If I’ve accomplished nothing else in this series (previous post here), I hope to have somewhat dispersed the intimidating air that surrounds both Putnam’s model-theoretic argument and the current discussion of Newman’s objection. This air has two sources, I think.
First, both arguments make heavy use of formal model theory. Formal logic, model theory, and especially metatheory are imposing bodies of technical knowledge. They are mathematical. Most philosophers are only minimally acquainted with them. Most graduate programs in philosophy today no longer require students to take metatheory, and even in the old days, the requirement was generally limited to a single course. I would imagine that over ninety-five percent of professional philosophers today could not tell you off the top of their heads what the Löwenheim–Skolem theorems even say. The point is that when people like Hilary Putnam and Michael Friedman start talking about Shoenfield absoluteness and ω-models, nearly all their listeners know they can’t talk to them as equals on that subject.
It’s now time for me to make a small confession, which is that I don’t care very much really about Hilary Putnam’s late-career misadventures with “internalism.” When I first went off to philosophy grad school many long years ago, Reason, Truth, and History was still relatively new and much talked about. I obtained a copy, but I could never get past chapter one. His arguments entailed certain claims that seemed to be just too obviously wrong. They still seem so to me now, and I have emphasized them in previous posts in this series. One is that a brain in a vat would not be able to think about whether it was a brain in a vat, even though the phenomenology of its thoughts would be identical to that of a normal, embodied person thinking (apparently) about being a brain in a vat. That entails that the brain in a vat has no idea what it is thinking about outside its own mind—and by the same token that neither do we. Another is that no natural relation, whether causation or anything else, can determine the referents of our thoughts and percepts, so that—assuming we reject “Platonism”—we have to admit that our thoughts and percepts do not have mind-independent referents. As I say, these claims seemed obviously false, even silly. Neither did it seem like the best use of time to delve deeply into Putnam’s reasoning and try to sort out what was wrong.
On the other hand, I do care about structural realism, which I have come to think is true but which has been bedeviled in recent decades by an argument essentially similar to Putnam’s model-theoretic argument. It has been to better understand and reply to the argument against structural realism that I have at long last performed the examination of Putnam’s model-theoretic argument presented in the previous posts in this series.
In the present post, I explain the argument against structural realism—which by now can be seen in fact to present no great difficulty—and comment briefly on the abysmal state of current discussion of structural realism. (The whole paper on which these posts are based is available here. To return to the third post in the series, click here. To skip to the fifth and final post, click here.)
In previous posts (such as this one and this one), I have sometimes alluded to the philosophy of structural realism. Structural realism says that we are unable to know the intrinsic character of the world outside our minds, although we are able to know a great deal about the structure of that world, especially its causally relevant features. Thus, we can know what we need to know to survive and thrive in our environment, we just can’t know what it is like intrinsically. For instance, we cannot know whether the surfaces of objects have the colors they appear to have in our visual perceptions of them or the hot and cold qualities we feel them to have, etc. Even the intrinsic character of spatial relations may not be as it appears to us. Still, the structure and dynamics of all these things is accessible to us—which is fortunate, because that is what matters for successful action.
I think structural realism is true and indeed inescapable. However, discussion of it in philosophy today is blighted by obsession with something called “Newman’s Objection,” after Max Newman, a Cambridge mathematician who published an important critique of Bertrand Russell’s version of structural realism as advanced in Russell’s book, The Analysis of Matter (1927). In my view, Newman rightly identified an important flaw in Russell’s structural realism, but not in structural realism per se, which has many options available for removing the difficulty. Unfortunately, many philosophers today, including many structural realists, treat Newman’s Objection against Russell (and subsequent formulations essentially like Russell’s), unless it can be refuted somehow, as a decisive refutation of structural realism itself. The result has been a lamentable lack of progress in developing the implications and insights of structural realism.
In what follows, I will explain how I think Newman’s Objection should best be handled and why it is a paper tiger. However, I have chosen to do so via an analysis of a much more well-known argument that in its essentials is practically identical with Newman’s, namely Hilary Putnam’s “model-theoretic argument” against the possibility that the terms of natural language or of our thoughts and percepts can have determinate referents in the mind-independent world.
This means that “what follows” is going to be a long haul! If anyone wants to read the whole paper in one fell swoop, it can be found here. Here at PoT, I will send it out in five installments, of which this post is the first. In this first installment, I begin with Putnam’s own warm-up exercise: his argument that a “brain in a vat” would be unable even to think that it was a brain in a vat. (To skip to the second installment, click here.)
In a trio of blog posts from 2010 (see here, here, and here), Sean Carroll defends the striking claim that, as far as concerns the basic physical principles that underlie the phenomena of everyday life, physics has been completed.
[T]here’s no question that the human goal of figuring out the basic rules by which the easily observable world works was one that was achieved once and for all in the twentieth century.
That’s right: “once and for all.” If asked for the basic, underlying story about why a table is solid or why the sun shines or what happens when a person flexes a muscle, modern science gives its answers in terms of “the particles of the Standard Model, interacting through electromagnetism, gravity, and the nuclear forces, according to the principles of quantum mechanics and general relativity.” One hundred years ago, explanations by this story (i.e., body of theory) could not be given, because this story did not exist. “But—here’s the important part—one thousand years from now, you will hear precisely that same story.”
I think Carroll is right, and I think the philosophy of structural realism can help to illuminate why. The purpose of what follows is to explain these points.
No, not those zombies! They aren’t merely possible, they are actual, as you can see. →
Rather, our topic today is philosophical zombies, beings that are physically identical to us but without conscious experience. Thus, a zombie version of yourself, for instance, would be atom-for-atom identical to you. It would share all of your behavioral dispositions: it would walk like you, talk like you, have the same tendencies to be angry, happy, or sad as you, report any information that you are able to report, and perform any tasks that you are able to perform. It would also remember everything that you can remember, know everything that you know, and it would have all the same politics and cultural attitudes and biases as you. At least, it would do all these things as near as we could tell. It would be behaviorally and neurophysiologically identical to you. There would be no way for another person to tell that your zombie twin was not you merely by comparing you with it, no matter what tests he might arrange. Nevertheless, your zombie twin would not be the same as you, because it would not have consciousness. That is, it would not have subjective experience. In the phrase widely adopted from Thomas Nagel’s well-known essay, “What Is It Like to Be a Bat?”, there would be nothing it is like to be your zombie twin.
Philosophical zombies are a way to make vivid an old philosophical argument, going back at least to Descartes, known as the Conceivability Argument. In the present version, the idea is that it is conceivable that the world could be just as it is physically down to the last elementary particle, but without conscious experience. That is, we could have had the Big Bang and the evolution of the universe just as it is, including the evolution of life on earth and the human species, and physically everything would be just as it is today, including all of us having discussions just like this one, although none of us nor any other beings have conscious experience. By conceivable, I mean there is no contradiction in this scenario and no reason that science can discover, whether physical, psychological, or otherwise, why it could not have happened. If this scenario is conceivable, then it seems we must conclude that consciousness is epiphenomenal: it is nonphysical, it cannot be explained by the physical, and its presence or absence makes no difference to the causal, functional, or physical order of nature.
A well-known argument, due to Frank Jackson, goes as follows. (You can read the short version here.) The brilliant genius Mary has complete knowledge of physical reality. All the sciences, physics, chemistry, neuroscience, etc., have been completed—there is nothing more to add—so that the fundamental physical constituents and causes of all phenomena are known, together with everything that supervenes on them, and Mary has mastered all of this. But although Mary thus knows everything about the physical world there is to know, she does not know everything there is to know. For, a peculiarity about Mary is that she has lived her entire life in a black and white room and has never been permitted to view anything except in black and white. Thus, on the day when she finally leaves her room and sees, say, a red object, she will learn something she didn’t know before. She will say, “Ha! So that is what seeing red is like.” If this is correct, then, apparently, red, or the experience of seeing red, is not part of physical reality.
The “Mary” argument is just one of several ways to bring out what is really an old, classic problem with any sort of reductionistic physicalism. It is this. Continue reading →
Policy of Truth 