Last time, we discussed van Fraassen's criticism of Hacking's arguments for entity realism based on the Principle of Consistent Observation (as in the microscope case, most notably the grid argument). We also talked about Churchland's criticisms of van Fraassen's distinguishing empirical adequacy from the "pragmatic" or non-empirical virtues. Churchland argued that, based on what we know about perceptual learning, there's no principled reason to think that empirical adequacy is relevant to truth but simplicity is not.

Today we're going to look at an argument for scientific anti-realism that proceeds not by arguing a priori that observability has a special epistemological status, but by arguing that, based on what we know about the history of science, scientific realism is indefensible. Laudan discusses a form of realism he calls "convergent" realism, and seeks to refute it. Central to this position is the view that the increasing success of science makes it reasonable to believe (a) that theoretical terms that remain across changes in theories refer to real entities and (b) that scientific theories are increasing approximations to the truth. The convergent realist's argument is a dynamic one: it argues from the increasing success of science to the thesis that scientific theories are converging on the truth about the basic structure of the world. The position thus involves the concepts of reference, increasing approximations to the truth, and success, which we have to explicate first before discussing arguments for the position.

Sense vs. Reference. Philosophers generally distinguish the sense of a designating term from its reference. For example, "the current President of the U.S." and "the Governor of Arkansas in 1990" are different descriptive phrases with distinct senses (meanings), but they refer to the same object, namely Bill Clinton. Some descriptive phrases are meaningful, but have no referent, e.g., "the current King of France." We can refer to something by a description if the description uniquely designates some object by virtue of a certain class of descriptive qualities. For example, supposing that Moses was a real rather than a mythical figure, descriptions such as "the author of Genesis," "the leader of the Israelites out of Egypt" and "the author of Exodus" might serve to designate Moses (as would the name "Moses" itself). Suppose now that we accept these descriptions as designations of Moses but subsequently discover that Moses really didn't write the books of Genesis and Exodus. (Some biblical scholars believe the stories in these books were transmitted orally from many sources and weren't written down until long after Moses had died.) This would amount to discovering that descriptions such as "the author of Genesis" do not refer to Moses, but this wouldn't mean that Moses didn't exist, simply that we had a false belief about him. While we may pick out Moses using various descriptions, it doesn't mean that all the descriptions we associate with Moses have to be correct for us to do so.

Realists hold that unobservable entities are like that between changes in scientific theories. Though different theories of the electron have come and gone, all these theories refer to the same class of objects, i.e., electrons. Realists argue that terms in our best scientific theories (such as "electron") typically refer to the same classes of unobservable entities across scientific change, even though the set of descriptions (properties) that we associate with those classes of objects change as the theories develop.

Approximate Truth. The notion of approximate truth has never been clearly and generally defined, but the intuitive idea is clear enough. There are many qualities we attribute to a class of objects, and the set of qualities that we truly attribute to those objects increases over time. If that is so, then we say that we are moving "closer to the truth" about those objects. (Perhaps in mathematical cases we can make clearer sense of the notion of increasing closeness to the truth; i.e., if we say a physical process evolves according to a certain mathematical equation or "law," we can sometimes think of improvements of that law converging to the "true" law in a well-defined mathematical sense.)

The "Success" of Science. This notion means different things to different people, but is generally taken to refer to the increasing ability science gives us to manipulate the world, predict natural phenomena, and build more sophisticated technology.

Convergent realists often argue for their position by pointing to the increasing success of science. This requires that there be a reasonable inference from a scientific theory's "success" to its approximate truth (or to the thesis that its terms refer to actual entities). However, can we make such an inference? As Laudan presents the convergent realist's argument in "A Confutation of Convergent Realism," the realist is arguing that the best explanation of a scientific theory's success is that it is true (and its terms refer). Thus, the convergent realist uses "abductive" arguments of the following form.

If a scientific theory is approximately true, it will (normally) be successful.
[If a scientific theory is not approximately true, it will (normally) not be successful.]
Scientific theories are empirically successful.
Scientific theories are approximately true.

If the terms in a scientific theory refer to real objects, the theory will (normally) be successful.
[If the terms in a scientific theory do not refer to real objects, the theory will (normally) not be successful.]
Scientific theories are empirically successful.
The terms in scientific theories refer to real objects.

Laudan does not present the argument quite this way; in particular, he does not include the premises in brackets. These are needed to make the argument even prima facie plausible. (Note, however, that the premises in brackets are doing almost all the work. That's OK since, as Laudan points out, the convergent realist often defends the first premise in each argument by appealing to the truth of the second premise in that argument.)

Question: Could the convergent realist use weaker premises, e.g., that a scientific theory is more likely to be successful if it is true than if it is false (with a similar premise serving the role in the case of reference). Unfortunately, this would not give the convergent realist what he wants since he could only infer from this that success makes it more likely that the theory is true--which is not to say that success makes it likely that the theory is true. (This can be seen by examining the probabilistic argument below, where pr(T is successful) _ 1 and pr(T is true) _ 1, and PR(-) = pr(-|T is successful).)

(1) pr(T is successful | T is true) > pr(T is successful | T is false)
(2) pr(T is true | T is successful) > pr(T is true)
(3) PR(T is successful) = 1
PR(T is true) > pr(T is true)

That said, let's go with the stronger argument that uses the conditionals stated above. Without the premises in brackets, these arguments are based on inference to the best explanation of the success of science. As such, it would be suspect, for the reasons given before. Leaving that issue aside, Laudan argues that any premises needed for the argument to go through are false. Let us consider the case of reference first. Laudan argues that there is no logical connection between having terms that refer and success. Referring theories often are not successful for long periods of time (e.g., atomic theory, Proutian hydrogen theory of matter, and the Wegnerian theory of plates), and successful theories can be non-referring (e.g., phlogiston theory, caloric theory, and nineteenth century ether theories).

Next, we consider the premise that if a scientific theory is approximately true, it is (normally) successful. However, we wouldn't expect theories that are approximately true overall to result in more true than false consequences in the realm of what we have happened to observe. (That's because a false but approximately true scientific theory is likely to make many false predictions, which could for all we know "cluster" in the phenomena we've happened to observe.) In addition, since theories that don't refer can't be "approximately true," the examples given above to show that there are successful but non-referring theories also show that there can be successful theories that aren't approximately true (e.g., phlogiston theory, caloric theory, and nineteenth century ether theories).

Retention Arguments. Because the simple arguments given above are not plausible, convergent realists often try to specify more precisely which terms in successful scientific theories we can reasonably infer refer to real things in the world. The basic idea is that we can infer that those features of a theory that remain stable as the theory develops over time are the ones that "latch onto" some aspect of reality. In particular, we have the following two theses.

Thesis 1 (Approximate Truth). If a certain claim appears an initial member of a succession of increasingly successful scientific theories, and either that claim or a claim of which the original claim is a special case appears in subsequent members of that succession, it is reasonable to infer that the original claim was approximately true, and that the claims that replace it as the succession progresses are increasing approximations to the truth.

Thesis 2 (Reference). If a certain term putatively referring to certain type of entity occurs in a succession of increasingly successful scientific theories, and there is an increasingly large number of properties that are stably attributed to that type of entity as the succession progresses, then it is reasonable to infer that the term refers to something real that possesses those properties.

There are many ways a theory can retain claims (or terms) as it develops and becomes more successful. (We will allow those claims and terms that remain stable across radical change in theories, such as "paradigm shifts" of the sort described by Kuhn.) For example, the old theory could be a "limiting case" of the new, in the formal sense of being derivable from it (perhaps only with auxiliary empirical assumptions that according to the new theory are false); or, the new theory may reproduce those empirical consequences of the old theory that are known to be true (and maybe also explain why things would behave just as if the old there were true in the domain that was known at the time); finally, the new theory may preserve some explanatory features of the old theory. Convergent realists argue from retention of some structure across theoretical change that leads to greater success that whatever is retained must be either approximately true (in the case of theoretical claims such as Newton's Laws of Motion, which are "limiting cases" of laws that appear in the new, more successful theory) or must refer to something real (in the case of theoretical terms such as "electron," which have occurred in an increasingly successful succession of theories as described by Thesis 2).

Next time, we will examine an objection to retention arguments, as well as several replies that could be made on behalf of the convergent realist.