Sider, structure, reduction, and knowledge first

This is a continuation of yesterday's post. Yesterday I identified what seemed to me to be a problem for the way that Ted Sider wanted to explain why various macro-level things are more privileged—basically, they're said to be more joint-carving. But as I said yesterday, I just don't see that they are.

I suspect, however, that one can get something quite a bit like Sider's picture here if one is willing to add a bit more structure. The prospects for a reasonable purely physical story about chemical objects and properties seem reasonable. It doesn't seem hopeless to try to give a reasonably simple definition of molecule or magnesium or valence in purely physical terms. So if we assume the (absolute) fundamentality of physics, we can run the story Sider wants for why we refer to molecules instead of molecules-or-cucumbers, or even molecules-before-2013-and-regions-of-space-afterwards, because the physical definition of molecule is significantly simpler than these more bizarre properties. (In the former case, a purely physical definition will be insanely complex, as in the case of pig; in the latter, it will still be not insanely complex, but more complex than that for molecule.)

This is basically just a way of expressing the familiar idea that chemistry somehow reduces to, or emerges from, physics. But if we buy into Ted's general ideas, we can add this: it is part of the objective structure of the world that chemical properties are related to physical properties in this way. The 'book of the world' will give us the chemical on top of the physical (and the chemical is objectively privileged over the schmemical).

Now what happens when we go up another level? It's pretty natural to suppose that cell biology relates to chemistry as chemistry does to physics. So --- and here's where the picture I'm describing departs from Ted's --- when adjudicating between which objects we refer to in our discourse about cell biology, objects with reasonably simple definitions in chemical terms --- not physical terms --- are privileged over ones that don't. We don't always go back to the most fundamental; we just go back to the more fundamental domain that is appropriate for the matter at hand. Often, but not always, the simpler definition is the more fundamental theory will correspond to the simpler definition in the ultimately fundamental theory; when it doesn't, I think we should go with the less fundamental one. (It's having a better chemical account that makes a particular referent of 'cell' the preferred one, not having a better physical account.)

The reason I'm interested in this, besides the fact that it's interesting, is that I'm leaning in this kind of a direction as a way of making sense of what the 'knowledge first' attitude is. (Yes, I'm reading metaphysics, but it's in the service of epistemology, I swear!) I understand it as a metaphysical thesis: knowledge is a more fundamental state than has been traditionally recognized. In the terms of this broad way of thinking about theorizing about the world, knowledge shows up at a more fundamental level than one might have thought.  (Compare a 'life first' theorist, who thinks that the attempt to define life in biological terms is a mistake; life's home is really at the chemical level—we need to invoke life to understand, say, combustion.) How early should knowledge appear? Presumably, people could differ about this. If you wanted to, you could think that knowledge was perfectly fundamental; knowledge is as basic as quarks or whatever. You'd oppose any kind of reduction of knowledge to anything. This doesn't sound very plausible, but you could say that if you wanted to. My suspicion is that knowledge will be an important theoretical term from the basics of intentional psychology.

Sider on joint-carving and reference

Humans refer to things sometimes. Ted Sider thinks, with David Lewis, that part of the story for why it is that we refer to some things, rather than other possible things, is that the things we refer to are more natural. This Sider understands as a matter of the primitive structure of the world. To takes one of Ted's examples, Ted's word 'pig' refers to pigs, instead of pigs-before-2011-AD-or-cows-afterwards. And he thinks that general considerations about fundamental structure can yield this intuitive result. Ted writes:

The point may be seen initially by making two strong, crude assumptions about "reasonably joint-carving". Assume first that a notion is reasonably joint-carving iff it has a reasonably simple and nondisjunctive definition in terms of the perfectly joint-carving notions, and second that the perfectly joint-carving notions are those of physics. Then surely no reasonably joint-carving relation that is to play the role of reference could relate a human population to bizarre semantic values. For the bizarre semantic values themselves have no simple basis in the physical, nor do they stand in any physically simple relations to human populations. Given any reduction that does relate us to bizarre semantic values, there is surely some other relation with a simpler basis in the physical that relates us to nonbizarre semantic values. (29)

There is considerable vagueness and imprecision in the notion of "reasonably" simply definitions Ted evokes, but I guess I agree that it's pretty plausible that one couldn't tell a "reasonably simple" story in purely physical terms of how humans are related to bizarre semantic values like pigs-before-2011-AD-or-cows-afterwards. But Ted needs more than just that fact; he needs the comparison. And I guess it just doesn't look very plausible to me that there is a "reasonably simple" definition available in purely physical terms of any of the pieces we need here. By any ordinary standards, a definition of pig --- or human! --- in purely physical terms will be rather unreasonably complex! So I worry that if this is the story about why we don't refer to pigs-before-2011-AD-or-cows-afterwards, it will generalize to show that we don't refer to pigs either. (A related problem; surely it's possible to refer to pigs-before-2011-AD-or-cows-afterwards, right?)

I think this problem persists, even given the less toy version of the theory. He continues the passage above:

The two assumptions of the previous paragraph are undoubtedly too crude, but the point is independent of them. Whether a notion is reasonably joint-carving --- enough to take part in special-science explanations --- has something to do with how it is based in the fundamental. So reference must have the right sort of basis in the fundamental if it's to be explanatory.

But it's just very difficult to say anything halfway reasonably simple about how any of this stuff arises from the fundamental. Things like pigs are just way too far removed from things like electrons. (And presumably, even electrons aren't fundamental anyway.)

More on this theme, and what I think we should say instead, tomorrow.

Sider on epistemic value and nature's joints

Ted Sider thinks that it's epistemically preferable to think in joint-carving terms; this is a way of better matching one's beliefs to the world. While something about that sounds right, I think that some of the the things he says must go too far. He writes, for example, that

[j]oint-carving thought does not have merely instrumental value. It is rather a constitutive aim of the practice of forming beliefs, as constitutive as the more commonly recognized aim of truth. (WtBotW p. 61)

I don't think this can be right. The idea of somebody forming beliefs without any kind of sensitivity or regard for whether they are true is incoherent; this is not so for someone who doesn't care whether her beliefs carve nature at the joints. Suppose one is charged with failing to carve at the joints with her beliefs, and replies flippantly --- so what? --- and maintains her previous beliefs? She might be criticizable on epistemic grounds, but her attitude is comprehensible, even if we do not approve of it. Compare the person who is charged with having false beliefs, and replies in the same way --- indifferently accepting the charge, and continuing to believe as before. This isn't just epistemically vicious; this runs counter to what it is to be a belief. In other words, a truth aim has a better claim to a constitutive connection to belief than a joint-carving aim does.

Here is another difference that should not be overlooked: some instances of non-joint-carving beliefs are absolutely correct to hold. Maybe they're not as good as their joint-carving cousins, but one needn't choose between them. You can believe that the emerald is green and that it is grue. In fact, that's exactly what you should do. And you shouldn't feel at all epistemically deficient for having the latter belief. Compare this to false beliefs: every false belief you have prevents you from having a true one.

Moore-paradoxes show a deep connection between belief and truth; there is a deep incoherence in the idea of accepting: "I believe that p, even though not-p." But there is no corresponding incoherence in "I believe that p, even though the terms in p do not carve at nature's joints."

Whatever epistemic value attaches to joint-carving, it is less central to belief than truth is.

Joint-Carving and Projectability

So this weird thing has been happening to me lately where I think about metaphysics. My current symptom is an attempted negotiation of Ted Sider's recent book, Writing the Book of the World. Ted's Big Idea is that there is objective structure to reality, and that this structure is really important for all kinds of reasons; I find the general picture a pretty attractive one, but I'm rather puzzled by some of his remarks on the applicability of structure to induction and confirmation.

Ted writes:

Which observations confirm a generalization 'all Fs are Gs'? A natural answer is the "Nicod principle": observations of Fs that are Gs confirm 'All Fs are Gs'. But suppose that an observation confirms any logical equivalent of any sentence that it confirms. Then, as Hempel pointed out, the observation of red roses confirms 'All ravens are black' (given the Nicod principle it confirms 'All nonblack things are nonravens', which is logically equivalent to 'All ravens are black'.) And as Goodman pointed out, Nicod's principle implies that observations of green emeralds before 3000 AD confirm 'All emeralds are grue' (sice green emeralds observed before 3000 AD are grue.) But anyone who believed that all emeralds are grue would expect emeralds observed after 3000 AD to be blue.
[This conclusion] can be avoided by restricting Nicod's principle in some way -- most crudely, to predicates that carve at the joints. Since 'is nonblack', 'is a nonraven', and 'grue' fail to carve at the joints, the restricted principle does not apply to generalizations containing them. In Goodman's terminology, only terms that carve at the joints are "projectable". (35)

I'm confused about this strategy. Ted says we can avoid the conclusion that nonblack nonravens confirm ravens' blackness because 'nonblack' and 'nonraven' don't carve at the natural joints. But 'nonblack' carves at exactly the same joint as 'black' does -- to push the metaphor only slightly further, it's the very same cut. So if 'nonblack' isn't joint-carving, and is therefore nonprojectable, then it looks like just the same would go for 'black', and mutatis mutandis for ravens and nonravens. So now it looks like I can't confirm that all ravens are black by observing black ravens. This isn't the result Ted wanted, surely.

So I'm worried that one of these things must be true:

1. The story quoted above about why red roses don't confirm that all ravens are black is wrong;
2. Black ravens don't confirm that all ravens are black; or 
3. The 'black' joint is natural, but the 'nonblack' joint isn't.

When I asked Carrie about this, she suggested that Ted might be intending something like (3) here. After all, she pointed out, there might be more of an objective sense in which all black things resemble each other than that in which all non-black things do. I guess the thought would be that the metaphor is breaking down here; 'joint-carving' isn't the right term. Maybe this is right, but I didn't see that Ted could go this way, since he doesn't want to take objective similarity as the most fundamental thing. He wants structure to be most fundamental, and to explain objective similarity in terms of structure.

I feel like I must be missing something obvious here, but I can't see what it is. Somebody help?

Christoph Jäger on knowledge, contextualism and assertion

Christoph Jäger argues in a recent Analysis paper that contextualism and the knowledge norm of assertion are jointly untenable. Here’s my reconstruction of Jäger’s argument. (My numbering will differ from his.) Suppose that Keith has hands and the usual epistemic access to them. Also, Keith is a contextualist. For some two contexts, C-LOW and C-HIGH,

1. In C-LOW, “Keith knows that he has hands” is true.
2. In C-HIGH, “Keith knows that he has hands” is false.
3. In C-HIGH, Keith may appropriately state his contextualist theory.
4. In C-HIGH, “Keith knows his contextualist theory” is true.
5. In C-HIGH, “Keith knows that in C-LOW, ‘Keith knows that he has hands’ is true” is true.
6. In C-HIGH, “Keith knows that he has hands” is true.

But (6) contradicts (2), so something is wrong. Jäger says that it’s either contextualism or the knowledge norm that has to go. The first two premises are standard contextualist fare. A modest closure principle is invoked in the step from (5) to (6)—but it looks fine. The move from (3) to (4) follows from Jäger's version of the knowledge norm of assertion, which I do not contest. There are two action points here: the moves to lines (3) and (5). We consider them in turn.

Why should we accept (3)? Jäger introduces the set-up thus:

Consider a conversational context in which the contextualist states his theory. Such contexts are paradigmatic epistemology or 'philosophy classroom' contexts in which sceptical hypotheses are salient and taken seriously.

This appears to me to be mere assertion; why should classroom contexts be skeptical ones? I know that David Lewis said they were, but David Lewis said a lot of silly things in that paper. This just isn’t a commitment of contextualism per se. Contextualism is a linguistic thesis, made on the basis of, among other things, facts about linguistic use. If we were really taking skepticism seriously, we would not help ourselves to such facts. Some contexts in which epistemology of this sort is being performed—this one, for instance—are not very skeptical at all.

Actually, I think, there is a deeper problem for Jäger’s claim to (3). Contextualism is a controversial theory; lots of smart people think it’s wrong. It’s a theory that I accept, but I don’t think the acceptance here is a kind of outright belief, and I don’t think my statements of contextualism are appropriately regarded as assertions—as attempts to transmit knowledge. But the kind of “appropriate stating” at issue in (3) would have to be assertions in order for a knowledge norm of the latter to put any pressure on the move to (4). It’s far from obvious that anyone in ordinary contexts (let along skeptical ones) should go around asserting that contextualism is true. (And I say this as a contextualist! I think contextualism looks like the best theory. That doesn’t make it a thing to assert in ordinary contexts.)

So there are two pretty serious problems with premise (3). Now let’s set aside those problems for the purpose of further argument, and consider line (5). The inference from (4) to (5) is supposed to follow directly from the content of the contextualist theory. Jäger writes:

[Someone denying this step] would have to argue that the contextualist can legitimately deny [(5)], i.e. deny that he knows when he asserts his theory, in CHigh, that there are low-standards contexts in which (it is true to say that) he knows that he has hands. The claim that there are such quotidian contexts, however, is a cornerstone of classical, anti-sceptical forms of contextualism.

I don’t feel the motivation here at all. Contextualism the linguistic thesis does not entail that Keith or anyone knows that he has hands; it doesn’t even entail that Keith or anyone has hands. (Obviously.) It is consistent with the truth of contextualism that you and I are brains in vats. So even if we became convinced that we could have high-standards knowledge of contextualism—say, because we have introspective access to meaning, and that access is more resistant to skeptical scenarios than perceptual knowledge—we could still abandon Jäger’s ship at the step to line (5). Sure, Keith knows-HIGH that contextualism is true; that doesn’t mean he knows-HIGH that he knows-LOW that he has hands—even granting whatever intra-context closure principle you want. We’d get that he knows-HIGH that in C-LOW, he’d be invoking a relatively weak standard if he said “I know I have hands”. It doesn’t follow that he knows whether he’d meet it.

So there are lots of ways to resist this argument.

Acting on knowledge under uncertainty

Susan, who is entertaining later this evening, is about to walk to the local market to buy some olives for cocktails. She now faces that famous perennial question whether to take her umbrella. We stipulate:

• Susan does not know whether it will rain during her walk.
• Susan's rational credence that it will rain during her walk is 0.4.
• The nuisance of carrying the umbrella on her walk will cost Susan 10 utils.
• The nuisance of being rained upon without an umbrella is -30 utils. (It is no nuisance at all to be rained on if she has her umbrella.)

It's pretty reasonable to suppose that in this case, Susan ought to take the umbrella; we calculate the expected value pretty straightforwardly. The umbrella costs 10, and gives her a 0.4 chance of saving 30. (30 * 0.4) - 10 = +2. If Susan takes the umbrella in a way sensitive to the positive expected value of doing so, there's a pretty strong intuition to the effect that she's done everything right.

As you know, cases like this one are sometimes thought to be problematic for the knowledge norm of practical reasoning. Alex Jackson's careful paper does a nice job separating different knowledge-norm-like commitments, but he identifies this kind of case as at least a prima facie challenge to the following determination thesis:

What one knows determines what it is rational for one to do (possibly in concert with one’s desires).

I like this determination thesis. (In fact, I like something stronger -- I think we should be after something more like metaphysical grounding, not just determination.) So I need a story about the case of Susan. The Hawthorne & Stanley story is that Susan, if she is acting appropriately, is acting on knowledge about epistemic probabilities. She says to herself: there is a 0.4 chance that it will rain; this thing that she says to herself is what she treats as a reason. And it is something she knows.

I'm pretty uneasy about this line, although I've never been able to put my finger on exactly what I don't like about it. There is something odd, it seems to me, about probabilistic contents playing these kinds of roles. I know that's not an objection; I'm just recording my uneasiness. Here, anyway, is an objection: suppose she doesn't know the relevant probabilistic claim. Suppose that, for all she knows, the chance that it will rain is 0.3.

Remember, this is evidential probability we're talking about; the difference between the chance's being 0.3 and its being 0.4 can't be made by meteorological facts wholly outside Susan's ken. Still, it's not at all implausible that Susan might not know, with that level of precision, whether her evidence probabilifies rain to degree 0.3 or 0.4. Indeed, my own evidence right now, it seems to me, puts the chances of its raining on me as I walk to work tomorrow right around that ballpark; but I have no idea whether it is closer to 0.3 or to 0.4. I hope you agree this is not a very implausible possible situation.

Notice also that if the probability really is only 0.3, then, given the stipulations above, Susan's expected value for taking the umbrella is negative. ((30 * 0.3) - 10 = -1) So under the current stipulations, for all Susan knows, taking the umbrella might have negative expected value. She doesn't know that she should take it. She does, we may allow, know that there is some chance of rain, but this doesn't look like a good enough reason to perform this action.

You might think about trying to gild the bitter pill at this stage, suggesting that if she doesn't know whether it's better to take it, then she really does violate the action norm in taking it, although she does so in an excusable way. This seems to be Hawthorne & Stanley's line. But I don't think we should take it. For it's consistent with our case here that Sarah is exceptionally well-attuned to the evidence. That is, if the chance really were only 0.3, then she wouldn't take the umbrella. This is of course totally consistent with her failure of introspective discrimination.

I think Hawthorne & Stanley were right to look to knowledge with contents other than that it will rain, but wrong to focus in on probabilistic ones, in part for the reason just offered: there's no particular reason to expect them to be known. (And also in part because of that feeling I haven't managed yet to articulate, that these things aren't the right kinds of things to be invoking in one's reasoning.) While there's no reason, it seems to me, to think that Sarah must know the probabilistic content, there is, it seems to me, good reason to think she must have some other relevant knowledge around. If, for example, you think that E=K, then the evidential probability must be probability conditional on some knowledge. Let that knowledge be the reason for action. What is it that is the relevant evidence? I don't know, it depends on how the case is filled out. Maybe something a forecaster said? Maybe the look of the clouds? Whatever it is, I say we understand Susan as acting on the basis of that evidence.

Can you get a case like this involving no such evidence? Alex Jackson tries to give us one. But this blog post is getting long and I'm getting hungry, so maybe I'll leave discussion of that for another day. 

Where does apriority live?

Here are some things that can be violent:

• Neighborhoods
• People
• Actions

Violence inheres in these different kinds of things in different kinds of ways. A violent person is liable to punch you in the face if provoked; that the neighborhood will never punch you in the face doesn't count against its violence. Still, it's not like there's not a general category, violence, that applies in some sense to violent neighborhoods, violent people, and violent actions. These things are certainly connected somehow or other.

When you have this kind of set-up, you can sensibly ask which kind of entity is the best candidate for a more fundamental bearer of the property. To put it a bit colorfully: where does the violence live? Although I can imagine some people disagreeing, it seems to me pretty plausible that the violence of a neighborhood is explained by the violence of the people who populate it, rather than vice versa. Violence doesn't live in neighborhoods. And what makes a violent person? It seems to me that it has something to do with a propensity to perform violent actions. On this way of answering the question, violence ultimately lives in actions. But maybe not, maybe there's no real way to understand a violent action independently of the violent character traits that make a person violent. Maybe violence ultimately lives in people, or in character traits. I'd be curious to hear arguments about this interesting question. It's not my area.

But my area has some similarly interesting questions, too. Consider apriority. Here are some things that can be a priori:

• Knowledge
• Justification of beliefs
• Justification for beliefs

If you believe in apriority, it's worth spending a bit of time thinking about where the apriority lives.

Review of Philosophy Without Intuitions

I've been working for a while now on a review of Herman Cappelen's book Philosophy Without Intuitions. (Here are my several blog posts about it from this fall.) I've now completed a first draft of a review. I include it in full below the jump here. (I also have a pdf here, if you prefer to read it that way.) Comments, as always, are welcome.

Arguments for Cappelen's 'Centrality'

Philosophy Without Intuitions is an extended argument against Centrality, the thesis that philosophers rely on intuitions as evidence. Herman's official conclusion is that "on no sensible construal of 'intuition', 'rely on', 'philosophy', 'evidence', and 'philosopher' is it true that philosophers in general rely on intuitions as evidence when they do philosophy." The broad argumentative structure of the book is this: Herman says that defenders of Centrality don't offer arguments in its favor, but that "I take it two kinds of arguments are tacitly assumed". These two arguments he then goes on, in the two parts of his book, to consider in detail and refute.

The dialectical strategy, therefore, affords a defender of Centrality with two significant avenues of response, short of taking on Herman's arguments head-on:

• One could maintain that Centrality carries enough prima facie plausibility that it does not require argument; in the absence of compelling arguments against Centrality, it is reasonable to accept it.
• One could offer an argument for Centrality other than the two Herman considers.

With respect to (1), it may be helpful to consider an analogy. Contemporary archaeology widely assumes the existence of a mind-independent external world. Practically all archaeologists assume that the kind of idealism espoused by the late British Empiricists is false; they treat as perfectly coherent the idea, for example, that there might be a skull underground that no one will ever see or learn about. But although the assumption that there is a mind-independent external world is extremely widespread among archaeologists, one rarely sees arguments for this conclusion offered. And as philosophers well know, providing a cogent argument for this conclusion is not at all straightforward. But it's hard to take seriously the idea that this omission constitutes any serious error qua archaeologist -- we think that (a) our colleagues in the archaeology department are proceeding perfectly reasonably, and (b) their assumption is probably true, even if we're not sure how to provide an argument for it.

Can the defender of Centrality respond to Herman in a parallel fashion? To be sure, there are some differences here -- Centrality is a claim about how philosophy works, and the archaeologists' assumption is a claim about the broader world. But it's not clear why such a subject matter claim should make any important difference here. We have two claims: philosophers use intuitions as evidence, and there is an external world; both are widely assumed, and neither is given much argument. Indeed, there's a case to be made that both seem to share a deeper property as well: it is not at all clear how in principle one would go about investigating them empirically. So if one antecedently just considers it obvious that philosophers rely on intuitions as evidence, I am not at all sure that one will feel compelled by anything in the book to change one's mind.

With respect to (2), I think that some philosophers have been convinced that intuitions must be playing important evidential roles, not because it is obvious from watching how philosophers work, but because of epistemological concerns. The philosopher I have in mind takes her cue from the apparent epistemological difference between certain philosophical judgments -- say, the judgment that Mr. Truetemp doesn't have knowledge -- and paradigmatic empirical judgments -- say, the judgment that it was sunny in Vancouver today. There is a straightforward perceptual story to tell about my epistemic access in the latter case; it is one that affords a central role to certain of my perceptual experiences. But it doesn't look very much like my knowledge about Mr. Truetemp works in the same kind of way. There just aren't any sensory experiences that I've had that seem relevantly akin to the visual experiences that established my perceptual knowledge. It’s all very well to say that it needn’t be an intuition that’s doing the justifying here, but, unless one is offered an alternate story, one is bound to remain less than fully satisfied. Herman is quick to emphasise that there are arguments underwriting my judgment about Mr. Truetemp -- and he's right, and I think that's significant -- but arguments proceed on the basis of premises, and what story are we to tell about my epistemic access to the relevant premises? Insofar as it doesn't seem very plausible that perceptual experience can ultimately be establishing the premises from which I can conclude that Mr. Truetemp doesn't know, one might be tempted to think that it must be some other kind of experience, which plays a similar role to that of perceptual experience.

Call this line of thought the ‘What Else?’ Argument (WEA):

1. People sometimes come to justified philosophical beliefs via armchair methods.
2. In many of these cases, no sensory experience is playing justificatory roles.
3. All justified beliefs must be mediated by something like sensory experience.
4. Intuitions are the best candidates for such experiences in the cases in question. Therefore,
5. In some cases, people come to justified philosophical beliefs with intuitions playing justificatory roles.

I do not endorse the WEA -- I reject premise (3). (You can also be a philosophy-skeptic, denying (1), or a Quinean, denying (2).) But I do think it plausible that it or something like it does motivate the thesis that intuitions are playing important evidential roles in philosophy. This is an epistemological argument, not a methodological one; it does not proceed, as the ones Herman considers do, on the basis of empirical claims about how philosophers go about constructing arguments (except for the uncontroversial-in-this-context premise (1)). The WEA-endorsing proponent of Centrality, it seems to me, escapes Herman's critique unscathed.

Casullo on Negative and Positive Approaches to Apriority

Chapter 1 of Al Casullo's book, A Priori Justification, explores various theories of a priori justification. In the penultimate step of the chapter, he's argued that the motivations behind various theories ultimately converge on two views -- one 'negative', and one 'positive'. This is from p. 31 (with his labels changed for simplicity):

• (Neg) S's belief that p is justified a priori if and only if S's justification for the belief that p does not depend on experience.
• (Pos) S's belief that p is justified a priori if and only if S's belief that p is justified by some nonexperiential source.

Thus stated, the negative characterization (N), Al says, is ambiguous, because of different ways in which justification can depend on experience. So (N) is disambiguated into:

• (Neg-Weak) S's belief that p is justified a priori if and only if S's belief that p is nonexperientially justified.
• (Neg-Strong) S's belief that p is justified a priori if and only if S's belief that p is nonexperientially justified and cannot be defeated by experience.

Of the three remaining views -- Pos, Neg-Weak, and Neg-Strong, Al goes on to claim that there are really only two, because Pos and Neg-Weak are equivalent. The rationale here seems to be the idea that  every justified belief has its justification due to a source, and any given source is either experiential or nonexperiential. Take a justified belief, and consider the binary question of whether its justification's source is experiential; Neg-Weak says yes if it is; Pos says no if it isn't.

But I think this bit of reasoning is too quick. I'm suspicious of the move from nonexperiential justification to derivation from a nonexperiential source. To equate Pos with Neg-Weak is to legislate in advance that for any justified beliefs, there is a source of its justification. That is to say, it assumes prior to argument that there is no original justification -- justification that does not depend on a source. But that there is such original justification is, it seems to me, a coherent view that occupies a spot in logical space. (For what it's worth, I also think it's true; Ben and I defend it in The Rules of Thought.)

Sources generate things that weren't already there. The assumption that justification for a priori justified belief must derive from a source is, I think, part of the motivation for supposing there must be some kind of faculty of intuition to serve as source.

I'm not sure whether there are nonexperiential sources of justification. But I'm firmly committed to beliefs that are justified in a way that doesn't depend on experience. If these two attitudes are jointly coherent, then Casullo is wrong to equate Pos with Neg-Weak.