The Arguments for Realism and Anti-Realism

The chances that any particular theory, even if it fits the data really well, is vanishingly small because there are some gargantuan or maybe infinite number of choices. The anti-realist response has to do with what they call the under-determination of theories. They say no matter how good your theory has done to describe the tests you've put it through, there are a huge number of other ones that could be contenders as well.