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Representative Realism, Phenomenalism, and "Physical-Talk"

It has been over a month since my last post, and for this I apologize. I doubt if I will be posting any more frequently in the near future as I am getting married on August 2 and moving from Philadelphia to Los Angeles immediately after the honeymoon. I'm sure the Internet will get by just fine without me.

Right now, however, I do have a bit of time, and I want to discuss an argument for phenomenalism about the physical world. When I wrote a while back about the idealist strategy, I said that the second step was to "argue that our physical statements - both ordinary statements about physical objects and statements about the discipline of physics - are best construed as talking about perception." What I want to do here is to unpack this statement. First, let's examine what the argument is supposed to do, and then we'll look at the argument as it appears in a brief section of Berkeley's Three Dialogues.

This piece of the argument is a reductio against representative realism. The first step of the idealist strategy is supposed to eliminate direct realism (the view that the very same things we experience in sense perception exist mind-independently and are known by us directly). I will assume this has already been accomplished. This leaves representative realism, the view that our perception are representations of mind-independent reality.

There are effectively two flavors of representative realism, both of which are, I think, fairly popular among philosophers today. The first is causal representation, which claims that our mental states come to represent things in the world in virtue of having been caused by them. This view has been supported by Fred Dretske. It has some problems which many philosophers have tried to shore up by a variety of strategies. The most important problem for it is the possibility of misrepresentation - e.g., how can we mistake a cow for a horse (from a distance, in the dark) if horse-thoughts represent horses precisely because they are caused by horses (but this one was caused by a cow)? I will not dwell on this objection, but there is a vast literature on it.

The second flavor is primitive or mysterian representation. This view takes representation as a primitive -i.e. one of the fundamental concepts of the theory, which does not admit of further analysis. The main objections to this view have to do with (1) whether you can adequately define the formal properties of representation in a coherent fashion, and (2) whether representation makes a good primitive. The latter is probably the most important, but the question of what makes something a good or bad primitive is extremely complex.

For the idealist's purposes, what matters is that when I perceive a table, there are two things: the 'real' table, and my perception or representation of the table. These are not the same thing. This much is conceded by the representative realist. It is customary to refer to the mental tokening which represents the table as a 'table', after the way we discuss words in philosophy of language, but this is going to get really confusing in this particular argument, so from here on out I will use table_i to refer to mind-independent table objects, table_m to refer to mind-dependent table-representations, and 'table' to refer to the English word spelled t-a-b-l-e. (I'm not sure how much less confusing that will be, but I'm hoping it won't be too difficult to follow.)

Suppose the phenomenalist grants, for the sake of argument, that there is such a thing as a table_i and that, under ordinary circumstances, there is a one-to-one correlation between tables_i and tables_m. Now listen to Berkeley:

Ask the gardener, why he thinks yonder cherry-tree exists in the garden, and he shall tell you, because he sees and feels it; in a word, because he perceives it by his senses. Ask him, why he thinks an orange-tree not to be there, and he shall tell you, because he does not perceive it. What he perceives by sense, that he terms a real being, and saith it is, or exists; but that which is not perceivable, the same, he saith, hath no being. (Three Dialogues Between Hylas and Philonous, 234)

The disagreement between the Hylas and Philonous at this point is that Hylas supposes that 'cherry-tree' refers to the cherry-tree_i, whereas Philonous believes it refers to the cherry-tree_m. The argument, in other words, is that representative realism provides a poor analysis of "physical-talk". By "physical-talk" I mean the ordinary statements of non-philosophers about physical things, whether in the context of physics or everyday life.

The realist needs to argue that 'table' refers to the table_i. Now, Berkeley's principal target is Locke, and this argument immediately overcomes Locke. Consider:

Let us then suppose the mind to be, as we say, white paper, void of all characters, without any ideas; how comes it to be furnished? ... To this I answer, in one word, from experience ... Our observation employed either about external, sensible objects; or about the internal operations of our minds, perceived and reflected on by ourselves, is that, which supplies our understandings with all the materials of thinking. (Essay Concerning Human Understanding, 2.1.2, emphasis original)

Locke isn't a representative realist. Rather, he holds a hybrid view according to which some properties ('primary qualities') are perceived directly and others ('secondary qualities') mediated by a representation. If direct realism falls (and we are assuming that it has already fallen), then no object can be both external and sensible, so Locke cannot claim that our "physical-talk" refers to external objects.

More recently the cause has been taken up by Kripke:

When I refer to heat, I refer not to an internal sensation that someone may have, but to an external phenomenon which we perceive through the sense of feeling; it produces a characteristic sensation which we call the sensation of heat. Heat is the motion of molecules. (Naming and Necessity, 129)

Now, recall that under Kripke's theory of reference, an object or natural kind is named by an initial 'baptism' in which someone points to it (literally or figuratively) and gives it a name. The name is subsequently passed on by the speaker community from one person to another. So, under Kripke's theory, how would 'heat' acquire the referent heat_i? Nobody can point to heat_i, because nobody perceives heat_i ("molecular motion"), we all perceive heat_m ("the sensation of heat"). Kripke says: "In the case of a natural phenomenon perceptible to the senses, the way the reference is picked out is simple: 'Heat = that which is sensed by sensation S'." (ibid. 136) This, however, is simply a statement, not an argument. To say "that which is sensed by sensation S" is the same as to say "that which is represented by sensation S".

The phenomenalist wants to argue that this is not a good analysis of 'heat'. Heat_i isn't a sensation. It can't be felt. If you ask the gardener to define 'cherry tree', he will describe a cherry tree_m: something that is seen, felt, smelled, etc. If you ask an ordinary person to define 'table', she will describe something that looks and feels (and therefore is) flat, that you can set objects on, etc. No one who has not been reading Aristotle, Locke, and friends will say anything about a "material substratum." No one will say "the object that causes my table perceptions." The table doesn't cause something to feel flat, the table itself feels flat.

Physicalists tend to be very adamant about believing only in the objects of their senses, but then begin describing things that can't be sensed at all, and claiming that those are the objects of their senses. If the phenomenalist can make this case that physical-talk is best understood as referring to objects_m, then matter will be superfluous to metaphysical explanations of the world we experience. Furthermore, if Kripke's "pass-through" reference fails, then his theory will make it impossible to refer to objects_i, for the same reason it is impossible for Putnam's brains in vats to wonder whether they are brains in vats.

What Does Bayesian Epistemology Have To Do With Probabilities?

The answer to the question in the title of this post may seem obvious (after all, isn't Bayesianism all about probabilities?), but I think that the long discussion that followed Lauren's post on van Fraassen's objection to Bayesianism from quantum mechanics shows that it isn't clear at all - or at least, that it wasn't clear to either of us as we were discussing the issue. I think that I now understand why. In this post, I'm going to give three answers to this question, which I will call The Primitivist Account (P), The Kripkean Possible Worlds Account (KPW), and the Lewisian Possible Worlds Account (LPW). This post will discuss what each view means, and where vagueness enters each account. I will also be identifying three crucial problems with (P) and showing how each of the other views answers these difficulties.

Here are brief definitions of each view, and how each one relates subjective degrees of rational confidence to probabilities (I will explain in more depth later).

• (P) takes subjective degrees of rational confidence as primitive. There is no state space for degrees of rational confidence, because they aren't probabilities.
• (KPW) takes subjective degrees of rational confidence to be actual probabilities over the state space of all epistemically possible worlds, where the epistemically possible worlds are formal constructions that may or may not be objectively possible.
• (LPW) takes subjective degrees of rational confidence to be actual probabilities over the state space of the subset of the really possible worlds which are epistemically accessible.

Part of the reason for the previous confusion is that I was more or less assuming (P), and I think that Lauren had noticed some serious problems with it. First, a word on the reason for my assumption, and then I will try to state Lauren's objections.

(P) may be the dominant interpretation of Bayesianism. I don't really know. But there is good reason why someone reading the literature might think it's the dominant interpretation: it maps especially well to how Bayesian philosophers actually apply Bayesianism. Most philosophers who apply Bayesian reasoning (myself included) do it by simply making up numbers that are supposed to represent their degrees of confidence. Where do these numbers come from? We simply observe that we have varying degrees of confidence about different beliefs, and map these degrees of confidence to the real numbers between 0 and 1. Vagueness comes in from the fact that we don't have mathematically precise degrees of confidence, and our numbers are simply made up from our imprecise degrees of confidence, rather than computed somehow.

Now, as I have said, I believe that three important questions came out in our previous discussion which this theory leaves unanswered:

1. Why should we suppose that we can use the math of probability theory in dealing with degrees of rational confidence?
2. The math of probability theory is generally interpreted in terms of sets called state spaces, but, ex hypothesi, degrees of rational confidence, not being probabilities, have no state spaces. What, then, does the math mean?
3. Why should we suppose that when an occurence has a well defined objective probabilty, our subjective degree of rational confidence should be assigned a value equal to its probability?

(P) does not answer these questions. This is, of course, to be expected from a theory called "primitivism," but I think the third question is particularly problematic. In the previous discussion, it was van Fraassen's assumption that we should do this very thing that brought up the issue. However, Bayesianism really needs these principles. Is it possible to provide an analysis of degrees of rational confidence that adequately answers these questions? (KPW) and (LPW) will attempt this very thing.

(KPW) is inspired by Kripke's treatment of possible worlds in terms of state spaces in the 1980 preface to Naming and Necessity, pp. 15-20. Kripke here argues that possible worlds are the same sorts of things as the "states" used in school probability theory, the difference being that possible worlds are maximally specific. Now, consider a view according to which the state space of Bayesian reasoning is the space of all epistemically possible worlds - that is, all the world-states (which are abstractions just like dice-states) which might for all we know be actual. Note that not all of these may be really possible. For instance, the Anselmian God either exists or does not exist, with logical necessity, but his existence and non-existence may both be epistemically possible for a particular person. So, when we say that we have subjective degree of confidence .5 for a given proposition, we are saying that that proposition holds in half of all epistemically possible worlds.

This view will be helped by Lewis's observation about the relationship between propositions and possible worlds: namely, that every proposition picks out a set of possible worlds, the worlds in which it obtains. (Lewis wants this to be a reductive analysis of propositions, but we need not do that.) So, consider any given proposition you believe. There is a set of possible worlds in which that proposition obtains. The set of epistemically possible worlds (for you) is the intersection of the sets for all the propositions you believe.

The (KPW) answer to question (1) has already been given - Bayesian degrees of confidence are probabilities. Let's proceed to give an interpretation of the math on (KPW).

Bayes' theorem is a relation between an initial probability - a probability over some state space S - and a conditional probability - a probability over some subset S' of S. Usually, we consider some proposition p and some evidence e. We already have assigned a particular degree of confidence to p and we want to adjust our confidence in light of learning the new evidence e. We use Bayes's theorem to calculate P(p|e). What has happened here? The new evidence e has eliminated certain formerly epistemically possible worlds - namely, all the worlds according to which ~e. In order to computer P(p|e) we have to know something about the relationship between p and e. In particular, we have to know P(e|p), P(p) and P(e) (all of them over the initial state space S). This involves knowing how many of our epistemically possible worlds certain conditions obtain in.

The (KPW) answer to question (3) should now be quite clear. Probabilities for events like dice rolls are, on this view, actually just special cases of degrees of subjective confidence. Why is there a 1/6 probability of a single die rolling 1? Because in 1/6 of all epistemically possible worlds it will land 1. (We should think of these world-states as covering the whole history of the world, so future events can be handled the same as past or present events.) In our school probability exercises, we simplify the case by supposing there are only 6 worlds. In fact, there are 6 sets of worlds. We know that the worlds will divide more or less evenly (we assume we know with certainty that the die will be rolled), because most of the propositions we are uncertain about vary independently of the result of the die roll. The ones that don't vary independently (e.g. propositions stating that the die is unfair in some particular way) are, for all we know, as likely to favor one side of the die as another.

Vagueness enters (KPW) by virtue of the fact that the worlds are created by us. They don't exist objectively. As such, there is vagueness as to how many worlds there are, and there is vagueness as to whether certain propositions are true in certain worlds. These things are simply not fully defined. We should nevertheless be able to fix upper and lower bounds by considering all of the possible resolutions of the vagueness (actually, we can probably do better by figuring out in advance which resolutions will lead to high values, and which to low values). In practice, however, we do something more like the die role case: we eliminate all the propositions that vary (more or less) independently (as far as we know) of the propositions under consideration, to divide the epistemically possible worlds into sets, and then consider each set as a single underspecified world.

(LPW) is very similar to (KPW) in its answers to the three questions. (LPW) holds that we are talking about real possible worlds, which are epistemically accessible - that is, which might, for all we know, be the world we're in. Vagueness on (LPW) is different. Because the worlds are fully defined and there is an objective truth about how many there are, there is only one source of vagueness properly so-called: vagueness about whether a given world is epistemically accessible. However, there is also second-order uncertainty - uncertainty about whether a certain world is genuinely possible, or whether a given proposition obtains in a certain world.

These two theories improve on (P) by providing explanations for why we use Bayesian reasoning the way we do, and why it works like probability theory at all. They also allow us to define our degrees of confidence much more clearly.