Simple recollective processes by no means give an adequate picture of reality. In the tenth chapter of his book on illusions Sully gives such a list and description of important mental illusions as is calculated to shake our faith in the trustworthiness of memory. It seems that our recollections are often mere fragments of a formerly well-known whole (we may recall, for example, only one or two features of an acquaintance), and as a result of this analytic process we are prone to make new combinations of the detached elements. Thus, a short time ago I thought that I could clearly picture to myself the house of my brother-in-law by the power of association, but I afterward discovered that I had conceived the bricks to be far too bright a red, and had evidently substituted the colour of some other house. What we call constructive imagination then turns out to be constantly renewed manipulation of previously verified impressions. We need not here touch upon the wide field of involuntary productive imagination, since it is only play directed by the will that is engaging us; yet before going on to concrete cases, it should be stated that in constructive imagination as well the pictures formed are to a considerable extent involuntary, the will aiding more by its influence in concentrating the attention on the trend of the internal processes and in discriminating between them, than in forming the picture itself. This is why the efforts of great artists are so often like inspirations. Building air castles is the simplest exercise of constructive imagination.[296] It most commonly manifests itself as voluntary playful forming of cheerful and ambitious images of ourselves or our friends amid the most fortunate surroundings.[297] We may see how it is done by watching little children who have enjoyed a new kind of treat at a birthday party or some such occasion—how they will remember and repeat it in their future plays. All the details will be copied sometimes just as in the model, sometimes in new combinations, or turned into a joke. The inestimable value of such play for making life worth living is self-evident. It veils the sordidness of everyday existence with a double illusion, the first being our conception of the air castle as a reality, and so getting immediate possession of this radiant dream (here the two kinds of imagination converge). Such illusion supplies the psychological interest in Faust’s bargain; he enjoys the “schönsten Augenblick,” although his present satisfaction is merely premonitory. The second illusion is exemplified in our implicit trust that the future will verify our hope,[298] that buoyant and vivifying emotion which accompanies us all through life.