Chapter 1
METAPHYSICAL AND SCIENTIFIC ACCOUNTS OF EMERGENCE: VARIETIES OF FUNDAMENTALITY AND THEORETICAL COMPLETENESS

John Symons

Department of Philosophy, The University of Kansas, Lawrence, KS, 66045, USA

SUMMARY

The concept of emergence figures prominently in contemporary science. It has roots in philosophical reflection on the nature of fundamentality and novelty that took place in the early decades of the twentieth century. Although it is no longer necessary to offer philosophical defenses of the science of emergent properties, attention to basic metaphysical questions remains important for engineering and scientific purposes. Most importantly, this chapter argues for precision with respect to what scientists and engineers take to count as fundamental for the sake of their uses of the concept of emergence.

INTRODUCTION

Two defining characteristics, novelty and naturalness, mark the concept of emergence. When emergent properties are first instantiated, they are said to be novel in some difficult to specify, but presumably nontrivial, sense. Although every moment of natural history is new in the sense of being at least at a different time from what came before, the kind of novelty that is associated with emergent properties is understood to constitute a metaphysically significant difference. What might that significance amount to? Very roughly, we can say that if an emergent property appears, there is a new kind of entity or property on the scene. Not just more of the same. To claim that a property, say for example a property like transparency, liquidity, or consciousness, is emergent is to make a judgment about the way it relates to more fundamental features of the world. The emergent property or entity differs in kind from that which preexisted it or is more fundamental than it. The first task of this chapter is to explore what it might mean for emergent properties to relate or fail to be related to more fundamental properties.

The discussion of emergent properties in scientific and philosophical research has emphasized discontinuities and differences between the emergent property and the prior or more fundamental properties from which it arises. However, emergent properties are not just discontinuous with what came before. They are also thought to be part of the natural order in some intelligible sense. According to most contemporary proponents, emergent properties are not unnaturally or supernaturally new (their appearance is not miraculous) but instead can be understood scientifically insofar as they are intelligibly connected with parts of the natural world and in particular with other properties that are prior or more fundamental.

The scientific problem of emergence involves understanding the relations between the emergent property and the more fundamental or prior properties. The practical payoff of this understanding is improved levels of prediction and control over those emergent properties and entities that concern us most.

TO EXPLAIN IS NOT TO ELIMINATE

How could there be an intelligible connection between metaphysically distinct kinds? In one sense, this is a question only a philosopher would bother asking. There are plenty of simple examples. Take Putnam's (1975, 295-298) famous example of the explanation for why a square peg fails to pass through a round hole. The rigidity of the pegs and the rigidity of the walls of the holes are dependent on their physical structure. However, the property of being able to pass through a hole of a particular size and shape is a different kind of property than the properties governing the physical constituents of the peg. Geometrical facts about the sizes of the cross section of the peg and the hole are sufficient to explain the facts about the pegs being able to pass through. An attempt to account for this higher level property in terms of the physics governing the particles in the peg would result in an unexplanatory, albeit a true and very long, description of the particular case. The geometrical explanation, by contrast is simple, provides clear guidance for interaction in the system and generalizes beyond this particular peg and hole to all pegs, all holes, and beyond.

The geometrical explanation explains many things at various scales, including why we have round manhole covers rather than square ones. Manhole covers have the property of not falling dangerously on people working in the sewers below because of the circular (rather than, say, rectangular) shape of the covers. This is one example of how we can intelligibly connect distinct kinds of properties. The microphysical properties of this particular peg, its particular material instantiation, can be connected with the macro-level property of passing through this particular hole via a geometrical explanation. That geometrical explanation has the virtue of being applicable beyond this particular case. The property of being a hole, being able to pass through, having a particular stable shape in space, having the particular microphysics that this peg has, and so on, are connected in the explanation in a way that satisfies our demand for explanation in this context perfectly.

Putnam intended this to be an example of a non-reductive explanation, as, he thought, the material constitution of the peg is almost completely irrelevant to the explanation of its fitting or failing to fit. His use of this example was meant to indicate the role of explanations that are not simply descriptions of physical microstates of systems. There is more going on in nature, he argued, than merely the microphysical.

Philosophers in the 1960s and 1970s were very concerned with the distinction between what they saw as reductive and non-reductive explanation. They fixated on the distinction between reductionist and anti-reductionist explanations because of their concern for the ontological implications of explanations. For some, the threat of reductionism is that we are encouraged to believe that one kind of object simply does not exist insofar as it can be described in terms of some more basic kind of object. This is an ontological concern. Notice that it involves a judgment that is independent of the process of explanation: We might decide that the existence of certain kinds of explanation license ontologies with fewer things in them. Thus, given the fact that we can explain traffic jams on the highway in terms of the interactions of individual vehicles, we might be tempted to draw the ontological conclusion that there is no traffic jam. Notice that if one decided to take this strategy with respect to one's ontology, it is a step beyond what the explanation of the traffic jam by itself tells us. In fact, I would argue, one needs to justify the step from a successful reductive scientific explanation to the claim that because of this successful explanation we can therefore eliminate the thing that has been explained from our ontology. Furthermore, in paradigmatically reductionist explanations, we see examples of intelligible relations being discovered between distinct kinds of properties. For example, subatomic particles are not the kinds of things that have properties like rigidity or wetness. A structural explanation of the subatomic constituents of a diamond goes some way toward explaining why the diamond in the engagement ring is rigid. There is an intelligible relation between the macro-properties of the diamond and the micro-properties of its constituents that adverts to the structure of the diamond crystal. Properties like hardness or rigidity are manifest only on some scales and result from interactions of large numbers of molecules. There is simply no non-relational explanation of why diamond molecules give rise to hardness. These relations, like the geometrical properties of Putnam's pegs, are not built into their relata.

The concern among philosophers is inspired by the concern that giving an explanation is equivalent to explaining away. Philosophers sometimes argue, following Carnap and Quine, that "explication is elimination" in natural science as well as in mathematics. This is due to a mistaken conflation of kinds of explanations and the diverse theoretical goals motivating explanatory projects. Quine's arguments concerning eliminativism were drawn from purely mathematical contexts. He was moved, primarily by his understanding of the history of analysis in nineteenth century mathematics. The infinitesimal is a puzzling artifact of early calculus that (according to popular opinion) we no longer need to include in lessons to high school students thanks to the work of Weierstrass, Dedekind, and Cantor. As the story goes, Weierstrass gave us the means to eliminate the infinitesimal, Dedekind and Cantor helped to finish the job. Quine strongly approved of this story and built his account of explication as elimination upon it.1 He proposed a view that began by individuating metaphysically puzzling notions in mathematics, like the infinitesimal or the ordered pair, via the mathematical roles that they play. Insofar, as they are "prima facie useful to theory and, at the same time, troublesome," Quine recommended that we simply find other ways to perform their theoretical role. Once we find these other ways, we can stop worrying about those concepts. Like the infinitesimal, they are eliminated (1960a, 266).

The explanatory project that motivates complexity science or other studies of emergent properties is not the same as that which motivated Quine's approach to philosophical analysis. For Quine, the method of philosophical analysis is to "fix on the particular functions of the unclear...