Thus, when a patient takes any small objects, as pebbles, for gold and silver, under the influence of the dominant idea of being a millionaire, it is obvious that external suggestion has very little to do with the self-deception.

The confusions into which the patient often falls with respect to the persons before him show the same state of mind; for in many cases there is no discoverable individual resemblance between the person actually present and the person for whom he is taken.
It is evident that when illusion reaches this stage, it is scarcely distinguishable from what is specially known as hallucination.

As I have remarked in setting out, illusion and hallucination shade one into the other much too gradually for us to draw any sharp line of demarcation between them.

And here we see that hallucination differs from illusion only in the proportion in which the causes are present.

When the internal imaginative impulse reaches a certain strength, it becomes self-sufficient, or independent of any external impression.
This intimate relation between the extreme form of active illusion and hallucination may be seen, too, by examining the physical conditions of each.