But if all intentionality is derivative, then an infinite regress is in the offing. Pollack would defuse it in the Dennett manner, by arguing that it is finite:
Here is my response.
1. Original/Derived Intentionality. All will agree that there is some sort of distinction to be made here. A map is not about a chunk of terrain just in virtue of the map's physical and geometrical properties. Consider the contour lines on a topographical map. The closer together, the steeper the terrain. But that closer together should mean steeper is a meaning assigned by the community of map-makers and map-users. This meaning is not intrinsic to the map qua physical object. Closer together might have meant anything, e.g., that the likelihood of falling into an abandoned mine shaft is greater.
So some things derive their referential and semantic properties from other things. What about these other things? I draw you a map so that you can find my camp. I use the Greek phi to mark my camp and the Greek psi to mark the camp of a heavily-armed crazy man that you are well advised to avoid. I intend that phi designate my camp. That intending (narrow sense) is a case of intentionality (broad sense). This is not in dispute. What is in dispute is whether my intending is a case of original or of derived intentionality.
If the latter, then a regress ensues which appears to be both infinite and vicious. But before discussing this further, I need to bring in another point.
2. Ascriptivism Versus Realism. Dennett appears to hold an ascriptivist or projectivist or imputationalist or instrumentalist theory of intentionality: nothing is an intentional system intrinsically or an sich; a system is intentional in virtue of someone's assigning intentional states to it. Thus there is no fact of the matter as to whether or not my computer (when it is running a chess program) has beliefs and desires (e.g., the desire to inflict mate.) But it may be useful to take up the "intentional stance" vis-a-vis the computer in order to explain its behavior. Given the computer's complexity, the physical and design stances are unavailing.
A realist about intentionality, on the other hand, is someone who holds that some systems really are intrinsically intentional: their having beliefs and desires is not a matter of anyone's viewing them as having such states. One way to be a realist is by being a reductive realist. Such a person admits the reality of intentional states but identifies them with something believed to be more fundamental such as brain states. If you believe, with Dretske, that intentionality does not need naturalizing, but already is a natural phenomenon in the natural world below the level of conscious mind, then you are presumably a reductive realist about intentionality. You are saying this: there is intrinsic intentionality, but it is physical in nature.
I'm a realist too, but I hold that intentionality is irreducibly real: it cannot be reduced to, or identified with, anything else. It is what it is and not some other thing. Part of the reason I believe this is because the alternatives are quite hopeless.
3. The Ascriptivist Regress. Suppose one takes the ascriptivist line. Then an infinite regress appears unavoidable. Suppose I ascribe intentionality to my chess playing computer. Quite obviously, my ascribing, projecting, imputing, is itself an intentional state or a series of such states. So if ascriptivism is true, then my acts of ascribing must themselves be ascribed -- otherwise they are intrinsic and the game is over. This launches us on a regress that is obviously infinite since at each level, one can "kick it up a notch." It is also clear that the regress (unlike the truth regress say) is vicious since at no level is the explanation of intentionality complete.
One might think to avoid the regress by embracing a circle: I ascribe intentional states to the computer and it ascribes intentional states to me. But surely this is even more of an absurdity for reasons that needn't be belabored.
The upshot is that pure ascriptivism is incoherent.
4. Adulterated Ascriptivism. Perhaps the solution is to mix some realism in with the ascriptivism. Maybe it goes like this. I have a head full of homunculi. These little men and women, working together, ascribe intentionality to me. But each homunculus has its intentionality ascribed to it by other, stupider, homunculi which are constituents of it. The stupider homunculi, in turn, are composed of even stupider ones, and so on until we get to the level of individual neurons which, as Pollack says, "aren't 'about' anything." The base level homuncuili are so stupid that one could say that they don't even rise to the level of being either stupid or intelligent.
Does this avoid the dilemma of having to choose between a vicious infinite regress and a vicious circle? What Dennett is proposing is a finite regress that terminates with something naturalistically acceptable, namely entities that lack intrinsic or original intentionality.
Admittedly, this proposal gets rid of the infinity of the regress, but not its viciousness: we still have no explanation of intentionality. Consider the base-level homunculi. They are so primitive as to lack all intentionality. How then can they ascribe intentionality to their colleagues one level up? Surely it is obvious that the ascribing of intentionality is itself an intentional act or series thereof.
The point is quite simple. If the regress terminates with base entities utterly devoid of intentonality, then no higher level entities will be intentional. For the higher-ups get their intentionality only from the ones lower down in the hierarchy. If the ones at the very bottom have no intentionality, then they can't transmit it up. But if, on the other hand, the ones at the very bottom possess intentionality, then it is false that all intentionality is derived.
In the final analysis, Dennett is an eliminativist about intentionality. His position amounts in the end to the denial of intentionality. To see this, you just have to think clearly. Dennett is saying that all intentionality is derivative, none is intrinsic or original. But that makes sense only if one embraces an infinite regress. But in this case an infinite regress must be vicious. On the other hand, a regress that terminates either terminates with entities that are intrinsically intentional or entities that are not. If the former, the game is over. If the latter, no intentionality gets transmitted up and Dennett is an eliminativist.
5. Could Intentionality be Continuously Variable? Pollack thinks this is a reasonable assumption. Presumably he means that it is a matter of degree, not of kind. In one sense, this is unproblematic: I exhibit more intrinsic intentionality than my cat does in that my intentional contents are richer that hers are. I see the TV as a TV, whereas she sees it as merely something stable enough to support her weight should she decide to jump up on it. Similarly, one woman can be more pregnant than another if the first is farther along in her pregnancy than the second. But that is not to say that every woman is pregnant. So even if there is a sense in which some entities are more intentional than others, there still must be, on Dennett's scheme, entities that are devoid of intentionality. Otherwise, he must embrace panpsychism.
Now I am sure that Pollack is not a panpregnantist: he does not hold that all women are pregnant with mere differences of degree distinguishing them. I don't think he is a panpsychist either. If he isn't, then he holds that some entities are utterly devoid of mind. But then how are minded entities supposed to arise from them? Surely a mindless entity cannot ascribe intentionality to anything.
Note also that even if intentionality were variable, it is hard to see how it could be continuously variable. That would imply that there are continuum-many (2 raised to the power aleph-nought) gradations between my intentional contents and those of some other actual or possible being. It is not clear what that could mean.
A couple of remarks at first glance (I'm about to head home from work):
1) Quite right, I'm no panpsychist. I think intentionality, if it really exists, can be seen in the same way as the philosopher's "heap" - built from pieces that are not themselves heaps at all. In this way I think we can have a finite regress without eliminativism. I feel the same way about consciousness.
2) I wasn't arguing for a particular granularity of consciousness(/intentionality), either. There might be a finite number of possible levels between none at all and what we possess, or aleph-null, or even perhaps the continuum, c. While it is an interesting question, I don't see from here that it is fundamental to this discussion.
3) But yes, I do suspect that at root intentionality might be a concept with no bedrock ontological reality, an attractive cognitive and philosophical fiction. The intentional stance, on the other hand, is a very useful predictive tool.
I'm still curious about what you think about the intentionality of unconscious mental states!
Ad 1. You are of course under no obligation to defend the specifics of Dennett's theory, but given that he is an ascriptivist, I simply do not see how intentionality at any level above the base level can exist if it is not already present at the base level.
Ad 2. OK. I was perhaps overzealously seizing on your use of 'continuously' and taking it in its technical sense.
Ad 3. But now I wonder whether you really assimilated my point, namely, that to adopt the intentional stance, to regard a system as having beliefs, desires, and the rest, is to realize states that are themselves intentional.
As my friend Reppert would agree, what is exasperating about naturalists of the Dennett stripe is that they blithely presuppose the very thing they are supposed to be accounting for. They want to have it both ways: denying that intentionality
has any reality while making use of its reality.
My view is that nothing counts as mental unless it is at least potentially such as to be accompanied by consciousness. But more on this later.
I do imagine that levels of consciousness are for practical purposes continuous, but who knows? Most things in the world have turned out not to be; even time is now thought to be quantized. As I say, it might be an important question down the road, but not now.
What you are complaining about, if I understand you correctly, is that as you see it, to adopt the intentional stance regarding an object is itself to enter an intentional state - i.e. my mental state itself is now intrinsically about the given object.
But that really isn't a problem for us materialists: our brains enter a state that causes us to have predictable reactive dispositions to the object being considered. Those reactive dispositions are perceptible to us from within, too, and so our thoughts can be interpreted (either introspectively, or by an account of our state to a third party) as being "about" the given object. But this is as deep as the ontology of intentionality needs to go.
Also, regarding intentional ontology, you wrote "I do not examine my own states of consciousness to see what they are about." I have to disagree, and I will be glad to offer some examples, if you like. To give just one, imagine you are troubled by something, but you aren't sure what it is - just a vague worry - so you take a moment to review the things that have been on your mind lately and realize that what you are troubled by is the fact that your anniversary is approaching and you still have no gift for your wife. A nebulous worry (and by the way, cannot a generalized anxiety of this sort be a conscious mental state without an intentional object?) has revealed its intentional content only on a deliberate examination of the conscious state.
Consciousness most assuredly can examine its own contents, often with surprising results. Many have devoted their lives to this practice, in various forms, and with various goals.
Finally, you wrote:Imagine a mental state of the sort you describe. Presumably it has, by virtue of being a potentially conscious state, intentional content right now. But, as fate would have it, it turns out it never does become conscious. Is its intentional content then retrospectively destroyed? Perhaps we might call this Schrödinger's Thought. How are we to determine what mental states qualify for this distinction? It is far cleaner all around if we simply abandon this need for an objective ontology of intentionality.
I haven't seen Putnam's argument, and will look for it.
Given the difficulties that have attended the attempt to place original intentionality on a coherent ontological footing, we might be rescuing logic, not forsaking it, by letting go of the desire to do so, as Quine, Sellars, Dennett, the Churchlands, Davidson, Haugeland, Millikan, Rorty, Stalnaker, Hofstadter, Minsky, et al. have argued.
We can keep right on using folk language about beliefs to describe our complex reactive dispositions - such language is perfectly apt. There is nothing wrong with interpreting our own and others' behavior from the "intentional stance"; what seems to be unneccessary is the alleged underlying ontology.
Not exactly. I am not saying that to assume the intentional stance is to enter an intrinsically intentional state; I am saying that to assume the intentional stance is to enter an intentional state that is either intrinsic (original) or derived.
Then the argumentation proceeds as follows. If the state is intrinsic, then Dennett's ascriptivism is false since we now have a counterexample to the claim that a system's being intentional is a matter of ascription. But if the state is derived, then there must be a further system that ascribes the state in question. But the question arises again with this system: are its intentional states intrinsic or derived? If the latter, then an infinite regress ensues, a regress that is vicious.
Perhaps you might indicate whether you understand this reasoning. What you say in the next paragraph of your comment suggests that you have not understood it.
What you may be saying is something like this: When I impute intentional states to system S, my imputation is interpreted by me as being about S. No doubt. But the question is whether the imputation -- which is an intentional state -- is intrinsic or derived.
You appear to be dancing away from the problem.
One set of arguments is in Chapter 4 of Representation and Reality (1988).
The coherent ontological footing you are referring to, I believe, is scientific realism. Only those entities that appear in a scientific account of the world are allowed to be considered as real. Other entities are to be declared mythological or part of "folk" ways of speaking. No wonder it is difficult to put intentionality on such a footing. And qualia too.
Putnam describes the trajectory of Rorty, as of 1988, as an example of where he thinks eliminativism leads.
Putnam -
The problem facing the scientific realist in the philosophy of mind is simply this: if he gives up the idea that truth is a property, then he risks giving up his realism as well. This was, in fact, Rorty's trajectory; Rorty was at one time an eliminationist in the philosophy of mind, and has gone on to become an eliminationist with respect to truth and reference...as a result of which he has gone on to eliminate the whole problematic of scientific realism! On the other hand, if the scientific realist defends his realism in the traditional way ("correspondence theory of truth," etc.), then he is open to the charge that he has not eliminated the intentional at all; for reference is a paradigmatic intentional notion. To reject the propositional attitudes on the ground that they cannot be reduced to physical/computational properties while keeping the relation of "reference" (which is in exactly the same shape in this respect) is incoherent.
Two possibilities remain open. The scientific realist may abandon his eliminationism and try to develop an account of reference and/or the propositional attitudes in physical cum computational terms; this is the program of functionalism... [which most of the book is devoted to criticizing -HV] Or he may keep his eliminationism and try to meet the difficulties Field has raised. In this case he cannot simply argue that the propositional attitudes belong to folk psychology and must therefore be given up; this purely negative stance will not suffice. He has now taken on a positive program, the program of developing what Churchland called a "successor concept to the notion of truth" and of showing that we can account for our linguistic and scientific practice (including the use of classical logic) in terms of this successor concept. I would only say that until this program is more than a gleam in the eyes of some scientific realists, I do not myself expect it to succeed any better than the mentalist program or the functionalist program. To me it seems that what we shall have to give up is the demand that all notions that we take seriously be reducible to the vocabulary and the conceptual apparatus of the exact sciences. I believe it is reductionism that is in trouble - not intentionality itself. [end of quote]
A few years later, Putnam found a new term to characterize all the various reductionist programs: Utopian. It is clear that he intended this to mean something quite close to utopianism in politics; utopianism as a characteristic of 20th century thought.
Lonesome in here sometimes! I'm sure I'm not the only one left whose intuitions make him suspicious of the ontological underpinnings of original intentionality, but the others are certainly keeping mum.
Bill, when I wroteyou wrote in returnI confess that I did indeed simply assume that your view would be that my intentional state would in that case be intrinsic, conscious fellow that I am. But yes, I do understand the ascriptivist regress you refer to. But if we are to have "original" intentionality, then either it has to enter the picture somewhere in our evolutionary history as well, in what appears to be a magical moment of "ensoulment", or we have another regress. The difficulty with considering our intentionality any more intrinsic than that of our artifacts, and a naturalistic way of avoiding the problem of regress, is expressed by (who else?) Dennett (Intentionality, with Haugeland, 1988):And then, from his paper Evolution, Error, and Intentionality (1988)The point is to avoid regresses by building intentionality from simpler and simpler subsets - both in terms of evolutionary history, and in an analogous way in the modular architecture of the brain, as described elsewhere. This of course assumes that intentionality has a "heap"-like rather than a binary nature, but it seems to me that it is the right defense to the objections raised by Putnam as well. I suppose this would be the first of the "two possibilities" that "remain open" in the selection quoted by Henry.
As I have mentioned for several comments now, I am still very curious, if we are to insist on this sharp boundary between the mental (with its original intentionality) and the merely physical, to know where cases like the "Schrödinger's Thought" example I described above fit in. If intentionality depends merely on the potential for consciousness, but that potential is never actualized, it becomes difficult to see how the phenomenon at hand is distinguishable from a purely physical brain state that simply disposes the organism to certain reactions.
I imagine you will say that I still haven't answered your argument that there is an unbridgeable gap at the bottom of the intentionality chain. But this to me is like requiring that the grains of sand that compose a heap must themselves carry a sort of "quantum of heapness" as a sort of binary atomic property. I don't expect an individual neuron to do any ascribing whatsoever. This seems to me much more like panpsychism, which is not what I am sticking up for here.
By the way, sorry I haven't moved. I'm traveling to California tomorrow, and might have difficulty getting to the games for a few days. They are getting to the point where care must be taken.
It seems to me that whatever it is that is stored in memory is accessed by means of qualia or appears in awareness as qualia. If the qualia are not intentional, then the bridge between the non-intentional and the intentional is between qualia and the intentional states. So if, in the third person ontology, memory is a physical mechanism in the brain, it must be mediated by qualia, and the old problems with physicalism ensue.
(A side note: Your long list of philosophers might be investigated with respect to who is no longer on the list. At one time there was a whole herd of folks called behaviorists. Where have they all gone? One guy, Naom Chomsky, pretty much demolished that entire school of eliminationist philosophy. Not that I am a Chomsky fan.)
I realize that there has been some scattering of the ranks in the decades since the folks I listed declared their allegiances to this view, and looking back it was something of a cheap ploy just to list so many names. Still, these are legitimate thinkers all, and all have indeed been on this side of the fence. I'd like very much to check back in on these philosophers' more recent writing to see how their views have evolved (I do admit that much of what I have read by these people is by now quite a few years old). If you have links to any recent updates, in particular any recanting of the sort you describe, I would be interested.
That said, the naturalist ranks are by no means empty these days, and I have no doubt that lots of bright new faces have taken up the stations vacated by any apostates on the list.
It interests me very much that so many fine minds have attacked this issue without achieving a consensus. Why is that so?
Re memories and qualia, what about the forty-year-old memories my fingers have of how to play the the opening few bars of Mozart's Piano Sonata in A major? Or for that matter, there is the guitar solo from Stairway to Heaven, which I took the time to learn note for note at age 16 (I'm 49 now). Just the other day, for the amusement of my teenage son, I undertook to play it, and sure enough, there it was, still "wired in" in its entirety, although I had no idea whether I remembered it or not until I picked up the guitar and made the attempt. I have difficulty imagining what sort of quale those "qualify" as. They're just there, that's all.
I did not mean to say that your list is not still valid. I think it is. I was speaking rhetorically: the set defined as the collection of eliminationist philosophers at one time would have included the behaviorists.
I don't have a complete theory of memory. I was trying to take a stab at answering your question. There is undoubtedly a range of types of memory, including purely muscular memory. There also seems to be a range of qualia from the the very vivid to the very vague. A thought can be in the form of a voice, a sound-like quale, or more "abstract". What is the quale of an abstract thought? It doesn't resemble color, sound, taste, smell, etc, but it seems to have some sort of vaporous "feel".
Concepts have fuzzy boundaries (there is even a logic to help deal with this), but reality does not. A real thing is either really intentional or it is not. Even if you cannot tell whether a given state is intentional, that does not effect the fact that it either is or is not. I don't believe that your heap analogy helps at all in avoiding Bill's infinite regress.
I would respond to that by saying that intentionality is only a concept, too!
M
I also don't believe that derivitive intentionality is anything like the real thing. We use the word "about" in these two kinds of sentences:
1. The book is about science.
2. I was thinking about science.
but the word doesn't mean the same thing in the two sentences. There is at most an analogy between the two uses.
Well, just as you say you don't have a complete theory of memory, I do not in any way mean to suggest that I have a complete theory of intentionality, one of the more intractable questions in philosophy, and a matter that even first-tier professional philosophers (which certainly does not include me) cannot seem to resolve. What I do have is confidence in the notion that our mantal abilities are the result of our evolutionary history. At one time there was no intentionality in the world, and that now, apparently, there is, and I think there is a way to account for that without rejecting physicalism, even though that explanation may not yet be fully developed.
Dave, the post I mentioned (I'm working at it when I have time, but I have had no time this week), is not about intentionality per se, but about some related matters. I don't know if a great deal more to offer regarding intentionality. You wrote:.How do you know this? Might you be mistaken?
We have different prejudices - to you, and others in here, if physicalism conflicts with your intuitions about intentionality (such as that it is necessarily binary and noncomposite), then too bad for physicalism, whereas I say so much the worse for intentionality. To me our evolutionary provenance is much closer to being a bedrock fact of the world that the alleged atomicity of intentionality. So we are perhaps each playing Procrustes here, just a tad.
As of now, it sounds rather like the argument of an astrologist: "isn't is possible that there is some correlation between the movements of the planets and the lives of individuals on Earth?" Once you grant that possibility, a lot flows from it, so it is important to establish just how extremely improbable it is.
And to those of my ilk, the idea of immaterial mind-things that are taken to be on the same ontological footing as the tangible world seems like astrology too. Once you grant that possibility, a lot flows from it as well.
It might be too soon to say conclusively which of us is right, as awkward as that might be on a philosophy website.
That is what existence means for the tangible world, but that isn't what existence means for mind-things. Mind-things have a different ontology. To ask whether a mind-thing exists is to ask whether it has mental properties. A quale exists if it was experienced by some mind at some time (time is the only property I can think of that is shared by mental and physical objects).
You insist that to say of anything at all that it exists is to say that it has physical properties. What I do not understand is why you think physical properties are so special. What makes them so ultimate and universal? If you want to believe that only one kind of thing exists, then why physical? Isn't your evidence for the mental more direct and less subject to doubt? Why not say that only mental properties exist and that all physical properties must be reduced to the mental?
Your insistence on the majesty of the physical seems singularly unmotived. I take existence as I find it: mental, physical, ideal. Each kind of thing is separately apparent to me. But I am not doctrinaire. Give me an account of how one of these things might be reduced to the other and I will be amazed, thrilled, and greatly in your debt for an astonishing revelation. (The reason Whitehead so impressed me was that he came so close to reducing the physical to the mental. It was an astounding feat).
But until then, your dogmatic insistence that such a reduction is possible, in the face of such striking difficulties, seems to me to be blind faith. I, on the other hand am not relying on faith. I am an empiricist. I believe that mental objects exist because I have experienced them. I believe that abstractions exist because I have experienced them. And I believe that physical objects exist because I have experienced them. This is my experience. What have you to offer against that? Your hopes and dreams for a great unifying theory? Let me know when you find it. Until then, I'll just accept the obvious at face value.
X exists =df X is empirically detectable via the sense organs or their instrumental extensions (telescopes, microscopes, Geiger counter, etc). On this definition, EM fields would count as existent.
Is that what you are saying?
Dave: You make a good point when you say
See John Foster, The Case for Idealism (Routledge 1982).
But I think it might be better to describe yourself as a phenomenologist than as an empiricist since most empiricists have a narrower conception of experience than you do.
Fair enough. I do not deny that there I am guided to some extent by intuition in my adherence to physicalism, nor can I offer a conclusive and irrefutable defense of the position, any more than Democritus could when he posited that "nothing exists save atoms and the void".
Of, course, Dave, you must admit there are difficulties either way. You wrote:I would answer this by saying no, when you come right down to it all that you can be sure of is that you have had some traffic with mental objects. Any contact you may think you have had with physical things has only been in the form of the subjective qualia they appear to have presented to your awareness.
This way leads to idealism, of course, and if one keeps going after the road peters out, to solipsism.
I haven't read Foster's book, Bill, but idealism, I know, does have its own set of problems to solve, not least of which is that where we physicalist-leaning types have to account for the mental in terms of the physical, idealists have to account for the physical in terms of the mental.
There are a number of difficulties with dualistic answers to the nature of mind, and it is these objections, mostly, that push me in the direction I lean. I am expected to defend my "blind faith" in a physical origin of consciousness, but I haven't heard any explanations coming from the other side of the aisle of how these difficulties with dualism are to be resolved:
- It is plain that consciousness depends very sensitively on the physical state of the brain. Twiddling this or that neuron can induce memories, qualia, feelings, behavior, etc. Why is this the case, if our minds aren't simply something the brain is doing? Consciousness can be wiped out by tiny brain lesions, and personalities can be fundamentally altered by damage to the brain.
- How is the mind connected to the brain? How is the causal linkage of a nonmaterial entity to the macroscopic physical world achieved, without violating all sorts of conservation princicples?
- Where does the mind arrive from? At what point in embryonic development does the "ensoulment" take place? At what point in our evolutionary history? And if you have an answer for that, why then?
All of these problems seem more tractable from a physicalist point of view, and as I have said, I have heard no offers of any explanations at all from the dualist camp.
Again, one fo the things I find most striking about this debate is the fact that it has gone on so long, and with such brilliant thinkers on both sides, without either side converting the other to its view. Why is that, do you suppose? It's a serious question.
I draw confidence from the history of science itself. There have been so many examples of phenomena that, their mechanism not being known, have been declared to be beyond the reach of physical explication, only to yield up their secrets as our understanding of the physical world has deepened. It may be that the resolution of this, perhaps the ultimate conundrum, may result in some yet-unimagined synthesis of, or refutation of, both our viewpoints.
I respect your willingness to believe it when you see it, Dave.
I'm not sure how to answer your question, Bill. On the face of it your defintion feels about right, but it isn't subtle enough. I need to think about that one.
And even though I'm not really an idealist, I do think that idealism is much better supported than physicalism.
Better supported than physicalism? I don't know - idealism has some famous difficulties:
If things exist only in the mind, why do we agree on what they look like? I'm curious how one solves that problem without resorting to solipsism.
Do objects persist even when nobody is aware of them? Why? What accounts for my burying an object and its being found years later by someone else?
And so forth. Perhaps I was a bit glib about idealism in my previous comment (I do seem to be writing in too much haste lately), but idealism is a tough row to hoe.
(...any big rocks around here? I have the sudden urge to kick one.)
I'm curious also, how you have experienced abstractions other than as mental objects.
It's getting murky in here - we must be getting close to comment sunset.
Is the number four any less a shared thing than a tree? Do I have my own number four and you have yours? Then how do you know that my arithmetic applies to your numbers?
We share both trees and numbers, which implies that neither trees nor numbers are simply mental states. But why does the reality of the tree have to be any more substantial than the reality of the number?
To take an old example, we could both be brains in a vat, you and I, and still have shared world. But the public aspect of the shared tree in this case would be made, not of wood and leaves, but of electronic states.
The idealist who wants to escape solipsim needs to posit something shared between individuals, but that something need not resemble the physical world at all. In Berkeley's idealism, the shared something was just an idea in the mind of God.
God creates the tree as an idea, not a physical object. From God's idea of a tree flows a set of possible sense perceptions of the tree and those perceptions are presented by God when they are appropriate. But although there is actually something external to the perceiving minds --the idea in the mind of God-- the shared thing is nothing like our idea of a tree.
(I should note that although I believe this argument puts to rest objections due to shared objects, persistence, and the like, it is ultimately deadly to idealism. But the reasons are involved. Maybe I'll post it on my own blog when I get time.)
Not much time to respond here - I'm at work - but the naturalistic response to the abstracta-vs.-concreta question would be that we share the concept of "four" due to our common evolutionary heritage, which predisposes us to see the world in similar terms and categories, whereas we agree that there are trees because there are trees in the physical world (although the precise boundaries of the concept "tree" are not intrinsic, still there is a physical object there). I wonder whether all sentient lifeforms would necessarily have the concept of "four", and if so, why.In the spirit of Dr. Johnson, I doubt anybody has ever wrapped his car around a "three".
If we were brains in vats, we would still only have shared world by virtue of something common and external - presumably the computer running the software that was putting the same tree in your brain and mine.
As for ideas in the mind of God, we now come to an area where one can settle comfortably into the logically irrefutable, but only at the expense of relying on faith, something you seemed, above, to want to distance yourself from:
Those two examples show that it is possible for account for sharing and persistence without positing the existence of real physial objects. I don't have to actually ascribe to either view in order to use the view to show that your objection is answerable.
Well, as I said I don't think the brain-in-a-vat example really does it, because then we still need the vat. Really I think only either solipsism or faith in God manages the job.
I'm happy to acknowledge your not being an idealist, though I admit I am a bit unclear as to what exactly you do think is the correct model, though.
2. Disallowing comments from a particular person, or deleting an offensive, off-topic, or otherwise substandard comment, has nothing to do with censorship. People who think otherwise confuse censorship with lack of sponsorship. I am under an obligation not to interfere with anyone's exercise of legitimate free speech rights. But I am not under any obligation to aid and abet anyone's exercise of free speech rights, legitimate or illegitimate.
3. The Comments area is not an open forum for anyone to say anything about any topic. As the name implies, it is primarily for commenting on the author(s)' posts. But to comment on them, one must have read them. And if I have spent three hours on a post, a reader will not understand it in thirty seconds. Secondarily, the Comments area is to facilitate civil discussion between and among commenters as long as the discussion remains on-topic.
4. Some undesirables: The skimmers, those who cannot read but only read-in. The sophists who, abusing argument, argue for the sake of argument. The ideologues, those who are out for power, not truth. The uncivil. The illogical. The politically correct. Worst of all, perhaps, are those who exemplify the anti-Socratic property: those who think they know what they don't know. If Socrates was famous for his learned ignorance, these types are marked by their ignorant unlearnededness.