On the other hand, the active illusions, being essentially individual or subjective, may be said to correspond to the other variety of this class--those connected with variations of sensibility.
Our scheme of sense-illusions is now complete.

First of all, we shall take up the passive illusions, beginning with those which are conditioned by special circumstances in the organism.

After that we shall illustrate those which depend on peculiar circumstances in the environment.

And finally, we shall separately consider what I have called the active illusions of sense.
It is to be observed that these illusions of perception properly so called, namely, the errors arising from a wrong interpretation of an impression, and, not from a confusion of one impression with another are chiefly illustrated in the region of the two higher senses, sight and hearing.

For it is here, as we have seen, that the interpretative imagination has most work to do in evolving complete percepts of material, tangible objects, having certain relations in space, out of a limited and homogeneous class of sensations, namely, those of light and colour, and of sound.