Let us now ascertain the cause of the various psychical and physiological conditions which aim at and often succeed in presenting to the mind a mere representative sign as a substantial and real image.  What is the cause of the apparent reality of dreams?  The image is clearly a psychical phenomenon, containing a sensible element of which we are conscious; the fundamental faculty of the perception is exerted on it as on a real object, and the immediate results are precisely identical.  The reader will remember that we have shown that a phenomenon involves the intuitive idea of an active subject, so that the image also, in accordance with the innate faculty of perception, must normally appear to the mind as such.  When this is not the case, it is because the normal effect of natural phenomena, to which our attention is constantly directed, and our mental education and hereditary influence, have accustomed us to distinguish at once between the mere idea and the real object, and thus we discern the difference between the normal action of thought and sense, and illusions, hallucinations, and dreams.  But since these psychical and physiological conditions lose their force when the habit and actions of our waking state are dormant, the primitive and innate entification of the image quickly recurs, as we can plainly see from the previous analysis.

This is so much the case, that some savage peoples even now find it hard to distinguish real events from those of dreams, and this is owing to a defect in their memory or to the imperfection of their language.  In fact, all civilized and barbarous peoples in the world have without exception believed, and still believe, in the reality of images seen in dreams, and their personification has been the source of an immense number of myths.  Even now, with all our civilization and advanced science, not only the common people, but many of those in fashionable and tolerably cultivated society, believe in the reality of dreams and in their hallucinations, and derive from them fears, hopes, and warnings for their future life.

I will give one instance in a thousand to prove the innate tendency even in the act of dreaming to transform the image into a real object.  It appeared to me that I was in a large room filled with acquaintances and strangers, who discussed an event which had really occurred in the city a few days before.  All at once I raised my eyes to the wall of the room, and saw a large picture, representing a landscape with distant mountains, streams, cottages, and animals.  As I looked, the picture was gradually transformed into a real object, and I found myself, together with the company before mentioned, in the midst of the fields, on the bank of the river, and within one of the cottages.