Before I go on to discuss what Hume has to say about the common experience of perceiving objects that change over time, it occurs to me that I should repeat, and emphasize, something I said at the very beginning of this explication but have not returned to, namely that Hume is a Direct Realist. Someone might after all be tempted to say, “There is no problem about treating a multiplicity of impressions as impressions of identically the same object because they are, after all, all caused by the same object. That in fact is just why we say of them that they are perceptions of identically the same object. [And at this point the speaker interposes his or her favorite theory of substantial identity, or whatever.] But Hume rejects this account, for, as I indicated, he argues that we all [children and peasants and the rest of us in our non-philosophical moments] take what we perceive to be the objects themselves, not to be representations of objects or copies of objects. And since I can never step outside my consciousness, as it were, and observe both the object and myself from some neutral standpoint, in order to ascertain their causal relationship to one another, I can arrive at a causal theory of perception only by First developing an ordinary unreflective identification of objects with my perceptions, and Then recognizing the puzzles and problems with that identification, and retreating to a causal theory to sort things out. Thus the causal realist story is parasitic on the original direct realist beliefs, and it is they that must be explained or accounted for in their own terms, before I ever advance a causal realist story about perception.
Hume’s term for the process we have been describing, in virtue of which I impute identity to a multiplicity of resembling impressions, first when they are continuous, then even if they are gappy, is constancy. But constancy alone cannot account for my belief in the continued and independent existence of objects. To explain that belief, I must also appeal to a second characteristic of my perceptions, which he labels coherence. It is quite common for me to find, putting it naively and unphilosophically, that objects change over time. To use Hume’s own example, not only do I have only a gappy series of perceptions of the fire in my grate, inasmuch as I do not stare fixedly at it but only notice it intermittently; it is also the case that frequently I leave my closet [his word for a study] and return to find that in the interim, the fire has burned down, leaving only ashes in the grate. Nevertheless, I readily suppose that the ashes are identical with the fire, but are simply a later stage of the same object. Clearly, this supposition is in multiple ways unsupported by any rational argument. What leads me to this familiar conclusion?
Hume’s answer is as follows: I have repeatedly observed my fire to burn down to ashes, looking at it all the while. This constant conjunction of resembling impressions triggers my innate propensity to associate these perceptions together in the manner I have already explained, leading me to form a series of causal beliefs. In order to preserve the coherence and order of my experience, I posit an unobserved sequence of causes and effects htat connect up my perception of the fire in my grate before I leave my study with the perception of the ashes in the grate after I return. I flesh out my experience by these quite unjustifiable but irresistible positings. Furthermore, the action of the mind in running over a series of causes and effects resembles the action of the mind in running over a series of perfectly resembling impressions, and so my mind associates them together, and imputes to the causal series the identity that it has previously imputed to the series of perfectly resembling impressions.
Thus, starting from a perceptual experience that is in actual fact quite fluid, changeable, gappy, and inconstant, I repeatedly fill in the gaps, posit unperceived impressions, confuse two different but similar actions of the mind, all in the service of forming and then reposing belief in the idea of a coherent, orderly, predictable, manageable experienced world of objects.
Among the many questions that this account might provoke, there is one to which Hume gives a quite striking answer, one whose philosophical significance is very great especially for someone like myself who is constantly reading Hume with an eye to the theories of Kant. Here is Hume’s way of posing the question, followed by his answer:
“ ‘Tis certain, that almost all mankind, and even philosophers themselves, for the greatest part of their lives, take their perceptions to be their only objects, and suppose, that the very being, which is intimately present to the mind, is the real body or material existence. ‘Tis also certain, that this very perception or object is suppos’d to have a continu’d uninterrupted being, and neither is to be annihilated by our absence, nor to be brought into existence by our presence. When we are absent from it, we say it still exists, but that we do not feel, we do not see it. When we are present, we say we feel, or see it…. How can we satisfy ourselves in supposing a perception to be absent from the mind without being annihilated[?] …
“...As to [this] question, we may observe that what we call a mind is nothing but a heap or collection of different perceptions, united together by certain relations, and suppos’d, tho’ falsely, to be endow’d with a perfect simplicity and identity. Now as every perception is distinguishable from another, and may be consider’d as separately existent; it evidently follows, that there is no absurdity in separating any particular perception from the mind; that is, in breaking off all its relations with that connected mass of perceptions, which constitute a thinking being.”
To any of you followed my tutorial on The Critique of Pure Reason before embarking with me on this consideration of the philosophy of David Hume, I can say that this is the precise point at which Kant breaks with Hume. Kant insists on the unity of consciousness, and his analysis reveals that we cannot even bring this mass of perceptions -- what Kant calls “the manifold of sensibility” – to the unity of consciousness unless a process of synthesis has been gone through, a “reproduction in imagination according to a rule.” It is that new step in the argument that allows Kant to conclude that the systematic organization of the experienced perceptions constitutes a world order – and that our belief in that world order is not a mere habit, but in fact is deducible from the unity of consciousness itself.
Well, this is very hard for me, and I imagine hard for you as well, so I shall stop here until tomorrow.