For example, it might be found that introspection, or the immediate inspection of our own feelings or mental states, does not supply the conditions necessary to the production of such error.

And, indeed, it is probable that most persons, antecedently to inquiry, would be disposed to say that to fall into error in the observation of what is actually going on in our own minds is impossible.
With the exception of this first division, however, this scheme may easily be seen to answer to actual phenomena.

That there are illusions of perception is obvious, since it is to the errors of sense that the term illusion has most frequently been confined.

It is hardly less evident that there are illusions of memory.

The peculiar difficulty of distinguishing between a past real event and a mere phantom of the imagination, illustrated in the exclamation, "I either saw it or dreamt it," sufficiently shows that memory is liable to be imposed on.