BRUSH REDUX
Brush is clearly denying a general predictionist thesis. By contrast he cites cases in which scientists themselves regarded known evidence explained by a theory as stronger support for that theory than new evidence that was successfully predicted.
And he seems to imply that this was reasonable. He offers an explanation for this claim, namely, that with explanations of the known phenomena, by contrast with successful predictions of the new ones, scientists had time to consider alternative theories that would generate these phenomena. Now, even if Brush does not do so, I want to extend this idea and consider a more general explanationist view that is committed to the following three theses that Brush invokes for some cases:1. A selection procedure for testing a hypothesis h is flawed, or at
least inferior to another, other things equal, if it fails to call for explicit consideration of competitors to h.
2. The longer time scientists have to consider whether there are
plausible competitors to h, the more likely they are to find some if they exist.
3. With putative evidence already known before the formulation of
h scientists have (had) more time to consider whether there are plausible competitors to h than is the case with novel predictions.
I would challenge at least the first and third theses. In my first example, selection procedure 1 for the drug hypothesis does not call for explicitly considering competitors to that hypothesis. Yet it does not seem flawed on that account, or inferior to one that does. However, even supposing it were inferior, whether a selection procedure calls for a consideration of competitors is completely irrelevant to whether the putative evidence claim is a prediction or a known fact being explained. In the case of a prediction, no less than that of an explanation, the selection procedure may call for a consideration of competitors.
For example, in our drug case, where h is “Drug D relieves symptoms S in approximately 95% of the cases,” and e is the prediction “In the next clinical trial of 1,000 patients suffering from symptoms S who take D, approximately 950 will get some relief” the selection procedure to be used for the next clinical trial might include the rule
In conducting this next trial, determine whether the patients are also taking some other drug which relieves S in approximately 95% of the cases and which blocks any effectiveness D might have.
Such a selection procedure calls for the explicit consideration of a competitor to explain e, namely, that it will be some other drug, not D, that will relieve symptoms S in the next trial. This is so even though e is a prediction. Moreover, to respond to the third thesis about time for considering competitors, an investigator planning a future trial can have as much time as she likes to develop a selection procedure calling for a consideration of a competing hypothesis. More generally, in designing a novel experiment to test some hypothesis h as much time may be spent in precluding competing hypotheses that will explain the test results as is spent in considering competing hypotheses for old data.
5.