Justificationists often complain that Popper’s philosophy doesn’t enable us to pick out one scientific theory as being decisively the best at any particular time. But there is something extremely odd about this objection.
Critical rationalists advocate various restrictions on what theories we ought to prefer and those restrictions are quite hard to meet: a theory has to be experimentally testable, but not yet refuted, non-ad-hoc, explains how to solve problems and so on. So it isn’t the case that we say theories should be picked at random. We have tough standards. What criticism do justificationists have of those standards other than that they don’t justify anything? And that complaint is an empty one because there are unrefuted arguments indicating that justification is impossible.
Why should it be possible or even desirable to pick out just one theory? Different theories solve different problems and no single theory solves all of our problems. So why should we want to force ourselves to adopt just one of the inadequate theories floating around?
Let’s take an example. Quantum mechanics and general relativity can’t both be true, so we ought to eliminate one of them, right? But trying to say we shouldn’t use one of them when we don’t have a better replacement is only going to restrict our ability to solve problems, not increase it. And in any case, we can generate knowledge about the flaws in our theories and refrain from applying them to situations in which they’re useless. In other words, we can develop a preference about what we ought to do in any particular situation. Sometimes that preference will involving using quantum mechanics to do a calculation and sometimes we will want to use general relativity instead. So what problem is solved by coming up with a rule that prevents us from using quantum mechanics and general relativity in situations where we have no better option? I think quantum mechanics and general relativity will be replaced by better theories, but until then what would be the point in picking just one of them?
Also, sometimes scientists disagree with one another. Perhaps sometimes one side of a dispute is actually right and the other side is actually wrong. However, I can imagine that there are many occasions when the disagreement is just due to the different sides of the dispute paying attention to different problems. In other words, both sides are wrong and they have something to learn from one another. The idea that there should be some mechanical rule picking one side rather than the other as right and that this should be built into our epistemology seems unnecessarily restricting.
Moreover, scientific progress comes from generating lots of variations on our theories and then eliminating ones that don’t work. Eliminating variation by instituting a rule that picks just one theory would lead to stagnation.
UPDATE: A brief addition to make this post clearer. Any given theory is either true or false. We want to have true theories. We try to get true theories by solving problems: that is, by coming up with new theories that address problems with current theories. We do this by coming up with many different theories and discussing what problems they solve. Different people will have different ideas about what problems are important. This is appropriate in many cases because we learn what problems are interesting through conjecture and criticism. This means we can’t lay down hard and fast rules for what theory is the best at any particular time.
