Hume’s A Treatise of Human Nature (I, iv, 6): Personal Identity

Some philosophers believe this:

We are every moment intimately conscious of what we call our self; we feel its existence and its continuing to exist, and are certain - more even than any demonstration could make us - both of its perfect identity and of its simplicity. The strongest sensations and most violent emotions, instead of distracting us from this view ·of our self·, only focus it all the more intensely, making us think about how these sensations and emotions affect our self by bringing it pain or pleasure. To offer further evidence of the existence of one’s self would make it less evident, not more, because no fact we could use as evidence is as intimately present to our consciousness as is the existence of our self. If we doubt the latter, we can’t be certain of anything.

Unfortunately, all these forthright assertions are in conflict with the very experience that is supposed to support them. We don’t so much as have an idea of self of the kind that is here described. From what impression could this idea be derived? This question can’t be answered without obvious contradiction and absurdity; yet it must be answered if the idea of self is to qualify as clear and intelligible. Every real idea must arise from some one impression. But self or person is not any one impression, but is rather that to which all our many impressions and ideas are supposed to be related. If the idea of self came from an impression, it would have to be an impression that remained invariably the same throughout our lives, because the self is supposed to exist in that way. But no impression is constant and invariable. Pain and pleasure, grief and joy, passions and sensations follow one other and never all exist at the same time. So it can’t be from any of these impressions or from any other that the idea of self is derived. So there is no such idea.
               Furthermore, if we retain this hypothesis about the self, what are we to say about all our particular perceptions? They are all different, distinguishable, and separable from one other - they can be separately thought about, and can exist separately - with no need for anything to support their existence. In what way do they belong to self? How are they connected with it? For my part, when I look inward at what I call myself, I always stumble on some particular perception of heat or cold, light or shade, love or hatred, pain or pleasure, or the like. I never catch myself without a perception, and never observe anything but the perception. When I am without perceptions for a while, as in sound sleep, for that period I am not aware of myself and can truly be said not to exist. If all my perceptions were removed by death, and I could not think, feel, see, love or hate after my body had decayed, I would be entirely annihilated - I cannot see that anything more would be needed to turn me into nothing. If anyone seriously and thoughtfully claims to have a different notion of himself, I can’t reason with him any longer. I have to admit that he may be right about himself, as I am about myself. He may perceive something simple and continued that he calls himself, though I am certain there is no such thing in me.
               But setting aside metaphysicians of this kind, I am willing to affirm of the rest of mankind that they are nothing but a bundle or collection of different perceptions that follow each other enormously quickly and are in a perpetual flux and movement. Our eyes can’t turn in their sockets without varying our perceptions; our thought is still more variable than our sight; and all our other senses and faculties contribute to this change in our perceptions, with no one of them remaining unaltered for a moment. The mind is a kind of stage on which many perceptions successively make their appearance: they pass back and forth, glide away, and mingle in an infinite variety of positions and situations. Strictly speaking, there is no simplicity in the mind at one time and no identity through different times, no matter what natural inclination we may have to imagine that simplicity and identity. ·That is to say: It is not strictly true that when a blue colour is seen and a whistling sound heard at the same time, one single unified mind has both these perceptions; nor is it strictly true that the mind that has a certain perception at one time is the very same mind that has a perception at another time·. The ‘stage’ comparison must not mislead us. What constitutes the mind is just the successive perceptions; we haven’t the faintest conception of the place where these scenes are represented or of the materials of which it is composed.

Fred Feldman, A Cartesian Introduction to Philosophy:

"If you want to pursue this point a bit further, perhaps you should try a little experiment. Look as carefully as you can into your own experiences. Reflect intently on how you feel, and what you see. Perhaps you see various colors, and feel warmth, or chilliness. Maybe you can feel some pressure on some parts of your body. These are all properties that you are experiencing. Now look even closer, and see if you can see a "self" or an "ego" or a "me" that is the subject of all these experiences. If Russell is right, you will not find any such entity. At best, you can assume that it is there, serving as a support for all the properties that you can experience."