Other and grosser illusions connected with personal identity are also found to be closely related to defects or disturbances of the ordinary mnemonic process, and so can be best treated here.

In order to understand these, we must inquire a little into the nature of our idea and consciousness of a persistent self.
Here, again, I would remind the reader that I am treating the point only so far as it can be treated scientifically or empirically, that is to say, by examining what concrete facts or data of experience are taken up into the idea of self.

I do not wish to foreclose the philosophic question whether anything more than this empirical content is involved in the conception.
My idea of myself as persisting appears to be built up of certain similarities in the succession of my experiences.

Thus, my permanent self consists, on the bodily side, of a continually renewable perception of my own organism, which perception is mainly visual and tactual, and which remains pretty constant within certain limits of time.

With this objective similarity is closely conjoined a subjective similarity.