Posted by ""John Gunkler"" <firstname.lastname@example.org>
Emergence is a tricky concept in the philosophy of science, albeit quite attractive intuitively.
Carl Hempl, in his ""Aspects of Scientific Explanation,"" wrestled with this concept. Here's what he said (in my words unless quoted):
1. The intuitive notion of ""emergence"" includes not merely being unexpected, but also being ""unexplainable, or unpredictable, on the basis of information concerning ... constituents of the system in which the phenomena occur ...."" And he provides the typical example of the characteristics of water (such as ""its transparence and liquidity at room temperature and atmospheric pressure, or its ability to quench thirst have been considered emergent on the ground that they could not possibly have been predicted from a knowledge of the properties of its chemical constituents, hydrogen and oxygen.""
2. This is appealing -- but, as you can see, requires quite a few assumptions about (a) what theories we have to predict physical characteristics of chemical compounds, (b) what ""constituents"" or ""parts"" are to be considered, and (c) what class of attributes of those constituents we are to infer from.
To illustrate point (c), it most definitely IS a characteristic of hydrogen that it, when combined suitably with oxygen, will form water (and we know the properties of water.) So, unless NOTHING could EVER be ""emergent,"" we need to find a way to rule out such characteristics of constituents, and Hempl suggests we do so by enumerating or otherwise defining a class of attributes for the constituents and then say that a certain characteristic of the ""whole"" be emergent with respect to this class of constituent attributes.
3. Hempl suggests a definition for emergence that doesn't have these obvious problems:
The occurrence of a characteristic, W, in an object, w [note: w is chosen to suggest ""whole""], is emergent relative to a theory, T, and part relation, Pt, and a class, G, of attributes if that occurrence cannot be deduced by means of T from a characterization of the Pt-parts of w with respect to all the attributes in G.
In this sense, then, I question whether there are any ""emergent"" events that arise from SD models. We can, and do, predict the behavior of systems from their constituent parts (structure.) What may, perhaps, be said is that SD provides explanations of events that are ""emergent"" with respect to other theories that have previously been invoked.
In fact, isn't that the main point of using system dynamics -- to explain what has previously not been well understood using previous theories and methodologies and constructs? We substitute our theory, our particular brand of mathematical modeling methodology, and the key construct of the feedback loop (and their interrelationships with other feedback loops) for the theories (etc.) of, say, economics or biology or ecology. Posted by ""John Gunkler"" <email@example.com> posting date Tue, 29 Nov 2005 11:18:09 -0600