It will perhaps be proper not to reduce all the phenomena of paramnesia to the same conditions. Only a limited number of them seem to be so reducible. Impressions often occur which one is inclined to attribute to illusory memory, merely to discover later that they were real but unconscious memory; the things had been actually experienced and the events had been forgotten. So, for example, I visit some region for the first time and get the impression that I have seen it before, and since this, as a matter of fact, is not the case, I believe myself to have suffered from an illusion of memory. Later, I perceive that perhaps in early childhood I had really been in a country that resembled this one. Thus my memory was really correct; I had merely forgotten the experience to which it referred. Aside from these unreal illusions of memory, many, if not all others, are explicable, as Sully indicates, by the fact that something similar to what has been experienced, has been read or heard, while the fact that it has been read or heard is half forgotten or has sunk into the subconsciousness. Only the sensation has remained, not the recollection that it was read, etc. Another part of this phenomenon may possibly be explained by vivid dreams, which also leave strong impressions without leaving the memory of their having been dreams. Whoever is in the habit of dreaming vividly will know how it is possible to have for days a clear or cloudy feeling of the discovery of something excellent or disturbing, only to find out later that there has been no real experience, only a dream. Such a feeling, especially the memory of things seen or heard in dreams, may remain in consciousness. If, later, some similar matter is really met with, the sensation may appear as a past event.[234] This is all the easier since dreams are never completely rigid, but easily modeled and adaptable, so that if there is the slightest approximation to similarity, memory of a dream lightly attaches itself to real experience.