In active illusions, again, the powers of judgment and reflection, including those of calm perception itself, temporarily vacate their throne in favour of imagination.

And this same suspension of the higher intellectual functions, the stupefaction of judgment and reflection made more complete and permanent, is just what characterizes insanity.
We may, perhaps, express this point of connection between the illusions of normal life and insanity by help of a physiological hypothesis.

If the nervous system has been slowly built up, during the course of human history, into its present complex form, it follows that those nervous structures and connections which have to do with the higher intellectual processes, or which represent the larger and more general relations of our experience, have been most recently evolved.

Consequently, they would be the least deeply organized, and so the least stable; that is to say, the most liable to be thrown _hors de combat_.

This is what happens temporarily in the case of the sane, when the mind is held fast by an illusion.