Chapter 18
The Way We Think Of The Imagination (Continued)
366. Our way of explaining how we conceive of phantasy can also help us to understand how images sometimes differ either in vividness or in quality from sensations, which they may surpass or belie. Notable differences will cause no surprise when we realise that the movement or nerve alteration which precedes feeling depends upon a stimulus of images differing from that of sensations. The internal stimulus acts according to different laws from those which govern bodies acting upon our external senses.
But it helps us to understand not only the difference between images and sensations: it also explains how they are sometime so similar that we cannot distinguish them in any way, nor decide whether an object is present or not. There is nothing to prevent the nerve alteration produced by the internal cause from being so perfect that it is the same as the change produced by the external cause.
Many other questions could be raised about the faculty of imagination. For example: `Why is the soul capable of arousing only sensations already experienced, but completely incapable of arousing new sensations?' This, however, would lead us too deeply into the study of the activity of the sensitive soul and the laws according to which it operates. We shall examine the matter in the second section of this book, therefore, which we begin immediately.
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