The self, defined as an absolute, unchanging entity, which possesses unity, continuity and clear boundaries, may well be an illusion.
Unity and continuity are easily disrupted in the normal course of life; they may be merely coincidental. Our supposedly unchanging selves do in fact alter according to their circumstances; the boundaries of the self change and a single self may even split to form multiple selves. By examining the self in terms of unity, continuity and boundaries, I will show how the possibilities for disruption of the self, as defined above, imply that it could be an illusion.
Unity of a self implies that there is something that unites all my thoughts, feelings and experiences, i.e. that there is some sort of glue that makes them all true of me. The tendency is to call the glue the "self". Locke defined this as consciousness, that is, a person being "self to itself" by its consciousness of its present thoughts and actions .
So a single seat of consciousness may be termed a single self.
This definition holds for my waking hours; however, there are obvious disruptions. What happens when I am anaesthetized, or fall into a deep sleep? I am not conscious of my present thoughts; I cannot even be said to have any "present thoughts". There are no experiences to be glued together, and there is no glue to bind them. Even when I dream, I may not be myself in my dream; I may, for example, be a butterfly . If the unified "I", as defined above, can somehow cease to exist for a time or be different things at different times, then unity, as defined by Locke, may be merely coincidental.
The second question is that of continuity, that is, the sameness of the self over time.