Hume’s empiricism asserts no idea without a corresponding sense impression. Therefore we cannot have a concept of something we’ve never experienced before. For example: I have an idea/concept of an apple in virtue of the fact that I’ve perceived an apple many times before.
Do we have an idea of an enduring self? “[F]rom what impression cou’d this idea be derived?” What kind of impression would this have to be? It would have to be an impression of something that remains the same throughout our entire lives. Do you have any such impression?
Hume claims that he does not:
“But there is no impression constant and invariable. Pain and pleasure, grief and joy, passions and sensations succeed each other, and never all exist at the same time. It cannot, therefore, be from any of these impressions, or from any other, that the idea of self is deriv’d; and consequently there is no such idea”
Locke admits that our impressions are constantly changing, but maintains that our consciousness or awareness remains unchanged. Though our sense impressions are perpetually in flux, the person perceiving the sense impressions remains the same. But remember Hume’s cardinal rule: no idea without a corresponding impression. Do we have an impression of this consciousness that Locke supposes remains the same over time?
No! “For my part, when I enter most intimately into what I call myself, I always stumble on some particular perception or other, of heat or cold, light or shade, love or hatred, pain or pleasure. I never can catch myself at any time without a perception, and never can observe anything but the perception.” – David Hume
So, if we are not a perceiving subject that remains the same over time, what are we? We are simply the bundle of our ever-changing impressions:
“…I may venture to affirm of the rest of mankind, that they are nothing but a bundle or collection of different perceptions, which succeed each other with an inconceivable rapidity, and are in a perpetual flux and movement. Our eyes cannot 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; nor is there any single power of the soul, which remains unalterably the same, perhaps for one moment” – David Hume
This is the only concept of a self that we can gain by carefully examining the contents of our experiences, Why do we think that persons, animals and things remain the same over time? Why do you think that your dog remains the same over time? Is there anything in your impression of your dog that remains the same every time you perceive it? No! Your dog’s fur turns gray, its eyes cloud over, its limbs become arthritic, its teeth get worn down, etc.
However If you took your dog to the vet and picked up a qualitatively similar dog (same size, same colouring, same eyes, etc.), you would notice in fairly short order that the dog you’ve picked up is not yours. Doesn’t this indicate that your dog does have an identity that remains unchanged? How do you determine that the dog you’ve brought home is not yours? Perhaps it barks more often, nips at you, knocks down children, doesn’t respond to its name, etc.
Thus, you do not have an impression of your dog’s unchanging essence. Instead, you judge this dog not to be yours on the basis of the discrepancy that exists between the bundle of impressions that you identify as your dog and the behaviour of the dog that you’ve brought home. Why do we think that dogs, animals and plants have identities that remain the same over time?
In part, we think so because the changes that they undergo in a short amount of time are relatively minor and the significant changes that they endure are drawn out over a long period of time. A dog may shed 1/1000th of its fur in a day, but the changing of a dog’s fur from black to gray takes place over a matter of years. Either way, we tend not to notice the change. Our impressions, however, do change suddenly and noticeably, so why do we think that our selves remain the same over time?
What makes us think that we remain the same person over time? What makes us think that amidst the bundle of our ever-changing impressions, there exists an impression of a static conscious agent? What is it about the character of our experiences that makes us think that they are happening to a static subject?
The illusion is an effect of the way in which our impressions manifest themselves, or as Hume puts it, of the relations that exist between our impressions. When examined closely, our experience actually consists in a series of “still shot” impressions of the world. If we experienced the world as a series of random, stilted impressions, then we would have no notion of identity or personal identity.
In other words, the psychological continuity that Locke sees as being the seat of personal identity is not a product of our impressions, but of how they are strung together. What fills in the gaps between our impressions, thus creating the illusion of continuous conscious experiences, are the relations that the imagination imposes on our impressions to make them intelligible. We think that we are engaged in the activity of playing fetch with our dog because our impressions of our dog bear the relation of resemblance to one another and seem to be connected in a causal sequence: I throw the ball, the dog sees the ball, fetches the ball, and returns it.
The relations of similarity and causation are imposed on the impressions by the imagination, they cannot be found in the impressions themselves. The imagination is like a movie reel that connects a series of pictures. If you slow the movie down, you lose the sense of observing a scene. It is our memory that makes it possible for our imagination to impose the relations of resemblance and causation on our impressions.
I can notice that the impression I have of my dog right now resembles the impression of my dog five seconds ago only if I can recall what my dog looked like five seconds ago. Similarly, I can interpret the series of my impressions as being connected in a causal sequence only if they can be recalled. “As memory alone acquaints us with the continuance and extent of this succession of perceptions, ’tis to be consider’d, upon that account chiefly, as the source of personal identity”.
Locke and Hume agree on this much. The notion of identity (whether personal, biological, or material) is a useful grammatical convention that we use to describe and understand the series of our ever-changing sense-impressions, though in reality, it cannot be found in any of our impressions, and therefore, does not constitute a legitimate idea (concept).