Constructive empiricists believe that, even if a scientific theory makes numerous correct experimental predictions, we are not justified in believing that it tells us anything about reality–all scientific reasoning can reveal is that a theory makes correct predictions. Professor of Philosophy at King’s College David Kyle Johnson argues that this is mistaken. In response to Bas van Fraassen, who has written on this subject for the IAI, Johnson argues that, because scientific reasoning involves more than just experiment—historically, appealing also to qualities like parsimony and scope—it can reveal reality through inference to the best explanation.
In 2024, Princeton philosopher Bas van Fraassen wrote a short article for IAI News entitled “Science Does not Describe Reality: The Limits and Benefits of Explanation.” At the time, I was working on two projects (a science book and a Great Course) that, when completed, would (among other things) defend science’s ability to describe reality. I wanted to write a response to van Fraassen, but the projects demanded too much of my attention. But now that those projects are complete, I am in a position to explain the objections to van Fraassen’s thesis.
Summarizing van Fraassen’s argument
In a nutshell, his argument is this: What scientists do is make predictions based on theories and then invite others to test to see whether those predictions are borne out. “If theory T is right, result R should happen in experimental condition C.” Many think that running an experiment that shows that R happens in condition C is proof that theory T is true (and should be believed). But, van Fraassen argues, that R happened in condition C is only a reason to think that R happens in condition C. That’s the only observable, or empiricalresult we can actually see, so that is all that we are really justified in believing. (The underlying theory that made that prediction still may or may not be true.) That is why he calls those who accept his position “empiricists.”
Before I explain what is wrong with this position, let me explain what it gets right.
What van Fraassen Gets Right
First, a theory correctly predicting the results of an experiment is not, strictly speaking, “proof” that the theory is correct. The basic line of reasoning is this:
If the theory T is true, result R should happen. Result R did happen. Thus, theory T is true.
In other words:
“If T then R. R. Thus, T.”
This is a deductively invalid, fallacious mode of reasoning, called “affirming the consequent.” Those premises do not guarantee that the conclusion follows. “If I am in Pennsylvania, then I am in the USA. I am in the USA. Thus, I am in Pennsylvania.” Clearly that argument doesn’t guarantee its conclusion; neither does the above argument.
However, science is not a deductive method of reasoning; it is an inductive one. And inductive arguments merely try to raise the probability of their conclusion, not “prove” them for certain. Thus, the fact that an experimental result doesn’t prove a theory is true is irrelevant; it’s not supposed to. That is not what scientific reasoning is about.
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If the hypothesis that something exists clearly provides the best explanation for what we can observe, then the belief that it exists is what is rational.
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Source: iai.tv
