Commentary on Tom Radcliffe and Carolyn Ray's "A Conceptualist Interpretation of Quantum Mechanics"

David V. Ward

Radcliffe and Ray attempt to show the following in this paper:

1. Realism, in both the "scientific" sense, and as a theory of universals, is incompatible with quantum mechanics.

2. Conceptualism makes possible an interpretation of quantum mechanics which is preferable to those possible under either nominalist or realist theories.

The first point of note is that the authors wish to criticize realism in both its traditional senses. But quite different issues are at stake with respect to realist theories of universals and to realist theories of the objects of science. Platonism and its kin are, it seems to me, unworthy of defense. But scientific realism is another matter.

Radcliffe and Ray appropriately define scientific realism as the claim that, "...the world has a definite and mind-independent natural-kind structure...", a structure which we discover rather than project onto the world.

They take this to be in contrast to conceptualism, according to which the things named by universals are mind-dependent abstractions. They are "...mental entities based on similarities that the conscious subject notices between real objects." Further, th ese terms are "names for categories...based on similarities relevant to his purposes. His use of these categories...is as a result of his purposes as much as it is a result of the reality he's categorizing."

This is contrasted with what is presumed to be the realist view: "...it must be the case, to a realist, that we do not have any choice as to how to categorize reality: the categories are given by and in reality."

This latter claim is unfair to scientific realism, unjustly saddling the scientific realist with a Platonic natural kinds theory. Let me attempt one salient non-platonic natural kinds theory. There are lots of possible groupings of things, based on similar ities among them. All those similarity groupings exist mind-independently. But we make use of only a very few of them. We do not, to borrow an example from Hirsch, make use of the distinction between the portion of a car inside the garage and the portio n sticking outside, to form concepts of "incar" and "outcar". We could form concepts based on those distinctions, given that those distinctions in fact exist, but we don't. Why do we make use of some, but not other, similarity groupings as the basis of our conceptualizing?

Radcliffe and Ray make much of the purposes for which we categorize. But they treat this issue of purposes as much more context-dependent than it is. For, there is a purpose which motivates all our scientific theorizing, and indeed our conceptualizing in general. That purpose is explanation , which has a a future goal understanding. We make use of some similarity groupings (again, similarity groupings are based on real, mind-independent similarities among things ) and not others because some similarities are more important and effective in explanations of the world than others, and thus more conducive to understanding.

The realist need not claim that "we have no choice" about how we categorize reality, only that some categorizations are privileged because they play especially important roles in explanation. Those we characterize as "natural kinds". We have a choice, th e realist can claim, (for all groupings based on similarity actually exist) but we may not have a choice about what are the "best" similarity groupings to use. The "best" similarity groupings are those which produce the best, and most fundamental, explana tions.

I am using "explanation"here not in the psychological sense, but in the sense of a formal relationship between explanans and expanandum, as, for example, in the hypthetico-deductive model of explanation. (I am not endorsing this particular theory of explanation, but offering it only as an example of what I mean by explanation.) Presumably, explanations which embody the requisite formal r elationship between explanans and explanadum will be the most conducive to human understanding.

This discussion of explanation and natural kinds is important for an additional reason. Several of the important scientific figures discussed by Radcliffe and Ray, such as Bohr and Heisenberg, were heavily influenced by the "hot" philosophy of their time, logical positivism. In the view of the positivists, the fundamental purpose of science was prediction , not explanation . This view of science figures into the interpretations oof quantum mechanics to which Bohr and Heisenberg were inclined. If a theory is incapable of yielding predictions, then, from a positivist perspective, the theory is non-causal.

Bohr, Heisenberg, and other early quantum theorists and commentators seem to have simply uncritically accepted the positivist claim that if certain quantum values cannot be determined, that means there is no fact to the matter. That conclusion, however, is purely a matter of philosophical interpretation and is certainly not dictated by quantum theory. "Indeterminable" for the positivists simply meant "indeterminate", as a matter of (Kantian) phil osophical dogma. (A full and useful discussion of these matters can be found in James T. Cushing's Quantum Mechanics, Historical Contingency, and the Copenhagen Hegemony (Chicago: University of Chicago Press, 1994).

Radcliffe and Ray give a clear and convincing argument for the temporality of consciousness, but their argument for the spatial nature of consciousness is less convincing. Consciousness must be temporal, because consciousness consists of actions, and acti ons are temporal. But (considerations of special relativity aside), one can coherently conceive of consciousness non-spatially. That is, while Berkeleyan idealism is false, it is not incoherent.

In attempting to explain why humans cannot adequately conceive of quantum reality, Radcliffe and Ray propose laws of consciousness, one of which is: "What a thing is now and only what it is now causes what it does now". Continuing, they add, "The what a thing is" [of the above law] means 'how a thing is categorized by a consciousness'". If we substitute the meaning given for the phrase "what a thing is" into the original law, we get, "How a thing is categorized by consciousness now, and only how it is categorized by consciousness now, causes what it does now."

There are a number of points to be made about this puzzling formulation. The first is that it seems straightforwardly false. Suppose I habitually beat my dog with a particular stick, such that he becomes conditioned to react with fear-behaviors if the s tick is presented to him. If I now present him with the stick and he cowers, wouldn't it be a fair claim to assert that it is the history of the dog's encounters with the stick that now cause his behavior, that is is what the stick has been that accounts for its current causal efficacy? Again, our fundamental interest in science is explanation. We are interested in causes only because and insofar as they figure in explanations. This, in part, explains why we identify particular antecedent features as causes: we identify as causes those features which we have reason to believe yield better explanations.

The second, and more important objection is that it is odd to talk of "how we categorize" features of the world as "causing" what those features of the world "do". Perhaps we are to understand this claim in a straightforwardly Kantian sense, as suggested by the later claim in the paper that "...the law of causality pertains to our categorization of reality, not to mind-independent reality", and the paradigmatically Kantian claim by Radcliffe and Ray that "Likewise, the relationship between mind-independent reality and our categorizations is also non-causal, because mind-independent reality is non-local." Kant claims that we cannot say that the relationship between the noumenal world and the phenomenal world is causal, because causality is a category that a pplies only to the phenomenal world, and causality applies only to the phenomenal world because it is (one of) the categories (necessarily) schematized in terms of space and time, which are themselves creations of consciousness.

What I take to be the central argument by Radcliffe and Ray seems to be the claim that since consciousness is (necessarily) temporal and spatial, it cannot adequately comprehend (identify?, categorize?) nonlocal phenomena.

They say,

"When I say 'X is now Y' I am engaging in an act of identification, and declaring that I am now subsuming X under the category named by Y. My identifications must obey the law of non-contradiction and the law of causality. If I identify X as Y, I cannot also assert that X is simultaneously not-Y. And if I identify X as Y, I cannot also assert that it simultaneously acts as not-Y.

Identification by consciousness is, for the reasons given above, necessarily local identification."

First, when I declare that I am subsuming X under category Y, I can do so appropriately only if X is properly subsumed under Y . My choice to subsume X under Y is constrained by the facts about X and Y--namely, X must be of the sort named by Y.

Second, while the law of non-contradiction forbids me from claiming that X is both Y and not Y at the same time and in the same respect, it does not forbid me from claiming that X, which is now a Y, is now acting as not-Y. Bob, who is now an adult, is cu rrently acting as a child (a non-adult). An adequate defense of the claimed law, needed to defeat such counter-examples, would require much more detailed explication.

Third, it is not clear how it would follow from the quoted section that identification by consciousness is necessarily local identification. Realism, as with most other metaphysical theories, is flexible enough to allow for the possibility that most any empirical theory might turn out to be true. That is, metaphysical doctrines such as realism (or nominalism, or idealis m) are not subject to refutation by empirical results of the sort to which Radcliffe and Ray refer. Scientific theories are always subject to empirical refutation, and even unrefuted theories are subject to more or less constant revision and reinterpretat ion. Insistence on a particular interpretation of quantum mechanics can no more refute realism than Johnson could refute Berkeley by kicking a stone.

The experience of Newtonian physics provides a cautionary tale of the wisdom of tentativeness with respect to scientific theories. Classical physics had all the virtues: It integrated a wide variety of apparently disparate phenomena under a set of very s imple laws (so simple that we can teach them to high school students); it provided elegant and powerful explanations of physical phenomena; it withstood rigorous testing for an extended period, and it enabled us to create remarkable technological advances. Newtonian physics just looked like it must be true. Indeed, thinkers like Kant elevated Newtonian concepts to the status of necessary truths. Not only was space Euclidean, it must be Euclidean. It must be Euclidean as a matter of laws of thought , Kant held. We can think only in Euclidean terms.

But for all the plausibility and "naturalness" of Newtonian physics, for all the explanatory power and elegant simplicity, it is false. And physicists, if not the rest of us, now think in non-Euclidean terms routinely.

The tentativeness appropriate to our adherence to a particular scientific theory, and to a particular interpretation of that theory, is particularly relevant in this discussion. The standard interpretation of quantum mechanics is certainly not the only in terpretation consistent with the relevant data. Radcliffe and Ray devote only one sentence, for example, to Bohm's Quantum Potential theory. If Bohm's realist theory, or others, is consistent with experimental results, and if the formalism of the theory works, it seems simply rash to insist on the Copenhagen interpretation and to attempt to hang so much philosophical weight on the ultimate correctness of that interpretation.

That weight includes giving up a core notion of identity. Radcliffe and Ray say, in criticism, "Realism does not allow indeterminate identity..." Yes, and a good thing too! What would constitute "indeterminate identity"? The determinacy that the realis t insists upon amounts to the claim that things which exist do so in a particular way, and not others. The authors explicitly endorse the axiom that "existence is identity", which they say means that "Everything that exists, exists in a particular way." B ut Radcliffe and Ray claim that human consciousness, as a matter of a law of thought , is incapable of characterizing quantum phenomena in the "particular way" that quantum phenomena exist. They claim to have found, a la Kant, the limits of consciousness. This underestimates perhaps the ingenuity of physicists in creating new categorizat ions, new ways of understanding, and perhaps the power of consciousness to understand reality.

Part of my concerns center on the authors' insistence on one (disputed) interpretation of quantum mechanics. But the notion of conceptualism is also a concern. Conceptualism, they say, "...is a theory of universals which takes the things named by general terms to be mind-dependent abstractions. These mental entities are based on similarities that the conscious subject notices between real objects." Conceptualism thus holds that there are i n reality various similarities between objects. But it is just the existence of those real similarities that the realist needs to make his case. My concept of "dog" is based on real similarities among members of the canine class. But my concept is not identical with that class, or with the similarities which entitle each dog to membership in the class. I see no advantage, and some disadvantage, to designating concepts as universals rather than the similarity upon which the concept is based. A signific ant disadvantage is that conceptualism apparently has no way of handling our concepts of non-existent things. Our concepts, recall, are based on "...similarities that the conscious subject notices between real objects." What are we to say about our conce pts of such things as God, gnomes, fairies, unicorns, and the like? Since there are no such things, our concepts of them could not be based on observed similarities.

I have one final incidental criticism. In giving examples of what they call "substantial tautologies", Radcliffe and Ray give an account of Darwinian biology which is inaccurate in a respect relevant to their point in using it as an example. They claim, "'Survival of the fittest' entails a commitment to finding out how the concrete features of individuals contribute to their superior ability to reproduce. If features exist-and persist-that are demonstrably not conducive to an organism's reproduc tive success, then the doctrine of 'Survival of the fittest' would be called into question, and speculations about divine favor and special creation would gain some credence."

But Darwin's thesis is less subject to refutation than they claim--that is, "more tautological". Evolutionary biology does not claim that every persisting trait is conducive to an organism's reproductive success. It does not even claim that every persist ing trait is not harmful to reproductive success. All that can be said about any individual trait is that it has not proved so dysfunctional that it has killed off the organism or species, not that every persisting trait has survival value. Examples aboun d. The persistence of such features as human earlobes seems unlikely to be "conducive to the organism's reproductive success;" And there are certainly persisting traits which in fact hinder reproductive efficiency and success. Consider the anatomy of the human ovaries and fallopian tubes. In humans, the ovaries are not connected directly to the tubes, as they are in other species such as cattle. Human ova must be coaxed into the fallopian tubes after release by the ovaries, and some significant number e scape, with the result that pregnancy in humans is a much less certain business than with other species. Human reproductive success would, it seems, be enhanced if we possessed the "closed" ovarian-fallopian system of other species.