Well, I'm just learning all sorts of things lately. A while back I wrote down some thoughts about Transcendental Empiricism. I mentioned in passing that this was to be distinguished from the simple empiricism of David Hume. Attributing this view to Hume was based on probably a handful of paragraphs I read in college. It's the kind of cartoon version of Hume you may have encountered where he says something like, "Correlation is not causation. All we can ever know is that every time A happens then B seems to happen, but we can't ever know that A caused B". This seems like a simplistically empirical idea because it implies some subject who comes fully furnished with a concept of what causality would be. The more complex and interesting (and still empirical) question would be to ask how we got this idea of causality to begin with. Simple empiricism treats the subject as if it had many elaborate and fully formed theories of what the world might well be like, but happened to have its eyes closed. Maybe the world is filled with red balloons, or exclusively sausages, or very small rocks that float. All of these are a priori equally possible. And then the subject opens its eyes, takes in the data, and voilá, turns out the answer was #9 on the list: bottlecaps. This sort of empiricism starts with too many non-empirical assumptions. It's only empirical about the very last point of reality; it just won't let you deduce absolutely everything from first principles. But it lets you get 99% of the way there with your eyes closed.
Turns out Hume wasn't such a simple empiricist after all. Now that we've actually encountered him for the first time in D&R, I've put a little time into reading more about what he actually said. I still haven't really read any Hume, mind you, but I have looked at this useful page from the Stanford Encyclopedia of Philosophy, as well as the essay on Hume included in Pure Immanence. His discussion of the idea of causality, in particular, seems to have been much more subtle than I realized. It connects to both Darwinism and the version of atomism we saw in Whitehead. It can help us understand the importance of habit in this first section of Chapter 2. And it's just plain interesting in its own right. Let me start the discussion with a summary of some of the key points in that Stanford entry.
Hume thinks perception can be divided into two categories, impressions and ideas. Impressions include the original and primary sense data we get from our eyes, etc ... as well as the secondary or reflective feelings and desires we experience all day long. Ideas seems to be basically the less immediate re-presentations of the original impressions; things like the idea of an object, memories, daydream images, etc ...
He uses perception to designate any mental content whatsoever, and divides perceptions into two categories, impressions and ideas.
Impressions include sensations as well as desires, passions, and emotions. Ideas are "the faint images of these in thinking and reasoning" (T 1.1.1.1/1). He thinks everyone will recognize his distinction, since everyone is aware of the difference between feeling and thinking. It is the difference between feeling the pain of your present sunburn and recalling last year's sunburn.
Hume distinguishes two kinds of impressions: impressions of sensation, or original impressions, and impressions of reflection, or secondary impressions. Impressions of sensation include the feelings we get from our five senses as well as pains and pleasures, all of which arise in us "originally, from unknown causes" (T 1.1.2.1/7). He calls them original because trying to determine their ultimate causes would take us beyond anything we can experience. Any intelligible investigation must stop with them.
Impressions of reflection include desires, emotions, passions, and sentiments. They are essentially reactions or responses to ideas, which is why he calls them secondary. Your memories of last year's sunburn are ideas, copies of the original impressions you had when the sunburn occurred. Recalling those ideas causes you to fear that you'll get another sunburn this year, to hope that you won't, and to want to take proper precautions to avoid overexposure to the sun.
At first, the contrast of the terms "impressions" and "ideas" might lead you to think along the lines of a simple empiricism where the impressions are just the input of sense data and the ideas are somehow the program manipulating that data and relating the impressions -- as if the mind operated on the data it gets from the world, thereby linking input data to output action. But that's not what's going on here. In Hume's classification, both types of impressions, along with our ideas, are just so much data of experience. Much like we saw with Whitehead, the empirical givens of our perception are not limited to simple sensory impressions like "flashing red blob and high-pitched noise", but include ideas like "siren", and reflective impressions or sentiments like, "oh shit, let's eat those before the cop pulls up". All of these things are the atoms of our experience. The ideas aren't ways of connecting sense impression atoms. In fact, Hume will go on to assert that each simple idea is correlated to a simple impression, as if the two flickered past in parallel processions, rather than ideas intervening between sensations to connect them.
In the Treatise, Hume qualifies his claim that our ideas are copies of our impressions, making clear that it applies only to the relation between simple ideas and simple impressions. He offers this "general proposition", usually called the Copy Principle, as his "first principle … in the science of human nature":
All our simple ideas in their first appearance are deriv'd from simple impressions, which are correspondent to them, and which they exactly represent. (T 1.1.1.7/4)
Deleuze points out in his essay on Hume that the fears and wants and hopes that constitute our secondary impressions are likewise not programs for connecting primary sense datums. They are impressions of movement or the relationship between other ideas and impressions, but they don't themselves constitute that link. We are moved from the impression of a hot day to the idea of the pain of last summer's sunburn to the impression of fear of pulling that boneheaded move again. But these just parade by us as so many distinct perceptions.
So how does Hume think ideas or impressions get linked up then? Through force of habit. This is where his deep empiricism lies. Neither impressions nor ideas have any inherent link between them. They are the atomic units of perception that get linked only through our actual experience in the world. Deleuze calls this Hume's assertion that "relations are external to their terms", regardless of whether the relations are between ideas or between impressions.
Hume's originality -- or one of Hume's originalities -- comes from the force with which he asserts that relations are external to their terms. We can understand such a thesis only in contrast to the entire endeavour of philosophy as rationalism and its attempt to reduce the paradox of relations: either by finding a way of making relations internal to their own terms or by finding a deeper and more comprehensive term to which the relation would itself be internal. "Peter is smaller than Paul": How can we make of this relation something internal to Peter, or to Paul, or to their concept, or to the whole they form, or to the Idea in which they participate? How can we overcome the irreducible exteriority of relations? Empiricism has always fought for the exteriority of relations. But in a certain way, its position on this remained obscured by the problem of the origin of knowledge or of ideas, according to which everything finds its origin in the sensible and in the operations of a mind upon the sensible
Simple empiricism says that we have to base our knowledge of the world on sense data instead of just pure rational speculation. But it assumes that there is a mind around with a particular a priori structure that naturally relates one bit of sense data to another. In other words, simple empiricism says that relations are exterior to the sense data terms, but still interior to a mind. It postulates a mind that has a built in program of ideas (like, say, the idea of causality or the idea of similarity) that relate sense data as variables inside some equation. Hume is going to go a step further and question how the mind got this ability to relate terms. How and why do we move from one impression to another? But also, how and why do we move from one idea to another?
Hume effects an inversion that would take empiricism to a higher power: if ideas contain nothing other and nothing more than what is contained in sensory impressions, it is precisely because relations are external and heterogenous to their terms -- impressions or ideas. Thus the difference isn't between ideas and impressions but between two sorts of impressions or ideas: impressions or ideas of terms, and impressions or ideas of relations. The real empiricist world is thereby laid out for the first time to the fullest: it is a world of exteriority, a world in which thought itself exists in a fundamental relationship with the Outside, a world in which terms are veritable atoms and relations are veritable external passages; a world in which the conjunction "and" dethrones the interiority of the verb "is"; a harlequin world of multicolored patterns and non-totalizable fragments where communication takes place through external relations. Hume's thought is built up in a double way: through the atomism that shows how ideas or sensory impression refer to punctual minima producing time and space; and through the associationism that shows how relations are established between these terms, always external to them, and dependent on other principles.
I almost want to rephrase Hume's categories here to say that ideas are really just a kind of impression; ideas are impressions too. This seems to me to draw out the deeper empiricism we're talking about because it emphasizes that fact that the ideas in our mind have no deep and special place in the universe of "things" we experience. In particular, they are not some sort of privileged force for linking and organizing those things, they are just more things themselves. Empiricism means accepting that everything we are aware of in perception is real, and not disqualifying some things as merely derived from others by an equation that transforms an identity from one side to the other. Elsewhere Deleuze says that, "I have always felt that I am an empiricist, that is, a pluralist". This is why empiricism insists on the exteriority of relations, to preserve the independent reality of each of the things we experience, to not reduce one thing to another. Which conversely means that every relation we experience as an idea or impression is like a new creation -- "is" gets transformed into "and". This idea and then that idea is actually a new idea. Later this conjunction may be repeated, we may find habits and patterns in experience, but for an empiricist, these forms are more like a reappearance, a new production of the "same". I think that's the message of this comment on Samuel Butler:
... 'for even the corn in the fields grows upon a superstitious basis as to its own existence, and only turns the earth and moisture into wheat through the conceit of its own ability to do so, without which faith it were powerless ...'. Only an empiricist can happily risk such formulae.
There's no form of wheat that pre-exists the conjunction of elements that constitute it. Which means that the wheat simultaneously comes from "Outside" those elements and simultaneously creates itself as a thing -- it's hard to non-paradoxically describe this kind of circular self-positing conjunction or relation.
Naturally, we want to know more about this "Outside" and about how relations are created between atoms that are not internal to the atoms, nor to some larger form or concept that pre-exists their combination. Hume has an answer to this question; there are principles of association that operate like gravity to draw ideas together.
Although we are capable of separating and combining our simple ideas as we please, there is, nevertheless, a regular order to our thoughts. If ideas occurred to us completely randomly, so that all our thoughts were "loose and unconnected", we wouldn't be able to think coherently (T 1.1.4.1/10).
This suggests that there is a secret tie or union among particular ideas, which causes the mind to conjoin them more frequently, and makes the one, upon its appearance, introduce the other. (Abstract 35)
Hume explains this "tie or union" in terms of the mind's natural ability to associate certain ideas. Association is not "an inseparable connexion", but rather "a gentle force, which commonly prevails", by means of which one idea naturally introduces another (T 1.1.4.1/10).
Hume identifies three principles of association: resemblance, contiguity in time and place, and causation.
Like gravitational attraction, the associative principles are original, and so can't be explained further. Although the associative principles' "effects are everywhere conspicuous" their causes "are mostly unknown, and must be resolv'd into original qualities of human nature, which I pretend not to explain". Accordingly, we should curb any "intemperate desire" to account further for them, for doing so would take us illegitimately beyond the bounds of experience (T 1.1.4.6/12–13).
Hume doesn't try to explain why we associate ideas as we do. He is interested only in establishing that, as a matter of fact, we do associate ideas in these ways.
Atomic ideas get associated because they exhibit resemblance, or continuity, or causation. These principles together constitute the nature of the human mind. This explanation sounds okay at first, but feels more disappointing the more you think about it. We move from one idea to another that resembles it, from a picture to the person it looks like. But wait, how did the mind decide that these two ideas resembled one another enough to permit a connection? It seems like we're begging the question. We're still not explaining the cause of the attraction between the ideas, just the fact that they are attracted. Deleuze points out that this disappointment reveals our misunderstanding of Hume's empiricism.
What is a relation? It is what makes us pass from a given impression or ideas to the idea of something that is not presently given. For example, I think of something "similar" ... When I see a picture of Peter, I think of Peter, who isn't there. One would look in vain in the given term for the reason for this passage. The relation is itself the effect of the so-called principles of association, contiguity, resemblance, and causality, all of which constitute, precisely, a human nature. Human nature means that what is universal or constant in the human mind is never one idea or another as a term but only the ways of passing from one particular idea to another. Hume, in this sense, will devote himself to the concerted destruction of the three great terminal ideas of metaphysics: the Self, the World, and God. And yet at first Hume's thesis seems disappointing: what is the advantage of explaining relations by principles of human nature, which are principles of association that seem just another way of designating relations? But this disappointment derives from a misunderstanding of the problem, for the problem is not of causes, but of the way relations function as effects of those causes and the practical conditions of this functioning.
The mind is actually a passive sort of machine in Hume's theory. It's not actively associating two ideas. It's as if some other force outside the mind caused the attraction of those ideas, and the mind merely follows that link. The relations our mind makes between things are not the cause of their association, but rather that effect of the way our mind is caused to work. If we let the mind be the cause of the principles of association, if we allow that it invents these connections itself, then we end up explaining the relations we experience by saying that we experience relations. Turns out this circularity is actually key to Hume's account of why we conceive relations like causality, but in an unexpected way.
Causal inferences are the only way we can go beyond the evidence of our senses and memories. In making them, we suppose there is some connection between present facts and what we infer from them. But what is this connection? How is it established?
In the past, taking aspirin has relieved my headaches, so I believe that taking aspirin will relieve the headache I'm having now. But my inference is based on the aspirin's superficial sensible qualities, which have nothing to do with headache relief. Even if I assume that the aspirin has "secret powers" that are doing the heavy lifting in relieving my headache, they can't be the basis of my inference, since these "secret powers" are unknown.
Nonetheless, Hume observes, "we always presume, when we see like sensible qualities, that they have like secret powers, and expect that effects, similar to those we have experienced, will follow from them" (EHU 4.2.16/33). Since we neither intuit nor infer a priori that similar objects have similar secret powers, our presumption must be based in some way on our experience.
But our past experience only gives us information about objects as they were when we experienced them, and our present experience only tells us about objects we are experiencing now. Causal inferences, however, do not just record our past and present experiences. They extend or project what we have gathered from experience to other objects in the future. Since it is not necessarily true that an object with the same sensible qualities will have the same secret powers that past objects with those sensible qualities had, how do we project those experiences into the future, to other objects that may only appear similar to those we've previously experienced?
Hume thinks we can get a handle on this question by considering two clearly different propositions:
(1) I've found that headache relief has always followed my taking aspirin;
and
(2) Taking aspirin similar to the ones I've taken in the past will relieve my present headache.
There is no question that "the one proposition may be justly inferred from the other", and that "it is always inferred". But since their connection obviously isn't intuitive, Hume challenges us to produce the "chain of reasoning" that takes us from propositions like (1) to propositions like (2) (EHU 4.2.16/34)
(1) summarizes my past experience, while (2) predicts what will happen in the immediate future. The chain of reasoning I need must show me how my past experience is relevant to my future experience. I need some further proposition or propositions that will establish an appropriate link or connection between past and future, and take me from (1) to (2) using either demonstrative reasoning, concerning relations of ideas, or probable reasoning, concerning matters of fact.
Hume thinks it is evident that demonstrative reasoning can't bridge the gap between (1) and (2). However unlikely it may be, we can always intelligibly conceive of a change in the course of nature. Even though aspirin relieved my previous headaches, there's no contradiction in supposing that it won't relieve the one I'm having now, so the supposition of a change in the course of nature can't be proven false by any reasoning concerning relations of ideas.
That leaves probable reasoning. Hume argues that there is no probable reasoning that can provide a just inference from past to future. Any attempt to infer (2) from (1) by a probable inference will be viciously circular—it will involve supposing what we are trying to prove.
Hume spells out the circularity this way. Any reasoning that takes us from (1) to (2) must employ some connecting principle that connects the past with the future. Since one thing that keeps us from moving directly from past to future is the possibility that the course of nature might change, it seems plausible to think that the connecting principle we need will be one that will assure us that nature is uniform—that the course of nature won't change—something like this Uniformity Principle:
[UP] The future will be like the past.
Adopting [UP] will indeed allow us to go from (1) to (2). But before we can use it to establish that our causal inferences are determined by reason, we need to determine our basis for adopting it. [UP] is clearly not intuitive, nor is it demonstrable, as Hume has already pointed out, so only probable arguments could establish it. But to attempt to establish [UP] this way would be to try to establish probable arguments using probable arguments, which will eventually include [UP] itself.
So we can't reason our way into justifying why we experience a relation of causality. It's an effect of the way our minds are built, caused by something other than the mind. I think Hume believes the same of the other principles of association, but this is particularly clear in the case of causality, for reasons Deleuze points out.
It is special because it doesn't simply go from a given term to the idea of something that isn't presently given. Causality requires that I go from something that is given to me to the idea of something that has never been given to me, that isn't even giveable in experience. For example, based on some signs in a book, I believe that Caesar lived. When I see the sun rise, I say that it will rise tomorrow; having seen water boil at 100 degrees, I say that it necessarily boils at 100 degrees. Yet expression such as "tomorrow", "always", "necessarily", convey something that cannot be given in experience: tomorrow isn't given without becoming today, without ceasing to be tomorrow, and all experience is experience of a contingent particular. In other words, causality is a relation according to which I go beyond the given; I say more than what is given or giveable -- in short, I infer and I believe, I expect that ...
If the mind didn't invent causality as a principle of association and doesn't control it (but is controlled by it) then where does it come from? What causes our belief in causality? Hume's response here is again habit. But there's a kind of subtle twist here. Because now we are not (we cannot) be talking about the habits of the world, or the patterns of our sense experience where A is followed by B. We cannot experience causality directly. We are referring to the habits of our mind where the appearance of A leads to the idea that B will appear, because it is inevitably caused by A.
Since we're determined—caused—to make causal inferences, then if they aren't "determin'd by reason", there must be "some principle of equal weight and authority" that leads us to make them. Hume maintains that this principle is custom or habit:
whenever the repetition of any particular act or operation produces a propensity to renew the same act or operation … we always say, that this propensity is the effect of Custom. (EHU 5.1.5/43)
It is therefore custom, not reason, which "determines the mind … to suppose the future conformable to the past" (Abstract 16). But even though we have located the principle, it is important to see that this isn't a new principle by which our minds operate. Custom and habit are general names for the principles of association.
Hume describes their operation as a causal process: custom or habit is the cause of the particular propensity you form after your repeated experiences of the constant conjunction of smoke and fire. Causation is the operative associative principle here, since it is the only one of those principles that can take us beyond our senses and memories.
The habit in question here is the direct experience of the constant conjunction of two terms in a relation. This is our experience of the belief in causality, as a sort of force operating on our minds. As a belief or expectation, it seems to fit under what Hume described at the beginning as the secondary impressions. We've experienced a repetition of the conjunction of smoke and fire, which leads us to experience our mind moving naturally from smoke to fire in the form of the belief that one is the cause of the other. This statement might seem a little obvious till you realize that Hume is actually saying that these two connections each occur independently. The world gives us a series of external impressions of smoke-then-fire, smoke-then-fire. And then our minds, as a result of being built the way they are, presuming the uniformity of nature, give us an internal impression of the belief that fire causes smoke. The two run on parallel tracks, the external impressions connected by habits of the world, and the internal impressions connected by habits of our mind.
But how does an idea come to be conceived in such a manner that it constitutes a belief?
Hume's explanation is that as I become accustomed to aspirin's relieving my headaches, I develop a propensity—a tendency—to expect headache relief to follow taking aspirin. The propensity is due to the associative bond that my repeated experiences of taking aspirin and headache relief have formed. My present impressions of taking an aspirin are as forceful and vivid as anything could be, and some of their force and vivacity transfers across the associative path to the idea of headache relief, enlivening it with enough force and vivacity to give it the "strength and solidity" that constitutes belief.
Since I don't know how aspirin relieves headaches, it is fortunate that there is "a kind of pre-established harmony between the course of nature and the succession of our ideas" that teaches me to take aspirin when I have a headache. Custom, Hume maintains, in language that anticipates and influenced Darwin,
is that principle by which this correspondence has been effected; so necessary to the subsistence of our species, and the regulation of our conduct, in every circumstance of human life. (EHU 5.2.21/55)
It's interesting to again end up back at Darwinism. The world has its habits, and our minds have theirs. If the two aren't mutually adjusted, we won't be around for long. Clearly, we don't now think this correlation happens because of some pre-established harmony, but through learning, or adaptation in the broader case. This is how we get one set of connections to match up with another, how we learn to swim. It's not a theoretical question knowing how to swim. It's a pragmatic question of believing that we can.
Deleuze sums the situation up in this passage of his Pure Immanence essay, which clearly provides the starting point for Chapter 2 of D&R:
The functioning of the causal relationship can then be explained as follows: as similar cases are observed (all the times I have seen that a follows or accompanies b), they fuse in the imagination, while remaining distinct and separate from each other in the understanding. This property of fusion in the imagination constitutes habit (I expect ...), at the same time as the distinction in the understanding tailors belief to the calculus of observed cases (probability as calculus of degrees of belief). The principle of habit as fusion of similar cases in the imagination and the principle of experience as observation of distinct cases in the understanding thus combine to produce both the relation and the inference that follows from the relation (belief), through which causality functions.
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