.
They show that in many cases dream- life is very different from real life, and that in other cases mind of a sleeping man works much in the same way as if he were awake.
Perhaps the only definite general statement that can be made on the subject is that imagination even in sleep cannot originate anything, although it has an almost unlimited power of uniting together in more or less unusual or even in impossible combinations what we have actually experienced.