“Alas! it is delusion all: 
   The future cheats us from afar,
   Nor can we be what we recall,
   Nor dare we think on what we are.”

It must be confessed that our study has tended to bring home to the mind the wide range of the illusory and unreal in our intellectual life.  In sense-perception, in the introspection of the mind’s own feelings, in the reading of others’ feelings, in memory, and finally in belief, we have found a large field for illusory cognition.  And while illusion has thus so great a depth in the individual mind, it has a no less striking breadth or extent in the collective human mind.  No doubt its grosser forms manifest themselves most conspicuously in the undisciplined mind of the savage and the rustic; yet even the cultivated mind is by no means free from its control.  In truth, most of the illusions illustrated in this work are such as can be shared in by all classes of mind.

In view of this wide far-reaching area of ascertained error, the mind naturally asks, What are the real limits of illusory cognition, and how can we be ever sure of having got beyond them?  This question leads us on to philosophical problems of the greatest consequence, problems which can only be very lightly touched in this place.  Before approaching these, let us look back a little more carefully and gather up our results, reflect on the method which we have been unconsciously adopting, and inquire how far this scientific mode of procedure will take us in determining what is the whole range of illusory cognition.

We have found an ingredient of illusion mixed up with all the popularly recognized forms of immediate knowledge.  Yet this ingredient is not equally conspicuous in all cases.  First of all, illusion varies very considerably in its degree of force and persistence.  Thus, in general, a presentative illusion is more coercive than a representative; an apparent reality present to the mind is naturally felt to be more indubitable than one absent and only represented.  On the other hand, a representative illusion is often more enduring than a presentative, that is to say, less easily found out.  It is to be added that a good deal of illusion is only partial, there being throughout an under-current of rational consciousness, a gentle play of self-criticism, which keeps the error from developing into a perfect self-delusion.  This remark applies not only to the innocent illusions of art, but also to many of our every-day illusions, both presentative and representative.  In many cases, indeed, as, for example, in looking at a reflection in a mirror, the illusion is very imperfect, remaining in the nascent stage.