There seems to be no sudden break between our most sober every-day recognitions of familiar objects and the wildest hallucinations of the demented.

As we pass from the former to the latter, we find that there is never any abrupt transition, never any addition of perfectly new elements, but only that the old elements go on combining in ever new proportions.
The connection between the illusory side of our life and insanity may be seen in another way.

All illusion has as its negative condition an interruption of the higher intellectual processes, the due control of our mental representations by reflection and reason.

In the case of passive illusions, the error arises from our inability to subordinate the suggestion made by some feature of the present impression to the result of a fuller inspection of the object before us, or of a wider reflection on the past.

In other words, our minds are dominated by the partial and the particular, to the exclusion of the total or the general.